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VARIABLE APPROACHES INVESTIGATINGLIGHT QUALITY AND QUANTITYIMPACTS ON WARM- AND COOL-SEASONTURFGRASSESChristian BaldwinClemson University, [email protected]

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i

VARIABLE APPROACHES INVESTIGATING LIGHT QUALITY AND

QUANTITY IMPACTS ON WARM- AND COOL-SEASON

TURFGRASSES

A Dissertation

Presented to

the Graduate School of

Clemson University

In Partial Fulfillment

of the Requirements for the Degree

Doctor of Philosophy

Plant and Environmental Sciences

by

Christian Michael Baldwin

May 2008

Accepted by:

Dr. Haibo Liu, Committee Chair

Dr. Lambert B. McCarty

Dr. Hong Luo

Dr. Joe E. Toler

ii

ABSTRACT

Bermudagrass (Cynodon spp.) is the most popular warm-season turfgrass used in

warm climatic regions of the world due its recuperative ability, high traffic tolerance,

heat tolerance, and relative drought and salt tolerance. However, shade is a

microenvironment in which bermudagrass performs poorly. Morphological limitations,

such as reduced lateral stem growth and overall reduction of carbohydrate synthesis

contribute to bermudagrass, a C4 plant, decline under shade. Therefore, primary

objectives of this dissertation were to determine the genetic diversity of bermudagrasses

grown in full-sunlight and shade, impacts of shade and cultural practices on

bermudagrass spring transition, management recommendations to enhance bermudagrass

putting greens under shade, and the impact of different types of light on warm-season

turfgrasses. Secondary objectives of this dissertation determined winter shade and traffic

impacts on creeping bentgrass putting greens.

Due to the genetic variability and shade sensitivity of bermudagrasses, a two-year

replicated field and greenhouse study determined the morphological and physiological

characteristics and relative shade tolerance of 42 bermudagrass cultivars selected from

the 2002 National Turfgrass Evaluation Program (NTEP). In the field study, few trends

emerged where one cultivar could be recommended above all others. Also, experimental

cultivars performed well compared to industry standards throughout the year. For

example, „OKC 70-18‟ and „SWI-1046‟ (spring), „TiftNo.2‟ (summer), and „SWI-1003‟,

„SWI-1044‟, „SWI-1045‟, „SWI-1001‟, „TiftNo.4‟, „Tifway‟, and „TiftNo.2‟ (fall), were

in the top statistical category for turfgrass quality (TQ), shoot chlorophyll, clipping yield,

iii

root biomass, and thatch. In the greenhouse study, cultivars with best shade tolerance

were „Celebration‟, TiftNo.4, „TiftNo.1‟, and „Transcontinental‟. Cultivars with

intermediate shade tolerance included „Aussie Green‟, „MS-Choice‟, „Princess 77‟, „SWI-

1045‟, „SWI-1041‟, and „SWI-1012‟. Most shade sensitive cultivars included „SWI-

1014‟, „Arizona Common‟, „Sundevil‟, „SR 9554‟, „GN-1‟, and „Patriot‟. Greenhouse

results indicate genetic variability of shade tolerance exists among bermudagrasses, while

future bermudagrass improvement focusing on shade tolerance is promising.

Two lysimeter studies were conducted from March to July 2006 and 2007 to

evaluate fairway-type bermudagrass cultivars spring green-up (SGU) when shade is a

growth limiting factor and to evaluate the impacts of different cultural practices

(overseed, colorant use, and dormant turfgrass) and shade on „TifEagle‟ bermudagrass

(Cynodon dactylon (L.) Pers. X C. transvaalensis Burtt-Davy) spring transition and

summer performance. Fairway-type cultivars, Celebration and TiftNo.4, did not show

significant SGU delays due to shade in year II. However, Yukon and Riviera delayed

SGU 11% and 50% compared to full-sunlight treatments on 9 May 2007. Compared to

full-sunlight, TiftNo.4 and Celebration SGU and summer TQ was least affected by shade.

Although cultivar summer TQ differences were noted when grown under shade, all

cultivars TQ was below the acceptable threshold of 7 by 31 July. In another lysimeter

study, shade negatively impacted TifEagle bermudagrass SGU for all treatments on

various rating dates. By the end of May, overseed sun treatment had 39% greater SGU

compared to overseed shade treatment. Shade-grown colorant-treated TifEagle showed

~37% SGU reduction from week 2 through week 5 ratings compared to sun-grown

iv

colorant treatment. On the final SGU rating date, sun-grown colorant treatment enhanced

SGU 39% compared to sun-grown overseed treatment. This study indicates colorant-use

may provide an alternative to overseeding for bermudagrass by providing adequate

winter color at certain sites and a stronger bermudagrass base compared to overseeding.

A two-year field study from 15 June to 15 September 2006 and 2007 at Clemson

University determined the best combination of management practices for sustaining a

high quality „Champion‟ bermudagrass putting green under shade. Treatments included

55% full-day shade, trinexapac-ethyl (TE) applications (0.05 kg a.i. ha-1

2wk-1

), iron (Fe)

applications (2.7 kg a.i. ha-1

2wk-1

), and nitrogen (N) applications as urea (46-0-0) at rates

of 147, 293, and 437 kg ha-1

yr-1

. Overall, Fe applications had minimal impacts on

parameters measured. Increasing N rates linearly increased TQ when grown under full-

sunlight. However, increasing N rates linearly decreased TQ scores under 55% full-day

shade. Applying TE resulted in a linear TQ increase for full-sunlight and shade-grown

Champion bermudagrass. A 15% chlorophyll concentration increase was noted for TE-

treated plots compared to non TE-treated plots when grown under shade. Applying N at

293 kg ha-1

yr-1

increased thatch thickness 26% compared to the 147 kg ha-1

yr-1

N rate.

Champion bermudagrass did not provide an acceptable quality putting green when grown

under 55% full-day shade, however, adjusting chemical and cultural management

practices improved Champion bermudagrass putting green when grown under shade.

In 2007, two repeated greenhouse research projects were initiated to investigate

the physiological and morphological responses of „Diamond‟ zoysiagrass (Zoysia

matrella (L.) Merr), „Sea Isle 2000‟ (Paspalum vaginatum Sw.) seashore paspalum,

v

Tifway bermudagrass, and Celebration bermudagrass to various light spectral qualities.

Light treatments included a full-sunlight control and four different color shade cloths

filtering wavelengths 560 - 720 nm (blue shade cloth), 360 – 520 nm (yellow shade

cloth), 360 - 560 nm (red shade cloth) and 360-720nm (black shade cloth). Red to far red

ratio for each cloth was ~1.171, while percent light reduction for each cloth was ~65%.

Data collection included visual TQ, clipping yield, total shoot chlorophyll, leaf width,

total root biomass, root length density (RLD), specific root length (SRL), and root and

shoot total non-structural carbohydrates (TNC). Overall, black shade most negatively

inhibited parameters measured followed by blue shade, while yellow and red shade

performed similarly. For turfgrasses, Diamond was the most shade-tolerant, while

Tifway was the most shade-sensitive. Celebration and Sea Isle 2000 performed similarly.

This study implies different types of shade significantly impact the performance of warm-

season turfgrasses.

Two replicated field studies were conducted to evaluate winter shade tolerance

under various reduced light environments and winter traffic tolerance of „L93‟ creeping

bentgrass (Agrostis stolonifera var. palustris (Huds.)). In the first field study, objectives

were to evaluate winter shade tolerance of „L93‟ creeping bentgrass under various

reduced light environments (55% and 95%), including effects of morning vs. afternoon

shade, effect of trinexapac-ethyl (TE) (4-(cyclopropyl- -hydroxy-methylene)-3,5-dioxy-

cyclohexanecarboxylic acid ethyl ester) application on shade tolerance, and summer

month performance following a winter shade environment. Under shade stress,

consistent TE applications every two weeks during winter negatively impacted bentgrass

vi

growth and color, however, TE enhanced spring recovery from 95% winter shade

damage. Morning or afternoon shade minimally impacted parameters measured.

Overall, moderate to heavy winter shade may not limit creeping bentgrass performance as

a putting green in the transition zone. In a separate field study, treatments consisted of no

traffic (control), foot traffic, and walk behind mower traffic (rolling) at 0700 and 0900

when canopy temperatures were at or below 0oC. Under traffic stress, on all TQ rating

dates, 0700 rolling traffic decreased TQ by ~1.1 units compared to foot traffic at 0700.

In December, regardless of traffic application time, rolling traffic reduced bentgrass shoot

growth ~17%. By the end of March, all treatments had acceptable TQ. Root TNC and

shoot chlorophyll concentrations were unaffected in May and August. This study

indicates bentgrass damage due to winter traffic is limited to winter and early spring

months and full recovery should be expected by summer.

vii

ACKNOWLEDGMENTS

I would like to sincerely thank my major advisor, mentor, and good friend, Dr.

Haibo Liu. Thank you for your support and providing me an experience of a lifetime at

Clemson University. I look forward to future collaborations. Again, many thanks.

Also, I would like to thank my committee members for all of their unique

contributions. Many thanks for my good friend, Mr. Philip Brown, for the countless

hours assisting in many of my greenhouse projects. Thank you to Mr. Bud Sarvis, Mr.

Brandon Stiglbauer, Mr. Ray McCauley, and Mr. Steven Long for their friendship and

assistance in data collection and much needed assistance in maintaining our turfgrass

research plots. Also, thanks to Dr. Wes Totten for all of his help in measuring

carbohydrates.

Much needed thanks are in order for my parents, aunt, and grandmother. Without

all of your sacrifices and support, my success would not have been possible. All of you

have provided me with every opportunity to succeed in life. Thank you all again for your

encouragement and sacrifices made during my graduate school career.

Final thanks are in order for my wife, Victoria Baldwin. Your love and support

have allowed me to complete my graduate education. I look forward to our future

adventures together.

viii

TABLE OF CONTENTS

Page

TITLE PAGE ....................................................................................................................... i

ABSTRACT ........................................................................................................................ ii

ACKNOWLEDGMENTS ................................................................................................ vii

LIST OF TABLES ............................................................................................................ xii

LIST OF FIGURES ...........................................................................................................xx

LIST OF ILLUSTRATIONS .......................................................................................... xxii

CHAPTER

I. INTRODUCTION .............................................................................................1

II. LITERATURE REVIEW ..................................................................................5

Golf Course Landscape Related to Shade ....................................................5

C3 and C4 Photosynthesis .............................................................................6

Physiological Responses of Turfgrasses Grown Under

Shade .........................................................................................................8

Light Quality ..............................................................................................13

Anatomical Responses of Turfgrasses Grown Under

Shade .......................................................................................................16

Phytochrome and Gibberellins ...................................................................17

Plant Growth Regulators ............................................................................20

Cultural Practices .......................................................................................28

III. PHYSIOLOGICAL AND MORPHOLOGICAL

RESPONSES OF 42 BERMUDAGRASS

CULTIVARS .............................................................................................36

Introduction ................................................................................................36

Materials and Methods ...............................................................................37

ix

Table of Contents (Continued)

................................................................................................................ Page

Results and Discussion ..............................................................................41

Conclusion .................................................................................................56

IV. DIVERSITY OF 42 BERMUDAGRASS CULTIVARS

IN A REDUCED LIGHT ENVIRONMENT ...........................................60

Introduction ................................................................................................60


Results ........................................................................................................65

Discussion ..................................................................................................71

Conclusion .................................................................................................75

V. DORMANT BERMUDAGRASS SPRING GREEN-UP

INFLUENCED BY SHADE......................................................................76

Introduction ................................................................................................76


Results ........................................................................................................81

Discussion ..................................................................................................89

Conclusion .................................................................................................91

VI. WINTER CULTURAL PRACTICES AND SHADE

IMPACTS ON „TIFEAGLE‟ BERMUDAGRASS

SPRING GREEN-UP.................................................................................93

Introduction ................................................................................................93


Results ........................................................................................................98

Discussion ................................................................................................101

Conclusion ...............................................................................................104

VII. MANAGEMENT PRACTICES TO ENHANCE „CHAMPION‟

BERMUDAGRASS PUTTING GREEN UNDER

SHADE ....................................................................................................105

Introduction ..............................................................................................105

x


................................................................................................................ Page

Materials and Methods .............................................................................108

Results and Discussion ............................................................................112

Conclusion ...............................................................................................124

VIII. ALTERED LIGHT SPECTRAL QUALITIES IMPACTS

ON WARM-SEASON TURFGRASS GROWTH AND

DEVELOPMENT ....................................................................................126

Introduction ..............................................................................................126


Results ......................................................................................................135

Discussion ................................................................................................149

Conclusion ...............................................................................................154

IX. CREEPING BENTGRASS SEASONAL RESPONSES

TO VARIOUS WINTER LIGHT INTENSITIES ...................................155

Introduction ..............................................................................................155


Results ......................................................................................................162

Discussion ................................................................................................170

Conclusion ...............................................................................................175

X. VARIOUS WINTER TRAFFIC IMPACTS ON A

„L93‟ CREEPING BENTRASS PUTTING GREEN ..............................176

Introduction ..............................................................................................176


Results ......................................................................................................183

Discussion ................................................................................................188

Conclusion ...............................................................................................190

XI. SUMMARY AND PERSPECTIVES ............................................................191

APPENDICES .................................................................................................................198

A: Additional Tables and Figures .......................................................................199

xi


................................................................................................................ Page

B: Chlorophyll Extraction with DMSO ..............................................................203

C: Procedure for Nelson‟s Assay for TNC Analysis ..........................................204

D: Illustrations ....................................................................................................208

REFERENCES ................................................................................................................227

xii

LIST OF TABLES

Table ........... Page

1.1 Research history of turfgrass species responses when light

is a limiting growth factor ............................................................................3

2.1 Comparison of 31 turfgrasses shade adaptation

(Beard, 2005) .............................................................................................30

2.2 Classification of 42 bermudagrass cultivars relative shade

tolerance (adapted from Baldwin et al., 2008) ...........................................31

3.1 Spring green-up (SGU) of 42 bermudagrass cultivars rated

from 20 March to 21 April 2006 at Clemson University,

Clemson, SC ..............................................................................................42

3.2 Spring green-up (SGU) of 42 bermudagrass cultivars rated

from 20 March to 21 April 2007 at Clemson

University, Clemson, SC............................................................................44

3.3 Average weekly maximum/minimum air temperatures

(oC) and precipitation (cm) from 20 March to 27

April 2006 and 2007 in Clemson University, Clemson, SC ......................45

3.4 Turfgrass quality, clipping yield, shoot chlorophyll,

total root biomass, and thatch accumulation of 42

field-grown bermudagrass cultivars at Clemson

University in May, 2006 and 2007 ............................................................48

3.5 Turfgrass quality (TQ) of 42 bermudagrass cultivars

rated from June to August 2006 and 2007 at

Clemson University, Clemson, SC ............................................................50

3.6 Shoot chlorophyll, clipping yield, root biomass, and

thatch accumulation of 42 field-grown bermudagrass

cultivars at Clemson University in July, 2006 and 2007 ...........................52

xiii

List of Tables (continued)

Table ................................................................................................................ Page

3.7 Percent fall dormancy of 42 bermudagrass cultivars rated

from 1 November to 15 December 2006 and 2007 at

Clemson University, Clemson, SC ............................................................54

3.8 Turfgrass quality, clipping yield, shoot chlorophyll,

total root biomass, and thatch accumulation of 42

field-grown bermudagrass cultivars at Clemson

University in September, 2006 and 2007 ...................................................57

4.1 Turfgrass quality of 42 bermudagrass cultivars after

4 and 8 weeks of full-sunlight (control) and 64%

continuous shade at the Clemson University

greenhouse research complex ....................................................................66

4.2 Total shoot chlorophyll (mg g-1

) concentration of 42

bermudagrass cultivars after 4 and 8 weeks of

full-sunlight (control) and 64% continuous shade at

the Clemson University research greenhouse complex .............................68

4.3 Root length (cm) of 42 bermudagrass cultivars after

8 weeks of full-sunlight (control) and 64% continuous

shade at the Clemson University research greenhouse

complex ......................................................................................................70

4.4 Total root biomass (g) of 42 bermudagrass cultivars

after 8 weeks of full-sunlight (control) and 64%

continuous shade at the Clemson University research

greenhouse complex...................................................................................72

4.5 Overall shade tolerance rank of 42 bermudagrass

cultivars after 8 weeks of full-sunlight (control) and

64% continuous shade at the Clemson University

research greenhouse complex ....................................................................74

xiv


Table ................................................................................................................ Page

5.1 Spring green-up of six bermudagrass cultivars influenced

by various light regimes (full-sunlight and 55%

continuous shade) in spring, 2006 .............................................................83

5.2 Spring green-up of six bermudagrass cultivars influenced


continuous shade) in spring, 2007 .............................................................85

5.3 Turfgrass quality of six bermudagrass cultivars influenced


continuous shade) from 1 June to 31 July, 2006 and 2007 ........................87

5.4 Chlorophyll concentration (mg g-1

) and root total

non-structural carbohydrates (TNC) (mg g-1

) of

six bermudagrass cultivars influenced by various

light regimes (full-sunlight and 55% continuous shade)

in July, 2006 and 2007 ...............................................................................88

6.1 Spring green-up of 'TifEagle' bermudagrass influenced

by various winter cultural practices (colorant, overseed,

and dormant) and light intensities (full-sunlight and

55% continuous shade) recorded from 20 March to

15 May, 2006 and 2007 .............................................................................99

6.2 Turfgrass quality of 'TifEagle' bermudagrass influenced

by various winter cultural practices (colorant, overseed,

and dormant) and light intensities (full-sunlight and

55% continuous shade) from 1 June to 1 August,

2006 and 2007 ..........................................................................................100

6.3 Total shoot chlorophyll (mg g-1

) and root total non-structural

carbohydrates (TNC) (mg g-1

) of 'TifEagle' bermudagrass

influenced by various winter cultural practices

(colorant, overseed, and dormant) and light intensities

(full-sunlight and 55% continuous shade) in May and

July, 2006 and 2007 .................................................................................102

xv


Table ................................................................................................................ Page

7.1 Turfgrass quality of a „Champion‟ bermudagrass putting

green collected at day 1, weeks 4, 8, and 12 in response

to three nitrogen rates (147, 294, and 441 kg ha-1

yr-1

),

plant growth regulator regimes (trinexapac-ethyl at 0

and 0.02 kg ha-1

2 wk-1

), iron applications (0 and

2.7 kg Fe ha-1

2wk-1

), and two light environments

(full-sunlight and 55% full-day shade) at Clemson

University, Clemson, SC in 2006 and 2007 .............................................114

7.2 Clipping yield (g m-2

) of a „Champion‟ bermudagrass

putting green collected at weeks 6 and 12 in response

to three nitrogen rates (147, 294, and 441 kg ha-1

yr-1

),

plant growth regulator regimes (trinexapac-ethyl at 0

and 0.02 kg ha-1

2 wk-1


(full-sunlight and 55% full-day shade) at Clemson

University, Clemson, SC in 2006 and 2007 .............................................117

7.3 Total shoot chlorophyll concentration (mg g-1

) of a

„Champion‟ bermudagrass putting green collected

at weeks 6 and 12 in response to three nitrogen rates

(147, 294, and 441 kg ha-1

yr-1

), plant growth regulator

regimes (trinexapac-ethyl at 0 and 0.02 kg ha-1

2 wk-1

),

and two light environments (full-sunlight and 55%

full-day shade) at Clemson University, Clemson, SC

in 2006 and 2007 ......................................................................................119

7.4 Thatch accumulation, thatch thickness, and root total

non-structural carbohydrates of a „Champion‟

bermudagrass putting green collected at week 12

in response to three nitrogen rates (147, 294, and 441

kg ha-1

2 wk-1

), plant growth regulator regimes

(trinexapac-ethyl at 0 and 0.02 kg ha-1

2 wk-1

), and

two light environments (full-sunlight and 55% shade)

at Clemson University, Clemson, SC in 2006 and 2007..........................123

xvi


Table ................................................................................................................ Page


), lateral spread (g), shoot

width (mm), shoot chlorophyll (mg g-1

), root

mass (g m-2

), and root length density (mm cm3),

of 'Diamond' zoysiagrass, 'Sea Isle 2000' seashore

paspalum, 'Celebration' bermudagrass, and

'Tifway' bermudagrass under full-sunlight. .............................................136

8.2 Turfgrass quality of 'Diamond' zoysiagrass, 'Sea Isle 2000'

seashore paspalum, 'Celebration' bermudagrass, and

'Tifway' bermudagrass affected by full-sunlight and

various types of filtered light (~65% reduction) in a

greenhouse study ......................................................................................139

8.3 Relative clipping yield of 'Diamond' zoysiagrass, 'Sea Isle

2000' seashore paspalum, 'Celebration' bermudagrass,

and 'Tifway' bermudagrass affected by full-sunlight

and various types of filtered light (~65% reduction)

in a greenhouse study ...............................................................................140

8.4 Relative lateral spread of 'Diamond' zoysiagrass, 'Sea Isle



and various types of filtered light (~65% reduction)

in a greenhouse study ...............................................................................142

8.5 Relative shoot width of 'Diamond' zoysiagrass, 'Sea Isle



and various types of filtered light (~65% reduction) in

a greenhouse study ...................................................................................145

xvii


Table ................................................................................................................ Page

8.6 Relative shoot chlorophyll concentration of 'Diamond'

zoysiagrass, 'Sea Isle 2000' seashore paspalum,

'Celebration' bermudagrass, and 'Tifway' bermudagrass

affected by full-sunlight and various types of filtered

light (~65% reduction) in a greenhouse study .........................................146

8.7 Root and shoot total non-structural carbohydrates

(mg g-1

) of 'Diamond' zoysiagrass, 'Sea Isle 2000'

seashore paspalum, 'Celebration' bermudagrass, and

'Tifway' bermudagrass affected by full-sunlight and

various types of filtered light (~65% reduction) in

a greenhouse study ...................................................................................147

8.8 Total root biomass and root length density of „Diamond‟

zoysiagrass, „Sea Isle 2000‟ seashore paspalum,

„Celebration‟ bermudagrass, and „Tifway‟

bermudagrass affected by full-sunlight and

various types of light (~65% reduction) in a

greenhouse study ......................................................................................149

9.1 Winter surface and soil temperatures (oC) and percent

light reduction recorded at solar noon four times

weekly from 1 December to 28 February in

year I and II ..............................................................................................163

9.2 Turfgrass quality of 'L93' creeping bentgrass in

December, January, and February in response

to full-sunlight and 55% and 95% morning,

afternoon, and full-day winter shade (December

to February, 2004 to 2006) and trinexapac-ethyl

(0.02 kg ha-1

) applications every two weeks from

1 December to 31 July, 2004 to 2006 ......................................................164

xviii


Table ................................................................................................................ Page

9.3 Turfgrass quality of 'L93' creeping bentgrass in spring

and summer in response to full-sunlight and 55%

and 95% morning, afternoon, and full-day winter

shade (December to February, 2004 to 2006) and

trinexapac-ethyl (0.02 kg ha-1

) applications every

two weeks from 1 December to 31 July, 2004 to 2006 ...........................166

9.4 Chlorophyll concentration (mg g-1

) of 'L93' creeping

bentgrass in January, February, and May in

response to full-sunlight and 55% and 95%

morning, afternoon, and full-day winter shade

(December to February, 2004 to 2006) and


) applications every

two weeks from 1 December to 31 July, 2004 to 2006 ...........................167


) of 'L93' creeping bentgrass in

January, February, and May in response to

full-sunlight and 55% and 95% morning,

afternoon, and full-day winter shade (December

to February, 2004 to 2006) and trinexapac-ethyl

(0.02 kg ha-1

) applications every two weeks from

1 December to 31 July, 2005 to 2006 ......................................................169

9.6 Total root biomass (g m-2

) and root total nonstructural

carbohydrates (mg g-1

) of 'L93' creeping bentgrass

in January and February in response to full-sunlight

and 55% and 95% morning, afternoon, and full-day

winter shade and trinexapac-ethyl (0.02 kg ha-1

)

applications every two weeks from 1 December to

31 July, 2005 to 2006 ...............................................................................170

10.1 Turfgrass quality of „L93‟ creeping bentgrass without

(control) and with 24 foot and rolling winter traffic

applications at 0700 or 0900 recorded after each

24 traffic application dates from 1 December 2005

and 2006 to 1 March 2006 and 2007 .......................................................184

xix


Table ................................................................................................................ Page

10.2 Turfgrass quality of „L93‟ creeping bentgrass without

(control) and with 24 foot and rolling winter

traffic applications at 0700 or 0900 recorded weekly

and averaged per month from March to August,

2006 and 2007 ..........................................................................................185


) of „L93‟ creeping bentgrass without

(control) and with 24 foot and rolling winter traffic

applications at 0700 or 0900 in winter, spring, and

summer months in year I and II ...............................................................186

10.4 Chlorophyll (mg g-1

) concentration of „L93‟ creeping

bentgrass without (control) and with 24 foot and

rolling winter traffic applications at 0700 or 0900

recorded in winter, spring, and summer months in

year I and II ..............................................................................................187

10.5 Soil bulk density (g cm-3

) and infiltration rates (cm h-1)

collected end of February and root total non-structural

carbohydrates (TNC) (mg g-1) collected in May

following 24 treatment application dates with and

without (control) foot and rolling traffic at 0700

or 0900 from 1 December 2005 and 2006 to

1 March 2006 and 2007 ...........................................................................187

A.1 Bermudagrass (Cynodon dactylon (L.) Pers.) cultivars

selected for a field and greenhouse study to evaluate

morphological and physiological characteristics and

shade-tolerance at the Clemson University field

research plots and greenhouse research complex ....................................199

A.2 Average monthly surface and soil (7.6 cm depth)

temperatures (oC) of „L93‟ creeping bentgrass

during each 24 traffic treatment applications at

0700, 0900, and solar noon from 1 December, 2005

and 2006 to 1 March 2006 and 2007 .......................................................201

xx

LIST OF FIGURES

Figure Page

2.1 Simplified illustration of the C3 photosynthetic

pathway (A) compared to the C4 photosynthetic

pathway (B) (Miyao, 2003)..........................................................................9

2.2 Phytochrome structure consisting of a chromophore

and polypeptide region (Taiz and Zeiger, 2006). .......................................19

2.3 Biosynthesis of Gibberellic acid (Taiz and Zeiger, 2006). ...............................21

2.4 Chemical structure, common name, and a trade name

of trinexapac-ethyl .....................................................................................24

2.5 Type II PGR, trinexapac-ethyl, interrupting the enzyme

3β-hydroxylase from converting GA20 (a) to GA1 (b) in

plant gibberellin biosynthesis ....................................................................25

2.6 Chemical structure of flurprimidol ..................................................................26

2.7 Chemical structure paclobutrazol ....................................................................27

2.8 Type II PGRs, flurprimidol and paclobutrazol, inhibiting

the enzyme kaurene oxidase from converting

ent-kaurene (a) to ent-kaurenoic (b) acid in plant

gibberellin biosynthesis .............................................................................27

5.1 Monthly precipitation (cm) from 2 March to

31 May 2006 and 2007 and historical averages in

Clemson, SC ..............................................................................................82

5.2 Average monthly maximum and minimum temperatures (oC)

from 2 March to 31 May 2006 and 2007 and historical

averages in Clemson, SC ...........................................................................82

8.1 Portion of light spectrum filtered by the shading material

selected for a greenhouse experiment ......................................................130

xxi

List of Figures (continued)

Figure ................................................................................................................ Page

A.1 Daily and historical average maximum temperatures at

Clemson University, Clemson, SC in year I and II

from 1 December to 28 February 2005 – 2007 ........................................201

A.2 Daily and historical average minimum temperatures

at Clemson University, Clemson, SC in year I and

II from 1 December to 28 February 2005 – 2007 ....................................202

C.1 Standard curve used in Nelson‟s assay for determining

total non-structural carbohydrates content in

bermudagrass and bentgrass shoots and roots .........................................207

xxii

LIST OF ILLUSTRATIONS

Illustration Page

D.1 TiftNo.5 bermudagrass anatomical features including

bundle sheath (a), mesophyll cells (b), vascular

bundle (c), and epidermal cells (d). Image recorded

on 20 December 2005 at the Clemson University

Research Park, Clemson, SC, using a SEM-Hitachi

S3500N electron microscope ...................................................................208

D.2 Overview of 42 bermudagrass cultivars from the 2002

National Turfgrass Evaluation Program located

at the Clemson University field research plots ........................................209

D.3 Spring green-up comparison of „Riviera‟ (left) and

„Tifway‟ (right) bermudagrass selected from

the 2002 National Turfgrass Evaluation Program

at the Clemson University field research

plots. Image recorded: 18 April 2006 .....................................................210

D.4 Spring green-up comparison of „Midlawn‟ (left) and

„Celebration‟ (right) bermudagrass selected from

the 2002 National Turfgrass Evaluation Program

at the Clemson University field research

plots. Image recorded: 14 April 2007 .....................................................210

D.5 Percent dormancy comparison of „Aussie Green‟

(top-left), „Celebration‟ (top-right), and „TifSport‟

(bottom) bermudagrass selected from the 2002

National Turfgrass Evaluation Program at the

Clemson University field research plots. Image

recorded: 21 November 2006...................................................................211

D.6 Overview of a greenhouse study investigating the impact

of shade on 42 bermudagrass cultivars at the

Clemson University greenhouse complex ...............................................212

xxiii

List of Illustrations (continued)

Illustration ................................................................................................................ Page

D.7 „Tifway‟ (a), „TiftNo.4‟ (b), and „Celebration‟ (c)

bermudagrass response to 5 weeks of 64% continuous

shade at the Clemson University greenhouse

research complex .....................................................................................213

D.8 Root biomass of Celebration (left) and Tifway (right)

bermudagrass following 8 weeks of 55% continuous

shade at the Clemson University greenhouse complex............................214

D.9 Overview of a shade structure to investigate the

response of bermudagrass spring transition impacted

by 55% continuous shade located at the Clemson

University field research plots .................................................................215

D.10 Comparison of „Celebration‟ grown under full-sunlight

(a) and 55% continuous shade (b), TiftNo.4 grown

under full-sunlight (c) and 55% continuous shade

(d) and „Tifway‟ grown under full-sunlight (e)

and 55% continuous shade (f) adjacent to the

Clemson University field research plots ..................................................216

D.11 Spring performance comparison of „TifEagle‟

bermudagrass treated with a colorant (left)

and untreated (right) in the winter grown

under full-sunlight. Image recorded on May 1, 2007 .............................217

D.12 Spring performance comparison of „TifEagle‟

bermudagrass overseeded in the winter grown

in full-sunlight (left) and 55% continuous

shade (right). Image recorded on May 1, 2007 .......................................217

D.13 Overview of „Champion‟ bermudagrass shade study

at the Clemson University field research plots ........................................218

xxiv



D.14 „Champion‟ bermudagrass response to 147 (a), 294

(b), and 441 (c) kg a.i. ha-1

yr-1

of nitrogen (urea)

when grown under 55% continuous shade for 8

weeks at the Clemson University field research

plots ..........................................................................................................219

D.15 „Champion‟ bermudagrass response to 147 kg a.i.

ha-1

yr-1

of nitrogen (urea) with TE (0.02 kg

ha-1

2wk-1

) (a) and 293 kg a.i. ha-1

yr-1

of nitrogen

(urea) without TE (b) when grown under 55% shade

For 8 weeks at the Clemson University field research

plots ..........................................................................................................220

D.16 Overview of a greenhouse study investigating the

impacts of different light spectral qualities on

various warm-season turfgrasses at the Clemson

University greenhouse complex ...............................................................221

D.17 Root biomass comparison of „Sea Isle 2000‟ seashore

paspalum (top-left), „Celebration‟ bermudagrass

(top-right), „Tifway‟ bermudagrass (bottom-left)

and „Diamond‟ zoysiagrass (bottom-right) grown

under full-sunlight for eight weeks in the Clemson

University greenhouse complex. Image recorded:

13 June 2007 ............................................................................................222

D.18 Visual quality comparison of „Diamond‟ zoysiagrass

(top-left), „Sea Isle 2000‟ seashore paspalum

(top-right), „Celebration‟ bermudagrass (bottom-left),

„Tifway‟ bermudagrass (bottom-right) grown under

blue shade for six weeks in the Clemson University

greenhouse complex. Image recorded: 20 August 2007 .........................223

D.19 Overview of „L93‟ creeping bentgrass putting green

shade study initiated at the Clemson University

field research plots ...................................................................................224

xxv



D.20 „L93‟ creeping bentgrass response to rolling traffic

at 0700 (a) and rolling traffic at 0900 (b) at the


D.21 „L93‟ creeping bentgrass response to rolling traffic

at 0700 (a) and foot traffic at 0700 (b) at the


1

CHAPTER I

INTRODUCTION

Golf courses consist of two plant types (turfgrass and trees) expected to perform

optimally while competing for similar resources of water, sunlight, and nutrients. In this

unnatural ecosystem, turfgrass growth and development is often inhibited. Shade, a

major physiological stress, can rapidly alter morphological characteristics of a turfgrass

stand (Langham, 1941; McBee, 1969). Turfgrasses perform poorly in reduced light

environments due to high traffic volume, daily mowing, and reduced photosynthesis. In

shade, increased disease presence adversely affects cool-season turfgrass development,

while morphological limitations, such as reduced lateral stem growth, inhibits warm-

season turfgrass development (Beard, 1997).

Altered microenvironmental factors in shade negatively affect turfgrass

performance. Extended morning dew duration on turfgrass surfaces occur because tree

water transpiration is greatest at night (Dudeck and Peacock, 1992) encouraging disease

activity due to a more succulent growth (Beard, 1965). Dense shrubbery adjacent to

turfgrass areas impair wind movement reducing transpiration rates, increasing soil

moisture content, and decreasing carbon dioxide flux (Koh et al., 2003).

Cultural practices to enhance turfgrass performance in shade include raising

mowing heights (White, 2004; Bunnell et al., 2005b), reducing nitrogen (N) rates (Burton

et al., 1959), applying plant growth regulators (PGRs) (Qian et al., 1998; Qian and

Engelke, 1999a; Ervin et al., 2004; Bunnell et al., 2005b), and watering deeply and

infrequently (Dudeck and Peacock, 1992).

2

Numerous studies have noted the shade tolerance of many warm- and cool-season

turfgrasses (Table 1.1). Although bermudagrass, the most widely grown C4 turfgrass on

an international basis (Shearman, 2006), has been extensively studied, many challenges

and questions still remain when light is a limiting growth factor. Therefore, objectives of

this dissertation were to evaluate:

Diversity of bermudagrass cultivars grown in full-sunlight and reduced irradiance,

Shade impacts on fairway-type bermudagrass spring transition from winter

dormancy,

Impacts of various winter cultural practices and shade on putting-green

bermudagrass spring transition from winter dormancy,

Cultural management practices to minimize bermudagrass putting-green decline

under shade,

Bermudagrass responses to altered light spectral qualities,

Various winter light intensities and traffic impacts on creeping bentgrass.

3

Table 1.1. Research history of turfgrass species responses when light is a

limiting growth factor.

Bahiagrass

(Paspalum

notatum)

McBee and Holt, 1966

Bentgrass

(Agrostis spp.)

McElroy et al., 2006; Ervin et al., 2004; Tegg and Lane, 2004 a

and b; Koh et al., 2003; Steinke and Stier, 2003; Goss et al.,

2002; Bell and Danneberger, 1999 a and b; Chesnel et al., 1980;

Reid, 1933

Bermudagrass

(Cynodon spp.)

Baldwin et al., 2008; Bunnell et al., 2005 a,b, and c; Miller et al.,

2005; Stanford et al., 2005; Jiang et al., 2005; Jiang et al., 2004;

Tegg and Lane, 2004 a and b; Miller and Edenfield, 2002;

Coffey and Baltensperger, 1989; Gaussoin et al., 1988; McBee,

1969; McVey et al., 1969; McBee and Holt, 1966; Burton and

Jackson, 1964; Burton et al., 1959

Bluegrass

(Poa spp.)

Gardner and Wherley, 2005; Cereti et al., 2004; Tegg and Lane,

2004 a and b; Tan and Qian, 2003; Steinke and Stier, 2003;

Cockerham et al., 2002; Stier and Rogers, 2001; Stier et al.,1999;

Gilbert and Dipaola, 1985; Chesnel et al., 1980; Wilkinson and

Beard, 1975; Wilkinson et al., 1975; Wilkinson and Beard, 1974;

McVey et al., 1969

Buffalograss

(Buchloe

dactyloides

[Nutt.] Engelm)

Wu and Harivandi, 1995; Wu, 1990

Centipedegrass

(Eremochloa

ophiuroides

[Munro.] Hack.)

Barrios et al., 1986

Fescue

(Festuca spp.)

Gardner and Wherley, 2005; Wherley et al., 2005; Tegg and

Lane, 2004 a and b; Gilbert and Dipaola, 1985; Wu et al., 1985;

Chesnel et al., 1980; Wilkinson and Beard, 1975; Wilkinson et

al., 1975; Wilkinson and Beard, 1974; McVey et al., 1969

Perennial

ryegrass

(Lolium perenne

L.)

Cereti et al., 2004; Cockerham et al., 2002; Gilbert and Dipaola,

1985

4

Table 1.1. Research history of turfgrass species responses when light is a

limiting growth factor (continued).

Seashore

paspalum

(Paspalum

vaginatum

Swartz.)

Jiang et al., 2005; Jiang et al., 2004; Jiang et al., 2003

St.

Augustinegrass

(Stenotaphrum

secundatum

[Walt.] Kuntze

Trenholm and Nagata, 2005; Trenholm et al., 2004; Barrios et

al., 1986; Peacock and Dudeck, 1981; McBee and Holt, 1966

Zoysiagrass

(Zoysia spp.)

Bunnell et al., 2005c; Cockerham et al. 2002; Qian and Engelke,

1999 a and b; Qian et al., 1998; Reis et al., 2002; Barrios et al.,

1986; McBee and Holt, 1966

5

CHAPTER II

LITERATURE REVIEW

Golf Course Landscape Related to Shade

Beard (2005) defined shade as, “a turfed or ground surface overshadowed by

plant foliage such as a tree canopy or by an opaque structure; typically the interception of

sunlight occurs.” Trees are an essential component in the golf course landscape. For

example, Tom Lively, grounds manager at Medinah Country Club, estimated more than

12,000 trees are on the 640-acre property (Hollister, 2006). Also, Beard (1997) estimated

25% of turfgrass growth is limited due to various light restrictions. Trees provide shade

for players, make land use more efficient by separating two fairways, increase golf course

difficulty, enhance aesthetic value by screening roads, cars, and buildings, protect errant

shots from hitting pedestrians or cars, and provide a natural wildlife sanctuary and habitat

for birds (Beard, 2002). However, tree roots, which often extend outward two to three

times the tree height and can grow six feet in distance per year (Swayze, 2000), out-

compete the turfgrass root system for water and nutrients. Also, tree surface roots often

encroach bunkers, damage cart paths, affect playability, and damage equipment (Kind,

1997). Trees require additional labor and expense due to branches, twigs, pine cone, and

leaf removal prior to mowing (Lilly, 1999). Meanwhile, turfgrass maintenance

negatively affects tree health. Irrigation and equipment contacting tree trunks expedites

trunk decay, herbicides can damage tree foliage, and excessive vehicular traffic during

renovation periods damage tree roots (Lilly, 1999).

6

C3 and C4 Photosynthesis

Plants are unique organisms. Aside from certain photosynthetic bacteria, plants

capture and convert solar energy into chemical energy. Photosynthetic plant material

produce inorganic compounds needed for survival by fixing carbon dioxide (CO2) and

oxidizing water to produce oxygen and carbohydrates for sustained growth and

development.

6CO2 + 6H20 ----> 6O2 + C6H12O6

Two main carbon fixation mechanisms present in plants are the Calvin cycle and

Hatch and Slack pathway (Hatch and Slack, 1966).

Calvin Cycle

The Calvin cycle is unique to C3 plant species, however, it is present in all

photosynthetic plants and is responsible for the net conversion of CO2 to carbohydrates.

It primarily occurs in the chloroplasts (stroma) parenchyma cells with many enzymatic

steps including phosphorylation, de-phosphorylation, aldolases, and reduction

mechanisms.

Three key steps for continued function of the Calvin cycle include carboxylation,

reduction, and regeneration (Taiz and Zeiger, 2006). The first stable intermediate, 3-

phosphoglycerate (3-PGA), is formed when the receptor molecule, ribulose-1,5-

bisphosphate (RuBP), is carboxylated. The first stable intermediate is then reduced using

Carbohydrate Oxygen Water Carbon dioxide

7

light reaction products adenosine triphosphate (ATP) and nicotinamide adenine

dinucleotide phosphate (NADPH) to form a carbohydrate, glyceraldehyde-3-phosphate.

Glyceraldehyde-3-phosphate then produces sucrose or starch or regenerates the acceptor

molecule, RuBP, via adenosine diphosphate (ADP) (Taiz and Zeiger, 2006).

Hatch and Slack Cycle

The Hatch and Slack cycle is typical of C4 plant species. Unique characteristics

of C4 plants include low photorespiration rates, high photosynthetic rates, and minimal

water loss due to unique anatomical features compared to C3 plant species (Illustration

D.1). Two photosynthetic tissues in C4 photosynthesis are mesophyll and bundle sheath.

Carbon dioxide is primarily fixed in mesophyll cells, while Calvin cycle intermediates

are present in the bundle sheath. Many plasmodesmata exist between bundle sheath and

mesophyll tissues providing avenues of transport maintaining this highly coordinated and

complex pathway (Taiz and Zeiger, 2006).

There are four key stages in the C4 cycle (Taiz and Zeiger, 2006). Carbon dioxide

is fixed via phosphoenolpyruvate (PEP) carboxylase to produce oxaloacetate (OAA)

which is converted to a C4 acid, malate or aspartate, in mesophyll tissue. The C4 acids

are then shuttled to the bundle sheath via plasmodesmata where CO2 is released due to

decarboxlyation of the C4 acid. The released CO2 enters the Calvin cycle and is reduced

to carbohydrate products. Following decarboxlyation of either malate or aspartate, a C3

acid (pyruvate or alanine) is formed and shuttled back to the mesophyll where the CO2

acceptor, PEP, is regenerated (Taiz and Zeiger, 2006).

8

Plants with C4 anatomy maintain adequate CO2 concentrations near ribulose

bisphosphate carboxylase/oxygenase (Rubisco), which contributes to water conservation

on hot days and a positive net carbon gain when environmental CO2 is low (Figure 2.1).

However, this unique anatomical organization requires a higher energy demand to

maintain CO2 concentration gradients compared to the Calvin cycle (Taiz and Zeiger,

2006) and may reduce C4 plant species ability to adapt to variable environments, such as

low light. Also, C4 photosynthesis requires coordinated changes between mesophyll and

bundle sheath tissues, where C3 photosynthetic tissues require minimal coordination

(Sage and McKown, 2006). Specifically, C4 plants can not readily adapt to sunflecks

(typically occur in heavily shaded environments) due to distance between mesophyll CO2

fixation reactions and bundle sheath Calvin cycle metabolites (Horton and Neufeld,

1998). Also, light is a key component regulating several C4 cycle enzymes including

PEPCase, NADP-malate dehydrogenase, and pyruvate-phosphate (Taiz and Zeiger,

2006).

Physiological Responses of Turfgrasses Grown Under Shade

Shade reduces the photosynthetic efficiency of turfgrass leaves, leaving a

turfgrass stand vulnerable to daily mowing and traffic stresses. A reduction in leaf

sunlight capture results in carbon depletion followed by a decline in quality. Therefore,

net photosynthesis must exceed respiration for a healthy turfgrass stand (Wilkinson et al.,

1975). Reports on warm- and cool-season grasses have noted significant variations in

physiological characteristics responding to shade. Photosynthetic measurements can

9

Figure 2.1. Simplified illustration of the C3 photosynthetic pathway (A) compared to the

C4 photosynthetic pathway (B) (Miyao, 2003).

include dark respiration (plant energy use), net photosynthesis (balance of lost energy

plus energy being produced), light compensation points (least amount of light required to

sustain growth), total soluble proteins (major constituent of chloroplast stroma), and

carotenoid composition.

10

Warm-season turfgrasses

Physiological responses between „Sea Isle 1‟ seashore paspalum (Paspalum

vaginatum Swartz.) and „Tifsport‟ bermudagrass (Cynodon dactylon L. X C.

transvaalensis Burtt Davy) grown in a greenhouse for 32 days with ~80 mol m-2

s-1

were

investigated by Jiang et al. (2005). The authors indicated both cultivars had reductions in

parameters measured under low light compared to high light, but Tifsport had greater

reductions than Sea Isle 1. Tifsport grown in full-sunlight increased chlorophyll a 51%,

chlorophyll b 65%, carbohydrates 66%, total soluble proteins 55%, catalase 77%, and

ascorbate peroxidase 77% compared to shade grown Tifsport. Sea Isle 1 grown under

shade increased chlorophyll a 34%, chlorophyll b 36%, carbohydrates 52%, total soluble

proteins 22%, catalase 68%, and ascorbate peroxidase 41% compared to shade-grown

TifSport. The authors attributed greater Sea Isle 1 shade-tolerance to greater levels of

chlorophyll a and b, total soluble proteins, carbohyrates, and antioxidant enzyme

activities. In a similar study, Jiang et al. (2004) noted differences within seashore

paspalum cultivars and between seashore paspalum and bermudagrass cultivars. Under

70% and 90% continuous shade, all cultivars canopy photosynthetic rates (Pn) declined.

However, Sea Isle 1 (relatively shade-tolerant) had 48% and 63% greater Pn than

TifEagle bermudagrass (relatively shade-intolerant) under 70% and 90% shade,

respectively. Sea Isle 1 also had ~22% higher TQ score at 70% and 90% shade than

TifEagle. Regardless of shade tolerance, all cultivars grown in shade showed significant

decline for Pn rates compared to full-sunlight treatments. Compared to full-sunlight, Sea

Isle 1 minimized Pn loss (6% and 26%) while TifEagle Pn was reduced by 33% and 67%

11

compared to 70% and 90% shade, respectively. Results indicate relatively shade-tolerant

cultivars are more efficient in capturing and utilizing solar energy at low light intensities.

Miller et al. (2005) reported „Floradwarf‟ bermudagrass is more carbon-use

efficient than „Tifdwarf‟ bermudagrass when maintained at low light intensities. This

suggests Floradwarf is more adapted to longer sustained growth in low light

environments. In a separate study, Floradwarf (11%), Tifdwarf (20%), and „Reesegrass‟

(120%) bermudagrass had less efficient net photosynthesis compared to TifEagle and

„Champion‟ bermudagrass at 30% continuous shade (Miller and Edenfield, 2002). In

another study, St Augustinegrass (Stenotaphrum secundatum Walt. Kuntze.) increased

Pn, while „Tiflawn' bermudagrass decreased Pn at low light intensities (Winstead and

Ward, 1974).

Cool-season turfgrasses

Similar to warm-season turfgrasses, cool-season turfgrasses also demonstrate

photosynthetic variation in response to shade. Van Huylenbroeck and Van Bockstaele

(2001) noted more shade tolerant „slender-creeping‟ (Festuca rubra spp. trichophylla)

and „chewings‟ red fescue (F. r. L. spp. commutata), „crested hairgrass‟ (Koeleria

macrantha (Ledeb.) Schultes), and „rouhstalk grass‟ (Poa pratensis L.) reached light

saturation levels at a lower light intensity than shade sensitive perennial ryegrass (Lolium

perenne L.) and „strong-creeping‟ red fescue (F. r. spp. rubra). Wilkinson et al. (1975)

noted no significant Pn, light compensation point, or light saturation level differences

between „Merion‟ Kentucky bluegrass and „Pennlawn‟ red fescue. However, Pennlawn

12

had lower dark respiration rates than Merion at low light intensities. In conclusion,

Pennlawn was able to maintain a positive CO2 balance.

McElroy et al. (2006) subjected „Crenshaw‟ creeping bentgrass (Agrostis

stolonifera L.) in a greenhouse environment to high (47.9 mol m-2

d-1

) and low (4.7 mol

m-2

d-1

) irradiance treatments. Following a seven day acclimation period in a high or low

light environment, plants were transferred from high light to low light or transferred from

low light to high light. Carotenoid pigments, zeaxanthin, antheraxanthin, violaxanthin,

neoxanthin, lutein, lutein-5,6-epoxide (epoxylutein), and -carotene, were quantified.

Under low irradiance, lutein was the prominent carotenoid present (53%). Total

xanthophyll cycle was not as prevalent under high light conditions because of an increase

in zeaxanthin and antheraxanthin. Meanwhile, 24 hours after plants were transferred to a

low light environment, increases were noted for violaxanthin, lutein, and epoxylutein.

However, this increase was transient as a decrease was observed by hour 168.

Bell and Danneberger (1999b) noted violaxanthin may be an indicator of shade

stress for „Penncross‟ creeping bentgrass. Violaxanthin concentrations continuously

decreased from full-sunlight to temporal shade (morning or afternoon) to full-day shade.

Other carotenoids measured, neoxanthin and lutein, did not show this response to reduced

light stress.

Carotenoid composition of bermudagrass, based of previous cool-season turfgrass

reports, may be an interesting physiological determinant of shade tolerance. This type of

research has been limited to cool-season turfgrasses, in particular, creeping bentgrass.

Research of warm-season turfgrasses in this area is needed.

13

In general, relatively shade-tolerant turfgrass species and cultivars have a greater

ability of assimilating carbon at reduced light intensities as indicated by increased

photosynthetic rates in shade and the ability to reach light saturation levels at reduced

light intensities. Previous studies have shown photosynthetic capabilities have varied

within bermudagrass cultivars (Miller and Edenfield, 2002; Jiang et al., 2004 and 2005;

Miller et al., 2005). However, the warm-season turfgrasses selected in these studies have

been noted for their relative poor shade-tolerance (i.e. TifSport, TifEagle, Tiflawn,

Floradwarf, and Tifdwarf). It would be interesting to note the photosynthetic capability

of relatively shade-tolerant bermudagrass cultivars compared with industry standards

(i.e., Tifway and Tifsport) lacking shade tolerance. Previous studies have also focused on

light intensity rather than light quality. The significance of light quality altering turfgrass

photosynthesis deserves further investigations.

Light Quality

A turfgrass stand under shade can be inhibited by reduced photosynthesis (Jiang

et al., 2004; Miller et al., 2005), increased disease pressure (Beard, 1965; Vargas and

Beard, 1981) due to extended morning dew duration (Dudeck and Peacock, 1992),

reduced carbohydrate production (Bunnell et al., 2005 a and c), tree root competition

(Whitcomb, 1972; Whitcomb and Roberts, 1973), and reduced lateral stem growth

(Beard, 1997). Another factor affecting turfgrass growth and development under tree

shade are various qualities of filtered light. The photosynthetic active radiation (PAR)

available for plant growth is between 400 and 700 nm with ~90% absorbed by the plant

14

with the remainder reflected at the leaf surface or transmitted through the leaf (Taiz and

Zeiger, 2006). Blue light occurs from wavelengths 400 to 500 nm, green light 500 to 600

nm, red light 600 to 700 nm, and far-red light 700 to 800 nm (Taiz and Zeiger, 2006). In

nature, trees alter spectral quality available for turfgrass development, however, limited

research has investigated the light specific tree species filter in highly maintained

turfgrass environments. Also, most shade research has focused on light quantity by

filtering shade with black neutral cloths (Bell and Danneberger, 1999b; Koh et al., 2003;

Steinke and Stier, 2003; Bunnell et al., 2005b; Baldwin et al., 2008). The effect of light

quality on turfgrass performance is lacking and deserves research.

Gaskin (1965) demonstrated using a green shade cloth (75% light reduction) had

different light quality spectrums compared to white oak (Quercus alba L.) and maple

(Acer sp.) tree shade. McBee (1969) noted post oak (Quercus stellata) canopy filtered

wavelengths between 600 to 675 nm. Using a color temperature meter, which contains

two photocells deriving light quality indicating relative amount of blue and red light,

McKee (1963) indicated dense herbaceous shade such as lambsquarter (Chenopodium

album L.), ragweed (Ambrosia trifida L.), and smartweed (Polygonum pensylvanicum L.)

depleted blue wavelengths, while trees with a high canopy filtered red wavelengths. Bell

et al. (2000) noted conifer and deciduous tree shade (R:FR<1.0) altered spectral quality

available for turfgrass growth.

Previous investigations have noted plants vary in response to light quality.

McBee (1969) filtered wavelengths between 600-675 nm and wavelengths less than 575

nm with a 30% to 40% light quantity reduction. Bermudagrass cultivars selected

15

included Tifdwarf, Tifway, „Floraturf‟, and „Common‟. Blue light minimized stem

elongation while red light enhanced stem elongation. Shorter wavelengths (blue light)

were most important for a successful turfgrass stand, while minimal red light was

necessary for normal turfgrass appearance. McVey et al. (1969) also noted blue light

significantly enhanced quality and color while reducing clipping fresh weight production

and vertical shoot elongation in „Windsor‟ Kentucky bluegrass and „Tifgreen‟

bermudagrass.

Wherley et al. (2005) subjected „Plantation‟ (shade-tolerant) and „Equinox‟

(shade-sensitive) tall fescue (Festuca arundinacea Schreb.) to ~93% light reduction with

two different light quality regimes (R:FR >1 – neutral shade or R:FR < 1 – deciduous

shade). Trees selected were primarily Acer spp. and Fraxinus spp. Both cultivars grown

in deciduous shade produced significantly less tillering (~57%), greater leaf width

(~53%), higher chlorophyll levels (~40%), and greater leaf thickness (~24%) than neutral

shade (~93% light reduction) grown cultivars. High or low R:FR ratios did not impact

root growth.

Thorough anatomical, morphological, and physiological studies of bermudagrass

cultivars in response to various light spectrums are lacking. Light quality research on

bermudagrass is necessary to assist in management strategies of highly maintained

turfgrass areas. Results from light quality research benefits turfgrass managers by

providing information on various spectral qualities affecting bermudagrass performance.

A limited number of studies have demonstrated tree species alter light spectral

quality (McKee, 1963; McBee, 1969; Bell et al., 2000). Taking results from these

16

previous studies, continued research will specify the type of light certain tree species

filter. Future light quality research will further the understanding of how bermudagrass

cultivars respond when grown under specific tree filtered light. This information will

allow turfgrass managers to make informed decisions when trees or tree limbs are

considered for removal. Finally, light quality research is the first step in providing a

blueprint for golf course design by matching turfgrass cultivars that perform well under

specific light filtered by individual tree species.

Anatomical Responses of Turfgrasses Grown Under Shade

Turfgrass leaf anatomy alterations due to shade is poorly understood. Only a

handful of studies have been conducted since the 1970‟s. Also, the attention and focus

have been cool-season turfgrasses (Allard et al., 1991; Wilkinson and Beard, 1975;

Wherley e al., 2005). Due to genetic variation and breeding efforts of bermudagrass,

anatomical responses of shade-tolerant and shade-sensitive bermudagrass cultivars are

warranted.

Wherely et al. (2005) noted Plantation and Equinox tall fescue cultivars grown

under Acer spp. and Fraxinus spp. tree species providing ~93% light reduction produced

a significantly thicker epidermis compared to full-sunlight, while percentage of air space

in mesophyll tissues and grana thickness was unaffected due to different R:FR ratios.

Wilkinson and Beard (1975) noted the anatomical effects of Merion Kentucky

bluegrass and Pennlawn red fescue in response to low light intensities. Under shade,

Pennlawn had significant increases in vascular tissue, support tissue, and cuticle layer

17

than Merion. No differences in stomata density and chloroplast number and size were

reported between the two cultivars.

Allard et al. (1991) reported tall fescue leaves grown at low irradiance had 33%

longer epidermal cells and ~25% more epidermal cells per leaf blade than the high

irradiance grown fescue. Also, stomata density significantly decreased, while volume of

epidermis, vascular bundle, and mesophyll cells all decreased at 30% shade due to

reduced leaf thickness of shade grown plants.

Based on reduction of light quantity, these studies (Allard et al., 1991; Wherley et

al., 2005; Wilkinson and Beard, 1975) were in agreement that shade decreases stomata

density and length, reduces vascular and mesophyll cells, and increases percent air space

per unit leaf area. Bermudagrass leaf anatomy variation in response to shade (light

quantity and light quantity) has yet to be investigated.

Phytochrome and Gibberellins

Phytochrome

Phytochrome is a specific protein pigment that absorbs red (Pr) (650-680 nm) and

far red (Pfr) (710-740) light, as well as blue light, exhibits photoreversible properties, and

elicits many developmental responses in plants (Taiz and Zeiger, 2006). Phytochrome is

Pr Pfr

Red light

Far-red light

18

responsible for enabling plants to sense the length of night and allow plants to grow

toward or away from light sources. Phytochrome has also been linked to influence

flowering, leaf abscission, and dormancy. The structure of phytochrome consists of two

dimer subunits: a chromophore and an apoprotein (Figure 2.2). It has been proven that

Pfr gives rise to physiological responses within plants. Quality of light, rather than

quantity of light, mostly influences the interconversion of Pfr to Pr or Pr to Pfr. A non-

shaded microenvironment is typical of Pr/Pfr ratio greater than one, indicating red light is

not absorbed by an above tree canopy. A shaded microenvironment is indicative of a

Pr/Pfr ratio less than one, indicating a tree canopy filters red light allowing Pfr light to be

absorbed by turfgrasses. The significance of phytochrome in turfgrasses has received

little attention, however, due to the many shade environments present where turfgrasses

are grown, phytochrome activity logically plays a role in turfgrass species shade

adaptation.

Gibberellins

Gibberellins (GAs) were initially discovered in Japan by rice farmers who noted a

fungal disease caused their plants to grow tall and cease seed production (Taiz and

Zeiger, 2006). Currently, 136 naturally occurring GAs exist and function by increasing

stem, internode, and root elongation, promoting flowering and pollen development,

stimulating fruit-set, and possibly playing a role in seed development (Taiz and Zeiger,

2006). Altering GA status in turfgrass is of great commercial interest as turfgrass quality,

19

Figure 2.2. Phytochrome structure consisting of a chromophore and polypeptide region

(Taiz and Zeiger, 2006).

not biomass, is the main determinant of acceptable quality for turfgrass practitioners.

Gibberellic acid synthesis occurs via the terpenoid pathway in three distinct phases, each

occurring in different cellular compartments (Taiz and Zeiger, 2006) (Figure 2.3). PPhhaassee

oonnee occurs in plastids with ent-kaurene as the end product. The specific precursor to

GAs, geranylgeranyl disphosphate (GGPP), produces ent-kaurene via ent-copalyl

diphosphate. The sseeccoonndd pphhaassee occurs in the endoplasmic reticulum. An ent-kaurene

oxidase converts ent-kaurene to ent-kaurenoic acid which is then converted to GA12, the

http://4e.plantphys.net/image.php?id=197

20

first GA produced and the precursor for all other GAs in the plant. Also, this is the site of

type II PGR activity, such as paclobutrazol, impacting turfgrass growth and development.

PPhhaassee tthhrreeee often differs not only between species, but within the same plant in different

cellular compartments in the plant. Two pathways are known to exist, non-13-

hydoxylation or 13-hydroxylation pathway. The non-13-hydoxylation pathway converts

GA12 to GA9, which ultimately produces and oxidizes the bioactive GA4. Then, GA4 is

converted to an inactive form, GA34. The 13-hydroxylation pathway converts GA53 to

the inactive GA20 which is converted to the biologically active form GA1 via 3 -

hydroxylation. This is the enzyme which trinexapac-ethyl (TE) blocks. Three main

enzymes responsible for phase three of the GA pathway are GA 20-oxidase (encoded by

SLENDER gene), GA 3-oxidase (encoded by LE gene), and GA 2-oxidase (encoded by

SLENDER gene).

Plant Growth Regulators

Plant growth regulators (PGRs), Type I or II, have become a routine management

practice in turfgrass management. Turfgrass managers are continuously looking for

effective measures to suppress vegetative vertical growth, enhance plant resistance to

stresses, and improve disease resistance with the absence or reduction of environmentally

harmful products. In response to this demand, researchers have recently evaluated a

variety of PGRs effectiveness in:

Enhancing turfgrass quality, playability, and cultural practices:

21

Figure 2.3. Biosynthesis of Gibberellic acid (Taiz and Zeiger, 2006).

http://4e.plantphys.net/image.php?id=455

22

Increase ball roll (Yelverton, 1998; Fagerness et al., 2000; McCullough et

al., 2005 a and b)

Reduce mowing frequency (Weicko, 1997; Ervin and Koski, 1998; Goss

et al., 2002; McCarty et al., 2004; Pannacci et al., 2004; Tan and Qian,

2003; McCullough et al., 2006a and b; Totten et al., 2006; Ervin et al.,

2007; McCullough et al., 2007)

Decrease weed pressure (Isrigg et al., 1998; Gibson et al., 1998; Woosley

et al., 2003; Bigelow et al., 2007)

Enhance disease resistance (Golembiewski and Danneberger, 1998;

Avison et al., 2005; Stewart et al., 2008)

Reduce turfgrass encroachment (Johnson and Duncan, 2000)

Enhance turfgrass establishment (Isgrigg and Yelverton, 1999; Reicher

and Hardebeck, 2002; Kaminski et al., 2004; Zuk and Fry, 2005;)

Mitigating environmental stresses:

Drought (Jiang and Fry, 1998; Ervin and Koski, 2001a)

Heat (Heckman et al., 2001 a and b)

Sod tensile strength (Bingaman et al., 2001)

Salinity (Nabati et al., 1994; Baldwin et al., 2006; Shahba et al., 2008)

Freezing tolerance (Richardson, 2002; Steinke and Stier, 2004)

Shade (Qian et al., 1998; Qian and Engelke, 1999a; Stier and Rogers,

2001; Goss et al., 2002; Steinke and Stier, 2003; Tegg and Lane, 2004b;

Bunnell et al., 2005b)

23

Herbicide reduction in turfgrass species transition (Williams and Burrus, 2004;

Kraft et al., 2004)

Type I PGRs

Type I PGRs includes mefluidide (N-(2,4-dimethyl-5[[(trifluoromethyl)-

sulfonyl]amino]phenyl] acetamide) and maleic hydrazide (1,2-dihydropyridazine-3,6-

dione). Mefluidide prevents mitosis (cell division) and is often used to effectively inhibit

seed-head production, however, use in high quality turfgrass areas may cause turfgrass

discoloration (Watschke and DiPaola, 1995). Mefluidide is absorbed through foliage and

may inhibit GA biosynthesis (Watschke et al., 1992). These PGRs are applicable on golf

courses to reduce steep slope or ditch mowing (McCarty, 2005).

Type II PGRs

The most frequently used type II PGR, trinexapac-ethyl (TE) (Figure 2.4) [4-

(cyclopropyl- -hydroxy-methylene)-3,5-dioxy-cyclohexanecarboxylic acid ethyl ester],

is a structural mimic of 2-oxoglutaric acid which effects most steps of GA biosynthesis

following GA12-aldehyde (Rademacher, 2000). More specifically, TE effectively inhibits

GA20 to GA1 production (Adams et al., 1992) late in the mevalonic acid pathway

suppressing shoot vertical growth (Figure 2.5). Until the release of TE, PGR use on

highly maintained turfgrass areas was limited due to potential phytotoxicity (Shepard,

2002). Undesirable characteristics included phytotoxicity of treated leaves, reduced

recuperative ability, and increased weed pressure due to reduced competition from treated

turfgrasses (McCarty, 2005).

24

Researchers have established TE increases turfgrass leaf chlorophyll

concentration (Ervin and Koski, 2001b; Heckman et al., 2001c; Stier and Rogers, 2001;

Steinke and Stier, 2003; Bunnell et al., 2005b; McCullough et al., 2006a and b) because

TE reduces cell length and increases cell density (Ervin and Koski, 2001b). Total non-

structural carbohydrates (TNC) in cool- and warm-season turfgrasses have also been

enhanced using TE (Han et al., 1998; Waltz and Whitwell, 2005; Ervin and Zhang,

2007). Fagerness and Penner (1998) demonstrated the preferred site of absorption for TE

is the plant base, while roots absorb only 5% TE after 24 hours. Therefore, any inhibition

Trinexapac-ethyl (Primo Maxx, Syngenta Chem. Co., Greensboro, NC)

Figure 2.4. Chemical structure, common name, and a trade name of trinexapac-ethyl.

25

Figure 2.5. Type II PGR, trinexapac-ethyl, interrupting the enzyme 3β-hydroxylase from

converting GA20 (a) to GA1 (b) in plant gibberellin biosynthesis.

of root growth when applying TE is correlated to reduced shoot growth. However,

Beasley et al. (2005) reported „Moonlight‟ Kentucky bluegrass root length and root

surface area decreased ~47% by week 1 following a single TE application (0.27 kg a.i.

ha-1

), but increased from week 1 to week 4 compared to nontreated plants. Also, Beasley

et al. (2007) noted that TE reduced leaf canopy area. Repeated TE applications (0.11 kg

a.i. ha-1

) do not affect thatch development, rather increase shoot density and percent green

canopy tissue (Fagerness et al., 2001).

Trinexapac-ethyl appears environmentally safe. Haith and Rossi (2003) noted 6

applications of TE (80 g ha-1

) on creeping bentgrass maintained at greens height (3.5

mm) and fairway height (11 mm) was not hazardous to aquatic life in nearby water areas

due to low LC50 levels. Also, Fagerness and Bowman (2003) stated two TE applications

at 0.05 kg a.i. ac-1

in four week intervals did not increase nitrate leaching, rather increased

root and rhizome fertility recovery. Similarly, McCullough et al. (2006a and b) reported

A B

26

a TifEagle bermudagrass putting green treated tri-weekly with TE (0.05 kg ha-1

)

enhanced nutrient recovery in belowground tissue vs. above ground tissue.

Other type II PGRs, flurprimidol (Figure 2.6) (2R,3R+2S3S)-(4-chlorophenyl)-

4,4-dimethyl-2-(1,2,4-triazol-l-y1)pentan-3-ol) and paclobutrazol (Figure 2.7) ( -(1-

methylethyl)- -[4-trifluoromethoxy)phenyl]-5-pyrimidine-methanol), inhibit oxidation of

ent-kaurene to ent-kaurenoic acid catalyzed by monooxygenases (Figure 2.8)

(Rademacher, 2000) inhibiting GA production early in the mevalonic acid pathway

(Watschke and DiPaola, 1995). These growth regulators structures are unique in that an

electron pair is located on the hybridized N heterocycle which displaces oxygen from its

Flurprimidol (Cutless, SePro Corp., Carmel, IN)

Figure 2.6. Chemical structure of flurprimidol.

27

Paclobutrazol (Trimmet, Syngenta Chem. Co., Greensboro, NC)

Figure 2.7. Chemical structure of paclobutrazol

Figure 2.8. Type II PGRs, flurprimidol and paclobutrazol, inhibiting the enzyme kaurene

oxidase from converting ent-kaurene (a) to ent-kaurenoic (b) acid in plant gibberellin

biosynthesis.

binding site at the protoheme iron inhibiting ent-kaurene oxidation (Figure 2.8)

(Rademacher, 2000). Unlike TE, paclobutrazol and flurprimidol are root absorbed rather

A B

28

than foliar absorbed. These two PGRs are most commonly used for annual bluegrass

(Poa annua L.) suppression (Woosley et al., 2003; Bell et al., 2004; Bigelow et al.,

2007). However, for Kentucky bluegrass, Stier et al. (1999) reported two flurprimidol

applications applied at treatment initiation and again at week 6 at a sub-label rate (0.56 kg

ha-1

) maintained acceptable TQ for 100 days when grown under 1.7 mol m-2

of light. A

rate higher than label recommendations (2.8 kg ha-1

) caused phytotoxicity.

Cultural Practices

The cornerstone of turfgrass management is sound agronomic practices. Three

essential turfgrass cultural practices are nutrition, water, and mowing. Appropriate

management of these cultural practices is vital for a healthy, vigorous turfgrass stand,

especially in an unfavorable microenvironment, such as reduced light. Sound agronomic

practices can mask and at times, improve turfgrass response when environmental stresses

exist. In shade, appropriate PGR use, N, and mowing practices can minimize negative

effects of tree shade. In addition, selection of turfgrass species and cultivars adapted to

shade is also a vital management decision (Tables 2.1 and 2.2).

Trinexapac-ethyl application

The goal of a turfgrass manager is to reduce clipping yield while maintaining

optimal quality. Therefore, use of the GA20 to GA1 biosynthesis inhibiting PGR, TE, has

become a routine cultural management practice to reduce mowing frequency. However,

TE has recently been investigated as a possible environmental stress reducing PGR

(Heckman et al., 2001 a and b; Richardson, 2002; Baldwin et al. 2006). In particular, TE

29

enhances TQ when applied to shade grown turfgrasses (Stier and Rogers, 2001; Goss et

al., 2002; Steinke and Stier, 2003; Tegg and Lane, 2004b; Bunnell et al., 2005b).

In shade, GA1 and GA20 production increased 47% and 30%, respectively, in

Kentucky bluegrass cultivars (Tan and Qian, 2003). This GA increase caused unwanted

excessive vertical shoot growth rapidly depleting plant carbohydrate status. Excessive

shoot growth also leads to scalping and turfgrass thinning. Turfgrass managers prefer a

dense uniform turfgrass while minimizing shoot growth. Since TE reduced GA1

production by 49% (Tan and Qian, 2003), TE is an effective management tool to combat

unfavorable shaded microenvironments often found on golf courses.

Recent studies have shown TE to be an effective management tool to enhance warm-

season turfgrass growth and development in shade. Bunnell et al. (2005b) noted TifEagle

bermudagrass grown in 4 hours of sunlight showed greater TQ scores and chlorophyll

concentration with tri-weekly TE applications (0.0393 kg a.i. ha-1

) along with

an increase in mowing height (4.7 mm). Diamond zoysiagrass (Zoysia matrella (L.)

Merr.) grown under 86% shade with monthly (0.048 kg a.i. ha-1

) and bimonthly (0.096 kg

a.i. ha-1

) TE applications significantly enhanced TQ, root production, root + rhizome

tissue TNC, and photosynthetic efficiency (Qian and Engelke, 1999a). Similarly, Qian et

al. (1998) demonstrated TE prolonged Diamond zoysiagrass acceptable TQ (>6) for 134

more days compared to nontreated under 88% shade. Also, TE treated turf had 113%

greater TNC and 50% greater canopy photosynthetic rate compared to nontreated (Qian

et al., 1998).

30

Table 2.1. Comparison of 31 turfgrasses shade adaptation (Beard, 2005)

Relative Comparison Turfgrass Scientific Name

Excellent fine-leaf fescue Festuca spp.

wood bluegrass Poa nemoralis

St. Augustinegrass

Stenotaphrum

secundatum

rough bluegrass Poa trivialis

Kikuyugrass

Pennisetum

clandestinum

Creeping bentgrass Agrostis stolonifera

supina bluegrass Poa supine

Good tufted hairgrass Deschampsia caepitosa

annual bluegrass Poa annua var. annua

Creeping bentgrass Agrostis stolonifera

tall fescue Festuca arundinacea

velvet bentgrass Agrostis canina

crested hairgrass Koeleria macrantha

colonial bentgrass Agrostis capillaris

manila zoysiagrass

Zoysia matrella var.

matrella

Japanese zoysiagrass Zoysia japonica

Mascarene zoysiagrass

Zoysia matrella var.

tenuifolia

Medium redtop bentgrass Agrostis gigantean

meadow fescue Festuca pratensis

Canada bluegrass Poa compressa

Centipedegrass Eremochloa ophiuroides

tropical Carpetgrass Anoxopus compressus

crested dog's-tailgrass Cynosurus cristatus

Poor common Carpetgrass Anoxopus fissifolius

perennial ryegrass Lolium perenne

Seashore paspalum Paspalum vaginatum

Bahiagrass Paspalum notatum

Very-poor

annual ryegrass Lolium multiflorum

Kentucky bluegrass Poa pratensis

Bermudagrasses Cynodon spp.

American Buffalograss Buchloe dactyloides

31

Table 2.2. Classification of 42 bermudagrass cultivars relative shade tolerance (adapted from

Baldwin et al., 2008).

Relative

Comparison Cultivar Propagation Scientific Name

Excellent Celebration Vegetative Cynodon dactylon x C. transvaalensis

Very-Good TiftNo.4 Vegetative C. dactylon x C. transvaalensis

TiftNo.1 Vegetative C. dactylon x C. transvaalensis

Transcontinental Seeded

Cynodon dactylon (L.) Pers. var.

dactylon

Good SWI-1003 Seeded C. dactylon (L.) Pers. var. dactylon

Sunbird Seeded C. dactylon (L.) Pers. var. dactylon

Intermediate Aussie Green Vegetative C. dactylon x C. transvaalensis

MS-Choice Vegetative C. dactylon x C. transvaalensis

Princess 77 Seeded C. dactylon (L.) Pers. var. dactylon

SWI-1045 Seeded C. dactylon (L.) Pers. var. dactylon



Fair B-14 Seeded C. dactylon (L.) Pers. var. dactylon

Riviera Seeded C. dactylon (L.) Pers. var. dactylon


TiftNo.3 Vegetative C. dactylon x C. transvaalensis

Southern Star Seeded C. dactylon (L.) Pers. var. dactylon

TiftNo.2 Seeded C. dactylon (L.) Pers. var. dactylon

Poor Sunstar Seeded C. dactylon (L.) Pers. var. dactylon


FMC-6 Seeded C. dactylon (L.) Pers. var. dactylon

Mohawk Seeded C. dactylon (L.) Pers. var. dactylon


Tifway Vegetative C. dactylon x C. transvaalensis

Midlawn Vegetative C. dactylon x C. transvaalensis

TifSport Vegetative C. dactylon x C. transvaalensis

Premier Vegetative C. dactylon x C. transvaalensis

Ashmore Vegetative C. dactylon x C. transvaalensis

CIS-CD5 Seeded C. dactylon (L.) Pers. var. dactylon



Panama Seeded C. dactylon (L.) Pers. var. dactylon

La Paloma Seeded C. dactylon (L.) Pers. var. dactylon

Yukon Seeded C. dactylon (L.) Pers. var. dactylon

OKC 70-18 Vegetative C. dactylon x C. transvaalensis

NuMex Sahara Seeded C. dactylon (L.) Pers. var. dactylon

32

Table 2.2. Classification of 42 bermudagrass cultivars relative shade tolerance (adapted from

Baldwin et al., 2008) (continued).

Very-poor SWI-1014 Seeded C. dactylon (L.) Pers. var. dactylon

GN-1 Vegetative C. dactylon x C. transvaalensis

Patriot Vegetative C. dactylon x C. transvaalensis

Sundevil Seeded C. dactylon (L.) Pers. var. dactylon

SR 9554 Seeded C. dactylon (L.) Pers. var. dactylon

Arizona

Common Seeded C. dactylon (L.) Pers. var. dactylon

Nitrogen

Nitrogen is the most dynamic and important nutrient for turfgrasses. Nitrogen

provides color, density, recuperative ability, and plant health when applied at adequate

rates. It has long been associated that a reduction of N input will enhance a turfgrass

stand when light interception is limited. Burton et al. (1959) reported high N (726 kg ac-

1) in 64% shade decreased „Coastal‟ bermudagrass carbohydrates by 30% and decreased

plant density and leaf area compared to low N (90 kg ac-1

). Bunnell et al. (2005b) also

noted a 39% reduction in TNC in heavily shaded TifEagle bermudagrass with additional

N (24.5 kg ha-1

(NH4)2SO4). Stanford et al. (2005) noted Tifdwarf bermudagrass

internode and leaf length significantly increased when photosynthetic photon flux density

(PPFD) was reduced from 975 to 300 mol m-2

s-1

. Also, applying Tifdwarf

bermudagrass with N at 8.1 kg ha-1

wk-1

vs. 24.4 kg ha-1

wk-1

significantly reduced leaf

length, internode length, and above ground dry matter (Stanford et al., 2005). Therefore,

reduced N rates should enhance performance in shade by reducing above ground vertical

growth.

33

Schmidt and Blaser (1967) reported „Cohansey‟ bentgrass net photosynthesis

declined along with reduced growth when fertilized with 1.0 kg N per 200 m2 every 10 to

20 days. Bell and Danneberger (1999a) stated Penncross creeping bentgrass quality was

enhanced with no N input rather than 0.11 kg urea N month-1

. Similarly, Goss et al.

(2002) reported Penncross creeping bentgrass turf cover reduced 16% with high liquid N

fertilization when grown in 80% shade.

To date, only one study has been conducted to determine the influence of N, N

type, and combination of TE and N on the performance of turfgrass in shade. Steinke and

Stier (2003) evaluated „Supranova‟ supine bluegrass, „Nuglade‟, 25% mix of „Rugby II‟,

„Kelly‟, and „NuBlue‟ Kentucky bluegrass, and Penncross creeping bentgrass response to

80% light reduction. TE applications of 0.05 kg a.i. ha-1

in 28 and 58 day intervals along

with water soluble urea as granular or liquid (12 kg N ha-1

) in 14 day intervals was

evaluated. Trinexapac-ethyl significantly enhanced all species TQ and chlorophyll in

shade. Liquid applications increased chlorophyll concentration compared to granular N

form. Nitrogen source did not affect leaf N content in creeping bentgrass. In general, fall

liquid N application was best, while granular N source was best for summer TQ.

While studies have clearly indicated reducing N in shaded environments is

beneficial, research in this area is still lacking. In particular, does N source (liquid or

granular) or combination of N sources allow bermudagrass to perform more efficiently

under shade stress? Also, will the use of TE interacting with low N rates allow a

turfgrass manager to further reduce N input in a shaded environment without a

compromise in TQ? Also, the effect of mowing height in combination with TE and N

34

source has not been investigated on warm-season species. Much of the research on N

source has focused on cool-season turfgrasses.

Mowing

Mowing height is a critical management practice for a successful turfgrass stand

grown in shade. With the release of new ultradwarf bermudagrass cultivars such as

TifEagle (Hanna and Elsner, 1999), „MiniVerde‟ (Turfgrass America Co., Granbury,

TX), „MS-Supreme‟ (Krans et al., 1999), Floradwarf (Dudeck and Murdoch, 1998), and

Champion (Brown et al., 1997), superintendents maintain daily mowing heights as low as

2.5 mm to allow for player expected green speeds. A higher mowed turfgrass enhances

leaf sunlight capture ability, turfgrass density, and increases root depth (Dudeck and

Peacock, 1992). Therefore, a raise in the height of cut should enhance shade-tolerance by

allowing a greater leaf surface for solar absorption.

Recent studies have investigated the effect raising mowing heights have on

bermudagrass response when grown in shade. A TifEagle bermudagrass green

receiving 4 hours of sunlight mowed at 4.7 mm had greater TQ and chlorophyll

concentration than the 2.5 mm mowing height maintained with 4 hours of sunlight

(Bunnell et al., 2005b). However, after 8 weeks of receiving 4 hours of sunlight, TNC

were reduced from 26.28 to 17.95 mg g-1

by raising mowing heights (Bunnell et al.,

2005b). Increased mowing heights for TifEagle, Champion, Tifdwarf, Floradwarf, and

Reesegrass bermudagrass had little effects on root biomass, however, a 4 mm mowing

height significantly improved net photosynthetic rates compared to 3 mm mowing

height (Miller and Edenfield, 2002). Also, Ries et al. (2002) noted „De Anza‟

35

zoysiagrass performed optimally in shade when mowing heights were 24 mm rather

than 12 mm.

36

CHAPTER III

PHYSIOLOGICAL AND MORPHOLOGICAL RESPONSES OF 42

BERMUDAGRASS CULTIVARS

Introduction

Bermudagrass continues to be the dominate warm-season turfgrass in warm

climatic regions of the world (Shearman, 2006). Its drought tolerance, recuperative

ability, salt tolerance, wear tolerance, aggressive stoloniferous and rhizomatous growth

habit, and overall appearance make bermudagrass an ideal turfgrass in many

environments. Although bermudagrass cultivars possess such characteristics,

bermudagrass breeding programs continue to produce new and improved cultivars.

Recently, bermudagrass breeding has produce cultivars with improved characteristics,

such as enhanced cold (Martin et al., 2007) and shade tolerance (Hanna and Maw, 2007).

Previous recent investigations have noted bermudagrass diversity among

experimental, standard, and new commercially available bermudagrass cultivars for traits

such as freeze tolerance (Anderson et al., 2007), cold tolerance (Munshaw et al., 2006),

drought tolerance (Baldwin et al., 2006), shade tolerance (Jiang et al., 2004; Bunnell et

al., 2005c; Baldwin et al., 2008; and divot recovery potential (Karcher et al., 2005).

However, few studies have provided detailed morphological and physiological

characteristics of new, experimental, and industry standard field-grown bermudagrass

cultivars.

Parameters used to access selected turfgrasses in the National Turfgrass

Evaluation Program (NTEP) typically include turfgrass quality (TQ), color, percent

37

spring green-up (SGU), percent dormancy, disease/insect occurrence, winterkill,

establishment rates, leaf texture, and density. However, parameters often excluded

include carbohydrate status, root biomass, shoot biomass, thatch accumulation, and

chlorophyll. These types of parameters would be invaluable to many within the turfgrass

industry including sod producers, sports field managers, golf course superintendents,

extension personnel, and plant breeders. While many new commercially available

bermudagrass cultivars exist, few studies have examined morphological and

physiological characteristics of these new cultivars. Therefore, objective of this research

was to evaluate and compare spring, summer, and fall performance of new and

experimental bermudagrass cultivars with current bermudagrass industry standards.

Materials and Methods

A two-year research project was conducted in 2006 and 2007 at the Clemson

University Turfgrass Research Center, Clemson, SC, 2002 bermudagrass National

Turfgrass Evaluation Program (NTEP) trials (Table A.1) (Illustration D.2). The 42

bermudagrass cultivars were planted summer, 2002 on a native clayey soil. Cultivars

were provided N at a rate of 24.4 kg ha-1

in May and September, while a N rate of 48.8

kg ha-1

was applied in June, July, and September using a complete fertilizer (16N-1.7P-

6.6K) with a slow release urea and micronutrients (kg ha-1

): Calcium, 6; Magnesium, 3;

Sulfur, 9; Boron, 0.06; Copper, 0.03; Iron, 0.3; Manganese, 0.15; Molybdenum, 0.0015;

and Zinc, 0.15. Mowing was performed three to four times weekly throughout the

growing season at a height of 1.27 cm. Irrigation was provided as needed to prevent

38

drought stress and/or wilt. Glyphosphate was sprayed in the winter over all cultivars at a

rate of 4.6 L ha-1

. Otherwise, no other pesticides, herbicides, or fungicides were provided

during the duration of the study. Also, no core aerification or topdressing program

occurred.

Data collection

Data collection included visual TQ, SGU, percent dormancy, total shoot

chlorophyll, clipping yield, thatch accumulation, root total non-structural carbohydrates,

and total root biomass.

TQ was visually rated weekly and then averaged for each month from May

through October. TQ ratings were based on color, density, texture, and uniformity of the

bermudagrass surface and rated from 1 to 9, 1 = brown, dead turfgrass, 6 = minimal

acceptable turfgrass, 9 = perfect green, healthy turfgrass.

Spring green-up was visually rated every three to four days once green tissue

emerged using a scale of 0 -100% with 0% = complete brown turfgrass and 100% =

complete green turfgrass. Similarly, percent dormancy was visually rated every three to

four days once bermudagrass cultivars started to enter dormancy using a scale of 0 -100%

with 0% = complete green turfgrass and 100% = complete brown turfgrass.

Total shoot chlorophyll (mg g-1

) was measured in mid-May, mid-July, and mid-

September eath year. Fresh clippings (minimum 0.1g) were collected from each plot and

placed in a plastic bag inside a covered bucket to prevent sunlight degradation. A 0.1 g

of clipping from each plot was placed in a glass test tube (1.0 cm in width and 14.8 cm in

length) with 10 mL of dimethyl sulfoxide (DMSO), which eliminates shoot tissue

39

grinding to extract chlorophyll (Hiscox and Israelstam, 1979). Samples were incubated

in 65 oC water on a hot plate (PC-600, Corning, Corning, NY) for 1.5 hr and continuously

shaken. Upon completion, samples were passed through filter paper (Whatman 41,

Whatman, England) and remaining extract (2 mL) transferred into cuvettes. Absorbance

values were recorded at 663 nm and 645 nm wavelengths using a spectrophotometer

(GenesysTM

20, ThermoSpectronic, Rochester, NY). Blanks were initially run and also

after every sixth sample. The following formula was used to calculate total shoot

chlorophyll: (mg g-1

) = (8.02 * D663 + 20.2 * D645) * 0.1 (Arnon, 1949).

Clipping yield (g m-2

) was collected in mid-May, mid-July, and mid-September

for both years. Shoot tissue was collected using a walk behind greens mower

(Greenmaster® 800, The Toro Company, Bloomington, MN) following two days of

growth. Following clipping collection, clippings were oven dried at 80oC for 48 hr and

weighed to quantify shoot production.

Thatch accumulation (g) was measured in mid-May, mid-July, and mid-

September for both years. A bulk density sampler extracted one 154.4 cm3 core from

each plot. Roots were clipped at the base of the thatch layer and the remaining thatch

sample was placed in an 80oC oven for 96 hrs and weighed. Thatch samples were then

placed in a muffle furnace (Benchtop Muffle Furnace LMF-A550, Omega Engineering,

Inc., Stamford, CT) at 525oC for three hrs to provide ash organic weight (Snyder and

Cisar, 2000). Samples were weighed again and then subtracted from the original dry

weight, which determined thatch accumulation (g).

40

Root TNC (mg g-1

) was analyzed mid-May and mid-July for both years. Root

tissue was harvested using a bulk density sampler which extracted 154.4 cm3 (10.2 cm in

depth) cores prior to sunrise to minimize any diurnal fluctuations. Following soil

removal, root tissue samples were stored at -75oC until freeze dried at -40

oC for two wks

to cease all metabolic activity. Samples were then ground using an A-10 plant grinder

(IKA Works, Inc., Wilmington, NC). Grounded samples were rehydrated with 100 L of

80% ethanol (EtOH) and 2 mL of 0.1 M sodium acetate buffer (pH 4.5) in glass test tubes

13 X 100 mm. Rehydrated samples were placed in boiling water for 1 hr, cooled for 1 hr

and repeated. Then, 2 mL of invertase (Sigma I-4753, 433 units mg-1

) and

amyloglucosidase (Sigma A-7255, 23,000 units g-1

) were added to solution. Samples

were placed in water bath (40 – 45oC) for three days and vortexed three times daily.

TNC analysis was analyzed using Nelson‟s Assay (1944), which determines glucose and

fructose in plant tissue (Nelson, 1944; Somogyi, 1945). A 25 L aliquot was removed

and two reagents (copper and arsenomolybdate) were added to solution. Absorbance

values were measured at 520 nm using a spectrophotometer (GenesysTM

20,

ThermoSpectronic, Rochester, NY).

Roots were extracted from the soil using a cylinder core sampler (7.5 cm in diam.

by 30 cm deep) end of May, July, and September for both years to determine total root

biomass. Once all soil was completely removed from each soil plug using tap water,

roots were clipped from the thatch base and placed in an oven (80.0 oC) for 48 hr, then

weighed. Following oven drying, roots were placed in a muffle furnace (Benchtop

Muffle Furnace LMF-A550, Omega Engineering, Inc., Stamford, CT) at 525oC for three

41

hrs to provide ash organic weight (Snyder and Cisar, 2000). Samples were weighed

again and then subtracted from the original dry weight, which determined total root

biomass (g).

Data Analysis

Treatments were arranged in a randomized complete block design with three

replications. All statistical computations were conducted using the Statistical Analysis

System (version 9.1, SAS Institute, Cary, NC). Initially, means were separated by

Fisher‟s Least Significant Difference (LSD) to determine the statistically ( ≤ 0.05) best

performing cultivar. Then, Dunnett‟s test (Dunnett, 1955) was used to compare all other

cultivars with the statistically best cultivar. Year by treatment interaction occurred for

SGU ratings and total root biomass in July; therefore, data are presented and evaluated

separately for each year. A year by treatment interaction was not noted for other

parameters; therefore, yearly data were pooled. Significant differences were not detected

for root TNC in May and July; therefore, data is not presented.

Results and Discussion

Spring Green-up

Year I

Celebration was the only cultivar in the top statistical category for all SGU rating

dates in year I (Table 3.1). Percent green tissue emergence on 20 March 2006 was

highest for Celebration (21%), MS-Choice (11%), SWI-1014 (11%), and GN-1 (11%).

By 6 April 2006, Celebration (76%), Aussie Green (48%), and Riviera (53%) had

42

Table 3.1. Spring green-up (SGU) of 42 bermudagrass cultivars rated from 20 March

to 21 April 2006 at Clemson University, Clemson, SC.

Spring Green-Up†

Cultivar 3/20/06 4/3/06 4/6/06 4/10/06 4/14/06 4/18/06 4/21/06

Celebration 21* 55* 76* 75* 81* 100* 100*

Aussie Green 3 18 48* 66* 83* 100* 100*

MS-Choice 11* 21 31 48* 63* 90* 98*

Riviera 8 25 53* 66* 80* 93* 100*

SWI-1014 11* 18 26 40* 56* 73* 78*

CIS-CD6 3 11 25 40* 60* 80* 95*

FMC-6 1 10 33 36* 53* 66* 85*

GN-1 11* 30 43 16 63* 86* 90*

La Paloma 3 8 16 33* 56* 66* 76*

Southern Star 1 15 23 46* 61* 73* 90*

Sunbird 6 21 33 50* 53* 81* 90*

SWI-1001 3 23 23 46* 71* 88* 96*

SWI-1003 5 21 33 56* 76* 93* 100*

SWI-1012 1 8 21 40* 45* 80* 93*

SWI-1041 3 15 31 53* 58* 83* 90*

SWI-1044 8 28 35 61* 63* 85* 96*

SWI-1045 1 10 20 40* 71* 83* 100*

SWI-1046 3 18 28 66* 71* 95* 100*

TiftNo.1 3 6 18 36* 65* 93* 100*

TiftNo.2 5 11 36 53* 66* 90* 100*

Transcontinental 1 8 15 31 46* 76* 93*

Yukon 1 8 13 36* 56* 78* 96*

Arizona Common 3 11 13 28 48* 66* 83*

B-14 3 11 21 25 36* 60* 83*

CIS-CD5 1 6 8 20 38* 40 73*

NuMex Sahara 3 16 16 31 46* 73* 86*

Panama 1 13 13 43* 46* 56 81*

Patriot 0 5 8 18 43* 86* 100*

Princess 77 3 18 25 60* 73* 55 93*

SR 9554 3 5 15 26 50* 56* 76*

Sundevil 1 10 23 30 60* 73* 90*

Sunstar 0 11 13 33* 28 56* 83*

TiftNo.3 1 6 18 26 46* 80* 98*

TiftNo.4 1 8 15 20 41* 76* 93*

CIS-CD7 1 5 13 25 45* 55 73*

Midlawn 0 5 6 8 21 56* 90*

OKC 70-18 1 3 5 8 26 76* 96*

Tifsport 0 5 6 16 30 63* 98*

Tifway 0 5 6 13 25 70* 100*

Ashmore 0 5 10 20 26 48 73*

43

attained greater SGU compared to other cultivars. Cultivars with slowest SGU were CIS-

CD5, Patriot, Midlawn, OKC 70-18, Tifsport, Tifway, and Premier with an average SGU

rating of 7% on 6 April 2006. Riviera showed 112% (6 April 2006) and 69% (18 April

2006) greater SGU than Princess 77. Also, Rivera showed a 7.8 (6 April 2006), 4.1 (10

April 2006), and a 2.2 (14 April 2006) unit SGU increase compared to Tifway

(Illustration D.3). Munshaw et al. (2006) reported similar results in a field study as

Riviera showed significantly quicker SGU than Princess 77 and Tifway bermudagrass.

By 18 April 2006, Celebration and Aussie Green were the first cultivars to reach 100%

SGU, closely followed by Riviera (93%), SWI-1003 (93%), TiftNo.1 (93%), MS-Choice

(90%), and TiftNo.2 (90%). On the same rating date, CIS-CD5 (40%), Princess 77

(55%), CIS-CD7 (55%), Panama (56%), Ashmore (48%), Premier (46%), and Mohawk

(43%) showed significantly slower SGU ratings compared to other cultivars. On 21 April

2006, all cultivars, except Mohawk (68%), had SGU ratings greater than 70%.

Year II

Midlawn and Premier were the only cultivars in the top statistical category for all

SGU ratings in 2007 ( Illustration D.4) (Table 3.2). However, both of these cultivars had

slow SGU ratings in 2006. This yearly variation may have occurred due to differences in

Table 3.1. Spring green-up (SGU) of 42 bermudagrass cultivars rated from 20 March to

21 April 2006 at Clemson University, Clemson, SC (continued).

Premier 0 3 8 8 28 46 71*

Mohawk 1 6 11 13 35 43 68

*Mean different from the statistically best cultivar using Dunnett‟s test ( = 0.05). †Spring green-up based on a scale of 0-100%, 0% = complete brown bermudagrass, 100% =

complete green bermudagrass.

44

Table 3.2. Spring green-up (SGU) of 42 bermudagrass cultivars rated from 20

March to 21 April 2007 at Clemson University, Clemson, SC.

Spring Green-Up†

Cultivar 3/22/07 3/29/07 4/2/07 4/5/07 4/13/07 4/20/07 4/27/07 Midlawn 16* 66* 90* 93* 51* 93* 98*

Premier 38* 83* 88* 95* 58* 86* 100*

SWI-1003 21* 56* 70* 83* 30 63* 95*

SWI-1012 10 56* 80* 90* 43* 68* 91*

SWI-1041 21* 56* 75* 80* 38 75* 85*

SWI-1045 15 50* 75* 86* 48* 75* 95*

TiftNo.4 15 41* 73* 81* 51* 70* 98*

Transcontinental 28* 60* 71* 73* 32 70* 96*

Aussie Green 31* 70* 90* 93* 33 56 98*

Celebration 23* 78* 85* 93* 36 55 91*

CIS-CD6 17 50* 80* 88* 30 60* 90*

GN-1 23* 66* 65* 73* 16 50 93*

NuMex Sahara 18 55* 63* 76* 27 61* 88*

OKC 70-18 5 22 73* 83* 68* 75* 96*

Patriot 5 40 86* 96* 68* 88* 100*

Riviera 18 51* 91* 96* 35 70* 98*

Southern Star 12 56* 66* 73* 17 60* 88*

SR 9554 15 50* 66* 85* 30 60* 93*

SWI-1001 25* 63 81* 83* 30 80* 96*

SWI-1014 15 45* 75* 83* 32 73* 96*

SWI-1046 13 60* 86* 95* 35 80* 96*

TiftNo.1 10 46* 63* 85* 17 60* 98*

Yukon 10 40 83* 91* 58* 83* 100*

Arizona

Common 8 38 60* 66* 20 60* 83*

FMC-6 10 33 55* 70* 17 58* 90*

MS-Choice 15 44* 70* 75* 20 46 86*

Princess 77 15 45* 60* 83* 35 55 86*

SWI-1044 13 56* 68* 81* 25 53 76*

Tifsport 8 35 61* 76* 37 75* 98*

TiftNo.3 15 43* 81* 88* 13 55 90*

Ashmore 7 30 61* 70* 35 53 86*

Sunbird 17 37 61* 73* 20 51 78*

Sunstar 12 32 60* 73* 18 55 81*

B-14 18 48* 50 63* 15 46 70

CIS-CD7 8 35 53* 65* 13 41 75

Sundevil 10 30 52 58 28 63* 78*

TiftNo.2 8 42 50 70* 13 46 95*

Panama 12 28 35 63* 10 35 56

45

Table 3.2. Spring green-up (SGU) of 42 bermudagrass cultivars rated from 20

March to 21 April 2007 at Clemson University, Clemson, SC (continued). CIS-CD5 7 17 30 43 12 35 73

La Paloma 5 28 33 53 13 33 68

Mohawk 7 28 50 60 17 53 73

*Mean different from the statistically best cultivar using Dunnett‟s test ( = 0.05). †Spring green-up based on a scale of 0-100%, 0% = complete brown bermudagrass,

100% = complete green bermudagrass.

air temperature for each spring (Table 3.3). In 2007, the maximum air

temperature was 12oC and 8

oC warmer from 20 March to 3 April compared to

2006. Similarly, in 2007, the minimum air temperature was 7oC and 8

oC warmer

from 20 March to 3 April compared to 2006. However, in 2006, greater

precipitation was noted than in 2007 throughout the spring, however, rainfall

totals were well below historical averages (data not shown). It is commonly

accepted that optimal temperature and soil moisture are critical requirements for

Table 3.3. Average weekly maximum/minimum air temperatures (oC) and

precipitation (cm) from 20 March to 27 April 2006 and 2007 in Clemson

University, Clemson, SC.

Maximum

Temperatures (oC)

Minimum

Temperatures (oC)

Precipitation

(cm)

2006 2007 2006 2007 2006 2007

Week 1† 11 23 2 9 0.60 0.00

Week 2 17 25 5 13 0.10 0.10

Week 3 26 21 8 6 0.30 0.10

Week 4 24 17 7 6 0.30 0.02

Week 5 27 23 14 7 0.60 0.00

Week 6 28 27 13 12 0.00 0.00 †Week 1 begins on 20 March for 2006 and 2007.

46

successful bermudagrass spring transition. Based on this research, it appears air

temperature or soil moisture may be of greater importance for bermudagrass cultivar

SGU, depending on the selected cultivar. Future research is warranted to further

elucidate whether air temperature or soil moisture is more critical for enhancing SGU.

On 5 April 2007, Sundevil, CIS-CD5, La Paloma, and Mohawk showed SGU delay

(<13%) compared to all other cultivars, while Premier, Patriot, Riviera, and SWI-1046

had SGU rating ≥95%. In Clemson, SC, from 6 April to 10 April, average minimum air

temperatures were below 0.6oC, therefore, many cultivars SGU was temporarily

inhibited. However, OKC 70-18 and Patriot were able to retain >60% green color,

despite the late freeze. This can most likely be directly attributed to their improved cold

hardiness relative to other bermudagrasses since the cold temperatures minimally

impacted SGU (Anderson et al., 2007). These cultivars may continue to find a market in

the transition zone if late freezes become a common occurrence. On the other hand,

cultivars most sensitive (<15% SGU) to the late freeze were TiftNo.3, CIS-CD7,

TiftNo.2, Panama, CIS-CD5, and La Paloma. Even with the late freeze, winterkill was

not observed for any cultivars. Only Midlawn was able to maintain SGU >90% by 20

April 2007. B-14 (70%), CIS-CD7 (75%), Panama (56%), CIS-CD5 (73%), La Paloma

(68%), and Mohawk (73%) were the only cultivars to have SGU less than 80%, while

Premier, Patriot, Tifway, and Yukon were the only cultivars to reach 100% by 27 April

2007.

While bermudagrass is considered a durable turfgrass, it is a fragile plant when

transitioning from winter dormancy into an emerging green tissue state in early spring.

47

Therefore, spring is perhaps the most critical season to optimize bermudagrass growth

and performance in preparation for the summer peak growing season in the transition

zone. Cultivars with enhanced SGU may be a very desirable trait among

bermudagrasses. However, a late freezing frost may potentially cause increased freeze

damage. Therefore, cultivars in this study with enhanced SGU may or may not be a

desirable trait depending on location.

May Performance

OKC 70-18 and SWI-1046 placed in the top statistical group for each parameter

measured in May, while CIS-CD5, GN-1, and Princess 77 placed in the top statistical

group one time during May (Table 3.4). Ashmore, B-14, CIS-CD7, Panama, Sunstar,

Arizona Common, La Paloma, Mohawk, NuMex Sahara, SR 9554, and CIS-CD5 were

the only cultivars to drop below acceptable threshold of 6 for TQ in May. Cultivars with

highest TQ scores (≥7.5) were SWI-1046, Celebration, Tifway, and TiftNo.4. MS-

Choice, SWI-1041, TiftNo.4, CIS-CD5, and Princess 77 produced significantly less

clipping yield (≤3.2 g) compared to other cultivars. Meanwhile, TifSport, Tifway,

Southern Star, and Arizona Common were the only cultivars to produce >6 g of

clippings. Lowest chlorophyll concentration was noted for Ashmore (1.45 mg g-1

), while

Celebration produced highest concentration of 3.01 mg g-1

. Industry standards, Tifway

and TifSport, produced 2.72 and 2.88 mg g-1

of chlorophyll, respectively. Cultivars with

greatest root biomass (>0.70 g) included Celebration (0.89 g), MS-Choice (0.75 g), SWI-

1014 (0.72 g), and SWI-1046 (0.72 g), while Premiere (0.27 g), Patriot (0.22 g), Arizona

48

Table 3.4. Turfgrass quality, clipping yield, shoot chlorophyll, total root

biomass, and thatch accumulation of 42 field-grown bermudagrass cultivars

at Clemson University in May, 2006 and 2007.

Cultivar

Turfgrass

Quality†

Clipping

Yield

(g)

Shoot

Chlorophyll

(mg g-1

)

Root

Biomass

(g)

Thatch

(g)

OKC 70-18 7.1* 5.58* 2.37* 0.50* 8.2*

SWI-1046 7.5* 5.43* 2.48* 0.72* 8.4*

Celebration 7.7* 4.31* 3.01* 0.89* 9.9

Midlawn 7.1* 7.39* 2.83* 0.38 6.8*

Premier 7.0* 4.62* 2.81* 0.27 8.4*

Patriot 7.3* 4.20* 2.37* 0.22 8.0*

SWI-1003 7.0* 4.31* 2.59* 0.49* 8.7

SWI-1045 7.3* 4.94* 2.74* 0.8* 10.8

TiftNo.1 7.2* 4.65* 2.71* 0.68* 8.7

TiftNo.2 7.1* 3.54* 2.88* 0.68* 9.0

TiftNo.3 6.8 4.39* 2.77* 0.67* 8.5*

Ashmore 5.8 4.76* 1.45 0.47* 7.7*

Aussie Green 7.4* 4.44* 2.52* 0.30 12.3

B-14 5.2 3.76* 1.89 0.52* 7.4*

CIS-CD7 5.8 3.89* 2.13 0.47* 8.2*

Panama 5.2 3.98* 1.69 0.48* 7.3*

Sunbird 6.4* 5.52* 2.07 0.38 8.5*

Sunstar 5.8 4.58* 2.38* 0.38 7.4*

SWI-1044 6.6 4.21* 2.41* 0.69* 9.8

Tifsport 7.4* 6.07* 2.88* 0.42 9.7

Tifway 7.9* 6.21* 2.72* 0.46 12.4

Transcontinental 6.4 5.08* 1.93 0.65* 8.4*

Yukon 6.8 3.88* 2.37* 0.43 7.5*

Arizona

Common 5.8 6.09* 1.87 0.29 6.2*

CIS-CD6 6.4 5.43* 1.83 0.36 7.7*

FMC-6 6.0 4.21* 1.75 0.39 6.9*

La Paloma 5.9 4.96* 2.02 0.35 6.8*

Mohawk 5.3 5.37* 1.93 0.55* 5.6*

MS-Choice 6.1 3.15 2.47* 0.75* 12.8

NuMex Sahara 5.6 5.61* 1.91 0.33 5.0*

Riviera 6.5 5.14* 1.61 0.51* 9.9

Southern Star 6.1 7.39* 1.91 0.47* 8.9

SR 9554 5.8 4.99* 2.08 0.26 6.6*

Sundevil 6.0 4.15* 1.86 0.36 7.4*

SWI-1001 6.9 4.88* 2.17 0.46 7.1*

SWI-1012 6.7 3.85* 2.53* 0.38 8.6

SWI-1014 6.1 5.07* 2.36 0.72* 9.6

49

Table 3.4. Turfgrass quality, clipping yield, shoot chlorophyll, total root

biomass, and thatch accumulation of 42 field-grown bermudagrass cultivars

at Clemson University in May, 2006 and 2007 (continued).

SWI-1041 6.7 3.11 2.61* 0.50 7.9*

TiftNo.4 7.6* 2.94 2.75* 0.32 9.7

GN-1 6.7 4.23* 2.33 0.28 8.8

Princess 77 6.7 3.22 2.13 0.59* 8.7

*Mean different from the statistically best cultivar using Dunnett‟s test

( = 0.05). †Turfgrass quality based on a scale of 1 – 9, 1 = brown/dead turf, 6 =

minimally acceptable turf, 9 = ideal green, healthy turf.

Common (0.29 g), SR 9554 (0.26 g), and GN-1 (0.28 g) produced least (<0.30 g) root

biomass. Baldwin et al. (2006) also reported Celebration produced greater root biomass

than Arizona Common in a greenhouse study. Greater root biomass may lead to

enhanced drought tolerance of these cultivars, however, the relative drought tolerance of

many of these cultivars remains unknown. Due to such rooting variation, large scale

screening of these bermudagrass cultivars for drought tolerance is warranted. Cultivars

with greatest thatch accumulation were MS-Choice (12.8 g), Tifway (12.4 g), and Aussie

Green (12.3 g), while NuMex Sahara (5.0 g) and Mohawk (5.6 g) produced least amount

of thatch

Summer Performance

Turfgrass quality scores of Arizona Common, Ashmore, B-14, CIS-CD5, CIS-

CD7, Mohawk, NuMex Sahara, Panama, Southern Star, Sundevil, and Sunstar were all

below acceptable threshold of 6, while all other cultivars TQ scores were greater than 6 in

June (Table 3.5). Highest TQ scores in July were TiftNo.4 (7.6) and Tifway (7.7), while

50

Table 3.5. Turfgrass quality (TQ) of 42 bermudagrass cultivars rated from

June to August, 2006 and 2007 at Clemson University, Clemson, SC.

Turfgrass Quality†

Cultivar June July August

Aussie Green 7.3 7.3* 7.0*

Celebration 7.7 7.3* 7.5*

SWI-1003 6.9 7.0* 7.5*

SWI-1045 7.3 7.3* 7.1*

SWI-1046 7.5 7.2* 7.1*

Tifsport 7.3 7.3* 6.9*

TiftNo.1 7.4 7.3* 7.1*

TiftNo.2 7.5 7.2* 7.0*

TiftNo.4 7.6 7.6* 7.5*

Tifway 7.8 7.7* 7.0*

Yukon 6.9 6.9* 6.8*

MS-Choice 6.4 6.9* 7.2*

Patriot 7.6 7.0* 7.3*

SWI-1001 7.2 6.8 6.9*

SWI-1041 6.8 7.1* 7.0*

SWI-1044 6.8 7.0* 7.0*

TiftNo.3 7.5 7.1* 6.6

GN-1 6.8 6.6 6.6

Midlawn 7.1 6.1 5.8

OKC 70-18 7.0 6.7 5.9

Premier 7.0 6.6 5.4

Princess 77 6.5 6.8 7.3*

SWI-1012 6.7 6.7 7.3*

Arizona Common 5.7 5.7 5.6

Ashmore 5.8 5.7 5.8

B-14 5.4 5.8 6.0

CIS-CD5 5.9 5.8 6.3

CIS-CD6 6.3 6.2 6.3

CIS-CD7 5.8 6.1 6.4

FMC-6 6.1 6.4 6.3

La Paloma 6.1 6.2 6.5

Mohawk 5.6 5.8 6.2

NuMex Sahara 5.7 5.8 6.0

Panama 5.4 5.6 6.0

Riviera 6.2 6.5 6.4

Southern Star 5.9 5.8 5.8

SR 9554 6.1 5.7 5.7

Sunbird 6.5 5.8 5.9

Sundevil 5.9 6.2 5.8

51

Table 3.5. Turfgrass quality (TQ) of 42 bermudagrass cultivars rated

from June to August, 2006 and 2007 at Clemson University, Clemson, SC

(continued).

Sunstar 5.9 6.1 5.8

SWI-1014 6.4 6.5 6.6

Transcontinental 6.3 6.4 6.6

*Mean different from the statistically best cultivar using Dunnett‟s test ( =

0.05). †Turfgrass quality based on a scale of 1 – 9, 1 = brown/dead turf, 6 =

minimally acceptable turf, 9 = ideal green, healthy turf.

Panama‟s TQ score was lowest (5.6). Hanna and Maw (2007) reported TiftNo.4 to have

a dark green color, which may also provide insight into its relative shade-tolerance. By

August, most TQ scores were near or above the acceptable threshold (>6). Highest TQ

scores were noted for Celebration (7.5), SWI-1003 (7.5), TiftNo.4 (7.5), Patriot (7.3),

Princess 77 (7.3), and SWI-1012 (7.3) in August.

Only TiftNo.2 placed in the top statistical category for all parameters measured in

July, 2006 and 2007 (Table 3.6). In July, Tifsport (2.70 mg g-1

), SWI-1046 (2.68 mg g-1

),

SWI-1045 (2.51 mg g-1

), and Tifway (2.51 mg g-1

) had highest chlorophyll

concentrations, while Mohawk (1.72 mg g-1

), B-14 (1.73 mg g-1

), and Arizona Common

(1.83 mg g-1

) showed lowest chlorophyll concentrations. TiftNo.2, Tift.No.1, SWI-1046,

Tifway, Midlawn, and TiftNo.4 produced the greatest amount of clipping yield (>11.5 g)

compared to other cultivars, while MS-Choice (3.93 g) and Riviera (4.26 g) had lowest

clipping yield values. Depending on the type of area where the bermudagrass is to be

used (i.e., lawn, sports field, golf course or rough area), high or low clipping yield

production may or may not be a desirable characteristic. TiftNo.2 and TiftNo.3 produced

52

Table 3.6. Shoot chlorophyll, clipping yield, root biomass, and thatch

accumulation of 42 field-grown bermudagrass cultivars at Clemson University in

July, 2006 and 2007.

Cultivar

Chlorophyll

(mg g-1

) Clipping Yield (g)

Root Biomass

(g)

Thatch

(g)

Year I Year II

TiftNo.2 2.28* 13.43* 1.03* 11.91* 8.61

TiftNo.1 2.45* 14.85* 0.75 14.98* 12.23

SWI-1046 2.68* 11.83* 0.86 11.65* 13.88

Tifway 2.51* 16.98* 0.55 15.51* 14.42

TiftNo.3 2.12* 8.64 1.62* 6.33 10.77*

SWI-1044 2.23* 10.18 0.69 9.51* 10.91*

SWI-1003 2.12* 8.38 0.71 10.43* 11.49*

OKC 70-18 2.11* 11.31 0.55 10.72* 11.49*

Midlawn 2.14* 14.01* 0.38 13.21* 8.94*

TiftNo.4 2.36* 13.01* 0.48 7.92 12.68

CIS-CD5 2.07* 5.65 0.48 3.84 10.01*

SWI-1041 2.35* 7.65 0.82 7.88 10.08*

Sunstar 2.14* 10.07 0.51 8.11 10.12*

SWI-1014 2.15* 11.33 0.63 10.43 10.22*

GN-1 2.35* 7.24 0.58 4.72 10.58*

Riviera 2.04* 4.26 0.47 4.06 11.08*

Premier 2.39* 8.25 0.27 6.65 11.11*

Celebration 2.24* 7.45 0.89 6.14 11.23*

CIS-CD7 2.04* 5.81 0.49 3.89 11.35*

Patriot 2.25* 10.71 0.25 6.81 11.35*

Transcontinental 2.08* 7.08 0.48 6.89 11.56*

SWI-1045 2.51* 7.19 0.58 7.39 12.06*

Yukon 2.09* 7.21 0.43 6.53 7.86*

Southern Star 2.13* 8.20 0.45 5.01 8.75*

SWI-1012 2.14* 6.93 0.58 7.61 9.06*

La Paloma 2.11* 6.49 0.53 4.95 9.08*

Sunbird 2.08* 5.54 0.67 4.46 12.35

MS-Choice 2.28* 3.93 0.85 4.86 13.18

Tifsport 2.70* 9.81 0.64 8.01 13.19

Aussie Green 2.19* 6.79 0.43 8.52 15.09

SR 9554 1.88 6.09 0.50 4.19 10.46*

Arizona

Common 1.83 6.91 0.51 6.02 10.68*

CIS-CD6 2.01 7.76 0.41 6.92 11.14*

SWI-1001 2.02 7.51 0.62 6.61 11.34*

Mohawk 1.72 7.96 0.53 6.85 8.06*

53

Table 3.6. Shoot chlorophyll, clipping yield, root biomass, and thatch

accumulation of 42 field-grown bermudagrass cultivars at Clemson University in

July, 2006 and 2007 (continued).

Ashmore 1.99 7.52 0.65 7.23 8.21*

Sundevil 1.97 7.51 0.31 6.19 8.27*

B-14 1.73 6.33 0.63 5.62 8.49*

FMC-6 1.99 6.59 0.51 5.48 8.94*

NuMex Sahara 1.89 6.55 0.78 5.92 9.07*

Panama 1.88 5.90 0.49 4.05 9.86*

Princess 77 1.95 9.63 0.50 8.51 12.24

*Mean different from the statistically best cultivar using Dunnett‟s test ( = 0.05).

greatest root biomass in July, 2006 compared to other cultivars. In July 2007, TiftNo.2,

TiftNo.1, SWI-1046, Tifway, SWI-1044, SWI-1003, OKC 70-18, SWI-1014, and

Midlawn produced greatest root biomass compared to other cultivars. Meanwhile, CIS-

CD5 (3.84 g) and CIS-CD7 (3.89 g) produced least total root biomass in July, 2007.

Greatest thatch accumulation occurred for TiftNo.1 (12.23 g), SWI-1046 (13.88 g),

Tifway (14.42 g), TiftNo.4 (12.68 g), Sunbird (12.35 g), MS-Choice (13.18 g), Tifsport

(13.19 g), Aussie Green (15.09 g), and Princess 77 (12.24 g) compared to other cultivars.

Yukon produced the least amount of thatch (7.86 g). This cultivar is also known for its

relative cold tolerance (Anderson et al., 2002). In this study, no cultivation or

topdressing program was initiated during the study period; therefore, it should be noted

that thatch accumulation results could vary at a site where management practices, such as

aerification and topdressing routinely occurs.

Fall Performance

SWI-1046, Tifway, Midlawn, and Tifsport were the only cultivars to place in the

top statistical ratings for maintaining green color longer into the winter (Table 3.7).

54

Table 3.7. Percent fall dormancy of 42 bermudagrass cultivars rated

from 1 November to 15 December 2006 and 2007 at Clemson

University, Clemson, SC.

Percent Fall Dormancy† (0-100%)

Cultivar Wk 1 Wk 2 Wk 3 Wk 4 Wk 5

SWI-1046 23* 20* 30* 53* 75*

Tifway 15* 11* 18* 26* 60*

Midlawn 23* 8* 21* 36* 57*

Tifsport 3* 7* 16* 28* 61*

SWI-1045 35* 23* 40* 71 82

TiftNo.3 20* 28* 35* 61 87

TiftNo.4 26* 30* 41* 58 80

Riviera 50* 50* 57* 73 95

Yukon 42* 36* 50* 81 90

Ashmore 36* 36* 55* 70 97

OKC 70-18 38* 20* 28* 60 85

SWI-1012 55 43* 55* 81 92

SWI-1014 35* 50* 66 83 93

SWI-1041 33* 57 50* 63 90

Arizona

Common 38* 67 58* 72 96

Mohawk 56 46* 53* 73 95

CIS-CD5 60 48* 60* 73 100

CIS-CD7 43* 60 56* 71 95

SR 9554 53* 53* 60 68 98

TiftNo.1 46* 60 62* 86 90

TiftNo.2 40* 56 55* 81 95

Princess 77 52 61 63* 80 93

SWI-1001 52 50 56* 63 92

Sundevil 65 63 61* 70 96

Southern Star 56 60 53* 63 98

Transcontinental 60 77 75* 88 97

Panama 71 57 55* 78 98

GN-1 60 60 51* 73 92

Premier 53 63 65* 70 90

Sunstar 62 78 66 73 96

55

Table 3.7. Percent fall dormancy of 42 bermudagrass cultivars rated

from 1 November to 15 December 2006 and 2007 at Clemson

University, Clemson, SC (continued).

B-14 62 70 71 85 100

SWI-1003 58 60 65 75 93

SWI-1044 51 57 70 83 95

NuMex Sahara 60 70 66 78 100

FMC-6 70 80 78 81 100

MS-Choice 76 73 83 88 100

CIS-CD6 70 80 85 86 100

La Paloma 46 60 68 81 98

Aussie Green 80 86 88 86 98

Patriot 70 68 73 92 100

Celebration 57 70 70 92 93

Sunbird 78 85 88 88 100

*Mean different from the statistically best cultivar using Dunnett‟s test

( = 0.05). †Percent fall dormancy based on a scale of 0-100%, 0% = complete

green bermudagrass, 100% = complete brown bermudagrass.

Celebration, Aussie Green, and MS-Choice were among the quickest cultivars to break

dormancy in the spring (Table 3.1), however, these cultivars entered dormancy early in

the fall and winter (Illustration D.5). On the 4th

and 5th

rating date, SWI-1046, Tifway,

Midlawn, and Tifsport had less brown tissue present compared to other bermudagrass

cultivars. CIS-CD5, B-14, NuMex Sahara, FMC-6, MS-Choice, CIS-CD6, Sunbird, and

Patriot were the first cultivars to reach 100% brown. Meanwhile, Midlawn was the only

cultivar by the end of the study to have less than 60% dormancy. A potential concern for

cultivars that delay entering dormancy may incur increased freeze damage. However,

recent studies reveal that increasing N rates late in the growing season to retain green

color longer into winter does not increase bermudagrass winter-kill (Richardson, 2002;

56

Munshaw et al., 2006). Therefore, cultivars with late season color retention may be a

very desirable characteristic in the transition zone.

In the fall, no cultivar placed in the top statistical category for all parameters

measured (Table 3.8). However, SWI-1003, SWI-1044, SWI-1045, SWI-1001, TiftNo.4,

Tifway, and TiftNo.2 were in the top statistical category for five of the six parameters

collected. In September, only Mohawk, Patriot, B-14, Arizona Common, and Ashmore

were below TQ acceptable threshold. In October, no cultivars TQ was higher than 7,

however, Tifway (6.9) and TiftNo.4 (6.9) maintained highest TQ scores. Shoot

chlorophyll concentrations were similar among cultivars, however, SWI-1003, SWI-

1001, TiftNo.2, SWI-1046, Princess 77, NuMex Sahara, CIS-CD6, TiftNo.1, Southern

Star, and Ashmore had significantly less chlorophyll accumulation compared to other

bermudagrass cultivars. Cultivars with greatest root biomass (>0.5 g) in the fall were

SWI-1001, TiftNo.2, SWI-1046, TiftNo.3, Transcontinental, and TiftNo.1. Cultivars

with greatest thatch accumulation (>12 g) were TiftNo.4, TiftNo.3, Tifsport, MS-Choice,

Aussie Green, Celebration, Riviera, Premier, and TiftNo.1, while Mohawk, Panama,

Arizona Common produced least amount of thatch (<8 g).

Conclusion

The future for improved bermudagrasses coming to the market seems promising.

Many experimental cultivars produced from breeding programs around the country

showed excellent results. For example, the only cultivars that placed in the top statistical

57

Table 3.8. Turfgrass quality, clipping yield, shoot chlorophyll, total root biomass,

and thatch accumulation of 42 field-grown bermudagrass cultivars at Clemson

University in September, 2006 and 2007.

Turfgrass Quality†

Cultivar September October

Clipping

Yield

(g)

Shoot

Chlorophyll

(mg g-1

)

Root

Biomass

(g) Thatch

(g)

SWI-1003

7.3* 6.4* 4.31* 1.53 0.41* 11.52*

SWI-1044

7.2* 6.1* 5.97* 1.76* 0.42 11.59*

SWI-1045

7.2* 6.4* 2.66 1.75* 0.48* 11.42*

SWI-1001

7.0* 6.1* 3.46* 1.51 0.50* 10.27*

TiftNo.4

7.5* 6.9* 6.50* 1.61* 0.46* 12.62

Tifway

7.3* 6.9* 7.02* 1.76* 0.31 11.84*

TiftNo.2

7.0* 6.2* 5.69* 1.47 0.50* 11.70*

SWI-1014

6.6 5.8 7.31* 1.67* 0.38* 9.53*

SWI-1041

6.8 6.3* 6.11* 1.65* 0.35 8.31*

SWI-1046

6.8 6.4* 4.91* 1.52 0.52* 10.47*

Princess 77

6.9* 5.8 6.21* 1.37 0.38* 9.82*

TiftNo.3

6.5 6.3* 4.09* 1.72* 0.62* 12.21

Midlawn

6.6 6.1* 5.24* 2.08* 0.23 9.05*

Tifsport

7.2* 6.5* 3.98* 1.68* 0.29 14.56

MS-Choice

7.8* 6.2* 2.56 1.91* 0.41* 13.20

Transcontinental

6.9* 5.6 3.12 1.91* 0.52* 10.53*

Aussie Green

7.4* 6.0* 4.10* 1.70* 0.14 17.35

GN-1

7.1* 6.0* 1.97 1.64* 0.20 11.32*

Celebration

7.4* 6.5* 3.14 1.76* 0.42* 12.94

Sunstar

6.0 5.0 3.54* 1.85* 0.24 8.76*

SWI-1012

7.1* 5.7 2.31 1.86* 0.32 11.43*

NuMex Sahara

6.1 5.2 4.07* 1.44 0.38* 10.07*

Mohawk

5.9 5.3 2.68* 1.69* 0.29 6.47*

Riviera

6.9* 6.0* 2.82 1.73* 0.27 12.65

CIS-CD7

6.8 5.5 2.85* 1.62* 0.34 9.86*

Panama

6.5 5.0 3.48* 1.56* 0.24 7.48*

La Paloma

6.6 5.3 3.38* 1.73* 0.33 9.99*

SR 9554

6.5 5.0 3.68* 1.82* 0.22 10.21*

Yukon

6.8 5.7 7.56* 1.68* 0.22 8.23*

Premier

6.2 6.0* 4.30* 1.74* 0.16 12.30

Patriot

5.5 4.8 7.96* 1.59* 0.09 8.03*

B-14

5.9 5.2 2.99 1.76* 0.27 8.06*

Arizona

Common

5.6 5.0 2.79 1.68* 0.21 7.57*

FMC-6

6.4 5.3 3.31 1.73* 0.34 9.42*

Sundevil

6.0 4.9 2.93 1.84* 0.29 9.34*

58

Table 3.8. Turfgrass quality, clipping yield, shoot chlorophyll, total root biomass,

and thatch accumulation of 42 field-grown bermudagrass cultivars at Clemson

University in September, 2006 and 2007 (continued).

CIS-CD5

6.7 5.7 3.14 1.83* 0.32 9.27*

CIS-CD6

6.3 5.3 4.22* 1.45 0.28 9.64*

OKC 70-18

6.5 5.8 3.21 2.14* 0.27 10.53*

TiftNo.1

6.8 5.9 6.92* 1.28 0.50* 12.55

Sunbird

6.2 4.9 3.12 1.65* 0.32 9.89*

Southern Star

6.3 5.3 3.04 1.51 0.26 10.70*

Ashmore

5.8 5.5 2.92 1.47 0.16 9.84*

*Mean different from the statistically best cultivar using Dunnett‟s test ( = 0.05). †Turfgrass quality based on a scale of 1 – 9, 1 = brown/dead turfgrass, 7 = minimally

acceptable turfgrass, 9 = ideal green, healthy turfgrass.

category for all parameters measured in spring (OKC 70-18 and SWI-1046) and summer

(TiftNo.2) were experimental turfgrasses. In the fall, with the exception of Tifway, the

only cultivars that placed in the top five of the six parameters measured were

experimental cultivars. Also, few trends emerged during the study where one cultivar

could be recommended above all others. Cultivars performance varied depending on

time of year (i.e., spring, summer, or fall). At times, the same cultivar performed

significantly different from year to year. While Tifway continues to be the industry

standard, many new cultivars possess improved traits relative to Tifway. Therefore,

when a turfgrass manager is considering establishing/renovating a turfgrass site with

bermudagrass, considerations such as traffic, soil type, light intensity, temperature stress,

water availability, water quality, fertility programs, mowing practices, topdressing

regimes, and cultivation programs should all be taken into account when selecting

bermudagrass cultivars. Future studies should investigate the establishment rates, stress

59

tolerance of these cultivars (i.e., drought, salinity, aluminum), and timing of

establishment.

60

CHAPTER IV

DIVERSITY OF 42 BERMUDAGRASS CULTIVARS IN A REDUCED LIGHT

ENVIRONMENT

Introduction

Bermudagrass‟s (Cynodon spp.), a C4 plant, growth and development is

interrupted when light interception is reduced. In shade, warm-season turfgrass decline is

attributed to morphological limitations, such as reduced lateral stem growth (Beard,

1997). A shaded micro-environment initiates excessive shoot vertical growth, depleting

turfgrass root carbohydrate status (Qian and Engelke, 1999). Previous warm- and cool-

season turfgrass evaluations have noted an increase in vertical shoot growth as shade

increases (Qian et al., 1998; Tegg and Lane, 2004a).

Characteristics of C4 plants include high growth rates, low photorespiration rates,

high photosynthetic rates, and minimal water loss due to unique anatomical features

compared to C3 plant species. C4 anatomy allows plants to maintain high levels of CO2

near ribulose bisphosphate carboxylase/oxygenase (Rubisco) allowing water conservation

on hot days and a positive net carbon gain when environmental CO2 is low. However,

this unique anatomical organization may reduce C4 plant species ability to adapt to

variable environments, such as low light, because C4 photosynthesis requires coordinated

changes between mesophyll and bundle sheath tissues, whereas C3 photosynthetic tissues

require minimal coordination (Sage and McKown, 2006). Specifically, C4 plants can not

readily adapt to sunflecks that typically occur in heavily shaded environments due to

61

distance between mesophyll CO2 fixation reactions and bundle sheath Calvin cycle

metabolites (Horton and Neufeld, 1998).

Bermudagrasses continue to be the preferred turfgrass species used in the

southern United States (McCarty and Miller, 2002; McCarty, 2005), however, its use is

often limited when optimal light interception is interrupted. For example, a „TifEagle‟

bermudagrass putting green requires 32.6 mol m-2

d-1

for acceptable (≥7) turfgrass quality

(TQ) (Bunnell et al., 2005a), while „Floradwarf‟ and „Tifdwarf‟ bermudagrass requires

38.6 mol m-2

d-1

for sustained growth (Miller et al., 2005). Cultural practices to enhance

warm-season turfgrass TQ under shade includes raising mowing heights (Bunnell et al.,

2005b; White, 2004), reducing nitrogen (N) rates (Bunnell et al., 2005b; Goss et al.,

2002; Bell and Danneberger, 1999b; Burton et al., 1959), applying plant growth

regulators (Bunnell et al., 2005b; Ervin et al., 2002; Qian et al., 1998; Qian and Engelke,

1999), and watering deeply and infrequently (Dudeck and Peacock, 1992).

Variation among C4 turfgrasses shade sensitivity has been previously investigated.

Bunnell et al. (2005c) reported „Meyer‟ Japanese zoysiagrass (Zoysia japonica Steud.)

had greatest shade tolerance maintaining acceptable TQ (>7) at 71%, „Celebration‟

bermudagrass at 58%, and „TifSport‟ and „Tifway‟ bermudagrass at 41% continuous

shade. Jiang et al. (2004) noted significant variation between seashore paspalum

(Paspalum vaginatum Swartz) and bermudagrass entries under 70% and 90% shade.

„Sea Isle 1‟ and „Temple 1‟ paspalum were shade tolerant, while TifSport and TifEagle

bermudagrass showed least shade tolerance. In a similar study, Jiang et al. (2005) also

noted greater shade tolerance of Sea Isle 1 compared to TifSport bermudagrass.

62

Gaussoin et al. (1988) noted the diversity of 32 bermudagrass cultivars under 90%

uninterrupted shade. According to results, „Boise‟, „No Mow‟, and „NM 2-13‟ were

relatively shade tolerant, while „Arizona Common‟ and „Santa Ana‟ were relatively shade

sensitive. Due to the genetic variation and diversity among existing bermudagrass

cultivars, it is critical to continue shade tolerance evaluation of new bermudagrass

cultivars. Therefore, the objectives of this research were to evaluate bermudagrass

growth and determine the diversity of 42 bermudagrass cultivars maintained at 64%

reduced irradiance.


This two-year greenhouse study was conducted from 15 June 2005 to 15 August

2005 and repeated in 2006 at Clemson University (Clemson, SC) (Illustration D.6).

Greenhouse conditions averaged 30.8oC /26.2

oC high/low air temperature and 73%

relative humidity for both years. Environmental conditions (temperature and humidity)

were maintained by an automated computer recording system (Argus Controls,

Whiterock, British Columbia V4B 3Y9).

This study consisted of two light treatments: a control (full-sunlight) and 64%

continuous shade applied daily using a neutral density, polyfiber black shade cloth

(Glenn Harp and Sons, Inc., Tucker, GA). The reduced light treatment was chosen to

identify relatively shade-tolerant bermudagrass cultivars. Shade clothes were placed on a

polyvinyl chloride (PVC) structure 15.2 cm in length and 12.7 cm in diameter with 2.5

cm diameter PVC pipes. Shade tents were 30.48 cm above the turf surface to reduce

63

early morning and late afternoon sunlight encroachment. Photon flux density ( mol m-2

s-1

) and light quality were measured on a clear, cloudless day using a quantum radiometer

(Model LI-250, LiCor, Lincoln, NE) and spectroradiameter (Model LI-1800; LiCor, Inc.,

Lincoln, NE). Surface temperatures for both treatments were recorded twice on a

clear/cloudless day using an indoor/outdoor thermometer (model# 1455, Taylor,

Oakbrook, IL).

Plugs were collected from the 2002 bermudagrass National Turfgrass Evaluation

Program (NTEP) (Table A.1) field research plots located at Clemson University and

transplanted into cone-tainers with 85% sand and 15% peat as growth media. Cone-

tainer dimensions were 25.4 cm in height and 5.1 cm in diameter. Following potting,

plugs were allowed to establish for one month prior to treatment initiation. Fertilizers

were provided at 49 kg N ha-1

every two weeks using a complete fertilizer (16N-1.7P-

6.6K) with a slow release urea and micronutrients (kg•ha-1

): Calcium, 6; Magnesium, 3;

Sulfur, 9; Boron, 0.06; Copper, 0.03; Iron, 0.3; Manganese, 0.15; Molybdenum, 0.0015;

and Zinc, 0.15. Cone-tainers were mowed at a height of 12.8 mm four times a week with

clipping removal.

Data collection was identical in year I and II. Turfgrass quality ratings were

recorded weekly based on color, density, texture, and uniformity of the bermudagrass

surface. Quality was visually evaluated from 1 to 9, 1 = brown, dead turf, 6 = minimal

acceptable turf, 9 = ideal green, healthy turf.

Root biomass (g) and length (cm) were determined at the end of the study. Roots

were extracted from the soil and thoroughly washed until all soil was removed.

64

Following soil removal, root length was measured from the base of the thatch to the

longest fully extended root present. Roots were then clipped from the base of thatch and

dried in an oven at 80.0 oC for 48 hours. Once dried, samples were weighed to determine

total root biomass.

Chlorophyll (mg g-1

) was recorded at week 4 and 8. Clippings were collected

from each cone-tainer and immediately placed in a plastic bag inside a covered bucket to

prevent sunlight degradation. Clippings were weighed (0.1g) and placed in a glass test

tube (1.0 cm in width and 14.8 cm in length) with 10 ml of dimethyl sulfoxide (DMSO)

(Hiscox and Israelstam, 1979). Samples were incubated in 65 oC water on a hot plate

(PC-600, Corning, Corning, NY) for 1.5 hours and continuously shaken. Upon

completion, samples were passed through filter paper (Whatman 41, Whatman, England)

and remaining extract (2 ml) was transferred into cuvettes. The absorbance values were

recorded at 663 nm and 645 nm wavelengths using a Spectrophotometer (GenesysTM

20,

ThermoSpectronic, Rochester, NY). The following formula was used to calculate total

chlorophyll = (8.02 * D663 + 20.2 * D645) * 0.1 (Arnon, 1949).

Data Analysis

Each treatment was replicated three times in a randomized complete block design.

Data from both years were combined as treatment by year interactions were not

significant. All statistical computations were conducted using analysis of variance

(ANOVA) within the Statistical Analysis System (SAS Institute, 2005) with means

separated by Fisher‟s Least Significance Difference (LSD) test. An alpha of 0.05 was

used to determine statistical significance.

65

Results

Micro-environment

Compared to full-sunlight, shade cloths reduced temperatures 13%, while no

difference in light quality were detected. Although light quality has been shown to

impact turfgrass growth (Wherley et. al., 2005), the focus of this study was stadium

(artificial) shade. The greenhouse glass provided an additional 9% reduction in solar

irradiance for all treatments.

Turfgrass quality

Most cultivars visual TQ scores dropped well below acceptable threshold of 6

following 4 weeks of 64% continuous shade (Table 4.1). Poorest performing cultivars

included NuMex Sahara (3.8), Arizona Common (4.2), B-14 (4.3), and Panama (4.3),

while Aussie Green (7.2), Celebration (6.5), TiftNo.4 (6.2), TiftNo.1 (6.3), Sunbird (6.2),

and Transcontinental (6.0) maintained acceptable TQ ratings following 4 weeks of 64%

shade (Illustration D.7). Industry standards, Tifway and TifSport, had TQ scores of 5.0

and 5.5, respectively. After 8 weeks of continuous 64% shade, all cultivars had severe

tissue discoloration. However, Aussie Green (5.3), TiftNo.4 (4.8), and Celebration (4.5)

maintained significantly higher TQ scores compared to Patriot (2.5), Premier (2.7),

NuMex Sahara (2.7), Panama (2.7), La Paloma (2.8), and Midlawn (2.8). In the absence

of shade, most cultivars maintained or showed near acceptable TQ by week 8.

Within week 4 TQ ratings, shade grown cultivars Transcontinental, CIS-CD6,

Aussie Green, Celebration, TiftNo.1, TiftNo.2, TiftNo.4, and Mohawk did not have

66

Table 4.1. Turfgrass quality of 42 bermudagrass cultivars after 4 and 8 weeks of full-

sunlight (control) and 64% continuous shade at the Clemson University greenhouse

research complex.

Week 4 Week 8

Cultivar Full-

Sun Shade Full-Sun Shade Rank

†

Celebration 7.5a-c‡ 6.5ab 7.3a-d A 4.5a-c B 2/2

TiftNo.4 7.3a-d 6.2a-d 7.8a A 4.8ab B 2/2

TiftNo.1 7.2b-e 6.3a-c 7.2a-d A 4.3a-d B 2/2

Transcontinental 7.0c-f 6.0a-e 6.8b-f A 4.3a-d B 2/2

SWI-1003 8.0a A§ 5.7b-f B 7.3a-d A 3.5c-i B 0/2

Sunbird 7.5a-c A 6.2a-d B 7.3a-d A 4.3a-d B 2/2

Aussie Green 7.5a-c 7.2a 7.8a A 5.3a B 2/2

MS-Choice 6.8c-g A 5.8b-e B 7.3a-d A 3.7c-h B 0/2

Princess 77 7.2b-e A 5.3b-h B 6.8b-f A 3.7c-h B 0/2

SWI-1045 7.2b-e A 5.5b-g B 7.0a-e A 3.7c-h B 0/2

SWI-1041 7.8ab A 5.3b-h B 7.3a-d A 3.5c-i B 0/2

SWI-1012 7.0c-f A 5.3b-h B 7.0a-e A 4.0b-f B 0/2

B-14 6.3f-i A 4.3g-i B 6.0fg A 3.0f-i B 0/2

Riviera 7.2b-e A 5.7b-f B 7.7ab A 3.7c-h B 0/2

SWI-1046 7.2b-e A 5.3b-h B 6.7c-f A 4.0b-f B 0/2

TiftNo.3 6.7d-h A 4.8e-i B 6.5d-f A 4.0b-f B 0/2

Southern Star 7.0c-f A 5.3b-h B 6.8b-f A 3.7c-h B 0/2

TiftNo.2 6.8c-g 5.5b-g 7.0a-e A 4.2b-e B 0/2

Sunstar 6.3f-i A 4.5f-i B 6.2e-g A 3.2e-i B 0/2

SWI-1044 6.8c-g A 5.3b-h B 7.5a-c A 4.0b-f B 0/2

FMC-6 6.5e-i A 5.0d-i B 6.7c-f A 3.5c-i B 0/2

Mohawk 6.7d-h A 5.3b-h B 6.2e-g A 3.2e-i B 0/2

SWI-1001 6.8c-g A 4.8e-i B 7.0a-e 3.8b-g B 0/2

Tifway 7.5a-c A 5.0d-i B 7.5a-c A 3.2e-i B 0/2

Midlawn 6.5e-i A 4.8e-i B 6.5d-f A 2.8g-i B 0/2

Tifsport 7.2b-e A 5.5b-g B 7.7ab A 3.3d-i B 0/2

Premier 6.7d-h A 5.2c-h B 7.3a-d A 2.7hi B 0/2

Ashmore 6.8c-g A 4.8e-i B 6.7c-f A 3.2e-i B 0/2

CIS-CD5 6.2g-j A 5.0d-i B 6.8b-f A 3.3d-i B 0/2

CIS-CD6 6.3f-i 5.2c-h 7.0a-e A 3.3d-i B 0/2

CIS-CD7 6.7d-h A 5.3b-h B 6.8b-f A 3.2e-i B 0/2

Panama 6.2g-j A 4.3g-i B 7.2a-d A 2.7hi B 0/2

La Paloma 6.0h-j A 4.5f-i B 6.7c-f A 2.8g-i B 0/2

Yukon 7.0c-f A 5.5b-g B 7.3a-d A 3.2e-i B 0/2

OKC 70-18 7.0c-f A 4.8e-i B 7.0a-e A 3.2e-i B 0/2

NuMex Sahara 5.8ij A 3.8i B 6.0fg A 2.7hi B 0/2

SWI-1014 7.5a-c A 5.5b-g B 7.2a-d A 3.2e-i B 0/2

GN-1 6.2g-j A 4.5f-i B 6.2e-g A 3.2e-i B 0/2

Patriot 6.3f-i A 4.5f-i B 6.5d-f A 2.5i B 0/2

Sundevil 6.7d-h A 5.0d-i B 6.8b-f A 3.7c-h B 0/2

SR 9554 6.3f-i A 4.8e-i B 6.7c-f A 3.0f-i B 0/2

67

Table 4.1. Turfgrass quality of 42 bermudagrass cultivars after 4 and 8 weeks of full-

sunlight (control) and 64% continuous shade at the Clemson University greenhouse

research complex (continued).

Arizona

Common 5.5j A 4.2hi B 5.5g A 3.0f-i B 0/2

†Rank indicates number of times a cultivar placed in the top statistical category when grown

under 64% shade. Greatest shade tolerance = 2/2, greatest shade sensitivity = 0/2. ‡Values within a column followed by the same letter are not significantly different at P≤0.05 by

protected LSD. §Values within a row within in each week followed by the same letter are not significantly

different at P≤0.05 by protected LSD. Turfgrass quality based on a scale of 1 – 9, 1 = brown/dead turfgrass, 6 = minimal acceptable

turfgrass, 9 = ideal green, healthy turfgrass.

significant TQ reductions compared to full-sunlight. However, within week 8, all

cultivars grown in shade had a significant TQ decline compared to full-sunlight ratings.

Chlorophyll

Significant differences occurred for shoot chlorophyll concentrations at weeks 4

and 8 (Table 4.2). The shade-grown cultivar with highest chlorophyll was TiftNo.4 at

week 4 (2.47) and week 8 (2.77), while TifSport and Arizona Common had lowest

chlorophyll concentrations at week 4 (1.54) and week 8 (1.31), respectively. SWI-1003,

SWI-1041, Princess 77, and TiftNo.1 had ~33% greater chlorophyll than Tifway,

Southern Star, GN-1, and Arizona Common at this time. By week 8, SWI-1003, SWI-

1012, SWI-1045, SWI-1046, SWI-1041, and Celebration had ~45% greater chlorophyll

when grown in shade than GN-1, SWI-1014, NuMex Sahara, OKC 70-18, B-14, and

Ashmore.

SWI-1041, TiftNo.1, and Yukon produced significantly higher chlorophyll

concentrations at week 4 when grown in shade compared to full-sunlight, however, this

response was transient (Table 4.2). Transient increases in chlorophyll content have

68

Table 4.2. Total shoot chlorophyll (mg g-1

) concentration of 42 bermudagrass cultivars after

4 and 8 weeks of full-sunlight (control) and 64% continuous shade at the Clemson

University research greenhouse complex.

Week 4 Week 8

Cultivar Full Sun Shade Full Sun Shade Rank†

Celebration 1.78b-h‡ 2.08a-e 2.64 2.24a-e 2/2

TiftNo.4 2.39a 2.47a 3.19 2.77a 2/2

TiftNo.1 1.70b-h

B§

2.15a-e

A 2.71 2.13b-f 1/2

Transcontinental 1.72b-h 1.95a-h 2.53 1.82c-j 1/2

SWI-1003 2.00b 2.30ab 2.97 2.31a-d 2/2

Sunbird 1.57d-h 1.90b-h 2.43 2.15b-f 0/2

Aussie Green 1.74b-h 1.92b-h 2.42 A 1.87c-j B 0/2

MS-Choice 1.89b-d 2.07a-e 2.24 1.75e-j 1/2

Princess 77 1.67b-h 2.22a-d 2.54 2.09b-h 1/2

SWI-1045 1.76b-h 2.10a-e 2.34 2.36a-c 2/2

SWI-1041 1.84b-f

B

2.29a-c

A 2.97 2.24a-e 2/2

SWI-1012 1.88b-d 1.95b-h 2.78 2.60ab 1/2

B-14 1.46gh 1.83d-h 2.45 A 1.69e-j B 0/2

Riviera 1.71b-h 1.91b-h 2.64 1.98c-i 0/2

SWI-1046 1.96bc 2.06b-e 2.75 A 2.22b-e B 0/2

TiftNo.3 1.48f-h 1.90b-h 2.13 2.13b-f 0/2

Southern Star 1.45gh 1.78e-h 2.18 2.11b-h 0/2

TiftNo.2 1.71b-h 1.93b-h 2.82 2.12b-g 0/2

Sunstar 1.42h 1.79e-h 2.19 1.88c-j 0/2

SWI-1044 1.93b-d 2.04b-f 2.58 2.03c-h 0/2

FMC-6 1.65b-h 1.85d-h 2.22 1.92c-j 0/2

Mohawk 1.50e-h 1.78e-h 2.18 2.06b-h 0/2

SWI-1001 1.89b-d 1.93b-h 2.33 1.90c-j 0/2

Tifway 1.84b-f 1.60gh 2.61 1.84c-j 0/2

Midlawn 1.83b-g 1.93b-h 2.57 A 1.95c-j B 0/2

Tifsport 1.81b-g 1.54h 2.56 1.98c-i 0/2

Premier 2.01b 1.93b-h 2.84 A 1.74e-j B 0/2

Ashmore 1.87b-e 1.85d-h 2.62 A 1.47ij B 0/2

CIS-CD5 1.78b-h 1.89b-h 2.55 A 1.82c-j B 0/2

CIS-CD6 1.56d-h 1.81d-h 2.24 1.71e-j 0/2

CIS-CD7 1.60c-h 1.87d-h 2.32 1.80d-j 0/2

Panama 1.80b-h 1.86d-h 2.52 A 1.77d-j B 0/2

La Paloma 1.67b-h 1.85d-h 2.14 A 1.68f-j B 0/2

Yukon 1.58d-h

B

1.88c-h

A 2.48 A 1.85c-j B 0/2

OKC 70-18 1.97bc 1.95-f 2.7 A 1.67f-j B 0/2

NuMex Sahara 1.85b-f 1.98b-g 2.52 A 1.56h-j B 0/2

69


) concentration of 42 bermudagrass cultivars after

4 and 8 weeks of full-sunlight (control) and 64% continuous shade at the Clemson

University research greenhouse complex (continued).

SWI-1014 1.74b-h 1.85d-h 2.78 A 1.58g-j B 0/2

GN-1 1.88b-d 1.74e-h 2.48 A 1.67f-j B 0/2

Patriot 1.82b-g 1.86d-h 2.55 A 1.73e-j B 0/2

Sundevil 1.61c-h 1.88c-h 2.36 2.19b-f 0/2

SR 9554 1.69b-h 1.91b-h 2.38 1.78d-j 0/2

Arizona Common 1.62c-h 1.63f-h 2.09 1.43j 0/2 †Rank indicates number of times a cultivar placed in the top statistical category when grown under

64% shade. Greatest shade tolerance = 2/2, greatest shade sensitivity = 0/2. ‡Values within a column followed by the same letter are not significantly different at P≤0.05 by protected

LSD.

§Values within a row within each week followed by the same letter are not significantly different at P≤0.05 by

protected LSD.

previously been reported under other environmental stresses (Jiang and Huang, 2001).

Within week 8, many cultivars chlorophyll concentration declined. Compared to

full-sunlight, shade-grown cultivars Ashmore, SWI-1014, B-14, and Premier, had a

~66% decline in chlorophyll, while SWI-1046, La Paloma, Aussie Green, and Midlawn

showed a ~28% chlorophyll reduction.

Root Length

Overall, root length was least affected by shade compared to other parameters

measured. No significant differences were noted for root length when grown in full-

sunlight (Table 4.3). Cultivars grown under 64% shade exhibited some statistically

different root lengths. Most striking differences were TiftNo.2 producing 89% greater

root length than Arizona Common, while SWI-1014 had a 57% root length reduction

compared to Riviera. Shade-grown Arizona Common, SWI-1014, and Sundevil, had

63%, 59%, and 41% decreases, respectively, compared their sun-grown counterparts.

70

Table 4.3. Root length (cm) of 42 bermudagrass cultivars after 8

weeks of full-sunlight (control) and 64% continuous shade at the

Clemson University research greenhouse complex.

Cultivar Sun Shade Rank†

Celebration 8.78 7.00a-d‡ 1/1

TiftNo.4 9.23 8.72a-d 1/1

TiftNo.1 9.20 8.27a-e 1/1

Transcontinental 9.62 A§ 8.40a-e B 1/1

SWI-1003 8.87 8.97ab 1/1

Sunbird 9.43 8.30a-e 1/1

Aussie Green 9.35 8.91ab 1/1

MS-Choice 8.76 8.70a-d 1/1

Princess 77 9.78 8.08a-e 1/1

SWI-1045 9.47 8.18a-e 1/1

SWI-1041 9.93 A 8.52a-e B 1/1

SWI-1012 9.13 8.37a-e 1/1

B-14 9.45 8.90a-c 1/1

Riviera 9.52 9.03ab 1/1

SWI-1046 9.58 A 8.00a-e B 1/1

TiftNo.3 9.32 8.52a-e 1/1

Southern Star 9.53 9.25ab 1/1

TiftNo.2 9.43 9.60a 1/1

Sunstar 8.85 6.67c-g 0/1

SWI-1044 9.45 8.80a-c 1/1

FMC-6 9.10 7.60a-f 1/1

Mohawk 9.42 A 7.74a-f B 1/1

SWI-1001 9.08 8.42a-e 1/1

Tifway 9.45 8.63a-d 1/1

Midlawn 9.22 7.63a-f 1/1

Tifsport 10.23 A 8.87a-c B 1/1

Premier 8.70 8.78a-d 1/1

Ashmore 9.92 7.85a-f 1/1

CIS-CD5 10.13 A 8.28a-e B 1/1

CIS-CD6 9.45 8.33a-e 1/1

La Paloma 8.83 7.45a-f 1/1

Yukon 8.80 7.73a-f 1/1

OKC 70-18 8.30 8.75a-d 1/1

NuMex Sahara 9.32 7.50a-f 1/1

SWI-1014 9.15 A 5.75fg B 0/1

GN-1 8.97 7.05b-g 0/1

Patriot 8.39 6.37e-g 0/1

Sundevil 9.23 A 6.55d-g B 0/1

71

Table 4.3. Root length (cm) of 42 bermudagrass cultivars after 8

weeks of full-sunlight (control) and 64% continuous shade at the

Clemson University research greenhouse complex (continued).

SR 9554 8.5 A 6.28e-g B 0/1

Arizona Common 8.3 A 5.08g B 0/1 †Rank indicates number of times a cultivar placed in the top statistical

category when grown under 64% shade. Greatest shade tolerance = 1/1,

greatest shade sensitivity = 0/1. ‡Values within a column followed by the same letter are not

significantly different at P≤0.05 by protected LSD. §Values within a row followed by the same letter are not significantly

different at P≤0.05 by protected LSD.

Root Biomass

Each cultivar, regardless of shade tolerance or sensitivity, had a significant

reduction in root biomass (Table 4.4). Under shade, cultivars with least root mass

reduction (~121%) included B-14, NuMex Sahara, TiftNo.3, and MS-Choice, while

cultivars with greatest root mass decline (~325%) included SWI-1001, SR9554, and

Yukon, compared to full-sun. In addition, shade-grown SR9554 had a 265% decrease in

root biomass compared to SWI-1003. Celebration and TiftNo.2 also produced ~124%

greater root biomass when grown in shade compared to Arizona Common and GN-1

(Illustration D8).

Discussion

These results suggest great potential for future breeding programs the focus on

shade-tolerance improvement of bermudagrass. Bermudagrass cultivars, especially

newer ones, demonstrated great diversity. Based on rank for TQ, chlorophyll, root

72

Table 4.4. Total root biomass (g) of 42 bermudagrass cultivars after 8

weeks of full-sunlight (control) and 64% continuous shade at the Clemson


Cultivar Full Sun Shade Rank†

Celebration 0.201ab‡ A

§ 0.064a-e B 1/1

TiftNo.4 0.127d-l A 0.049b-m B 0/1

TiftNo.1 0.207a A 0.053a-k B 1/1

Transcontinental 0.179a-d A 0.067a-c B 1/1

SWI-1003 0.175a-e A 0.073a B 1/1

Sunbird 0.178a-d A 0.056a-j B 1/1

Aussie Green 0.095i-m A 0.038f-o B 0/1

MS-Choice 0.161a-h A 0.069ab B 1/1

Princess 77 0.173a-f A 0.059a-h B 1/1

SWI-1045 0.146b-j A 0.044c-m B 0/1

SWI-1041 0.149b-i A 0.048b-m B 0/1

SWI-1012 0.163a-h A 0.056a-j B 1/1

B-14 0.116f-m A 0.051a-l B 1/1

Riviera 0.189a-c A 0.061a-f B 1/1

SWI-1046 0.147b-j A 0.052a-l B 1/1

TiftNo.3 0.127d-l A 0.060a-g B 1/1

Southern Star 0.187a-c A 0.058a-i B 1/1

TiftNo.2 0.155a-h A 0.066a-d B 1/1

Sunstar 0.170a-g A 0.052a-l B 1/1

SWI-1044 0.126d-l A 0.045b-n B 0/1

FMC-6 0.113g-m A 0.050b-m B 0/1

Mohawk 0.124d-m A 0.041e-o B 0/1

SWI-1001 0.162a-h A 0.037g-o B 0/1

Tifway 0.118e-m A 0.041e-o B 0/1

Midlawn 0.067m A 0.025no B 0/1

Tifsport 0.146b-j A 0.042e-o B 0/1

Premier 0.091j-m A 0.032k-o B 0/1

Ashmore 0.163a-h A 0.041e-o B 0/1

CIS-CD5 0.133c-k A 0.033j-o B 0/1

CIS-CD6 0.095i-m A 0.036h-o B 0/1

Yukon 0.147b-j A 0.034j-o b 0/1

OKC 70-18 0.088k-m A 0.027m-o B 0/1

NuMex Sahara 0.085k-m A 0.040f-o B 0/1

SWI-1014 0.164a-h A 0.038g-o B 0/1

GN-1 0.108h-m A 0.029l-o B 0/1

Patriot 0.076lm A 0.030k-o B 0/1

Sundevil 0.110h-m A 0.043d-o B 0/1

73

Table 4.4 Total root biomass (g) of 42 bermudagrass cultivars after 8 weeks

of full-sunlight (control) and 64% continuous shade at the Clemson

University research greenhouse complex (continued).

SR 9554 0.081k-m A 0.020o B 0/1

Arizona Common 0.085k-m A 0.029l-o B 0/1 †Rank indicates number of times a cultivar placed in the top statistical category

when grown under 64% shade. Greatest shade tolerance = 1/1, greatest shade

sensitivity = 0/1. ‡Values within a column followed by the same letter are not significantly

different at P≤0.05 by protected LSD. §Values within a row followed by the same letter are not significantly different

at P≤0.05 by protected LSD.

biomass, and root length in 64% shade, the best cultivars were Celebration, TiftNo.4,

TiftNo.1, and Transcontinental (Table 4.5). Cultivars with intermediate shade tolerance

included Aussie Green, MS-Choice, Princess 77, SWI-1045, SWI-1041, and SWI-1012.

Most shade sensitive cultivars were SWI-1014, Arizona Common, Sundevil, SR 9554,

GN-1, and Patriot.

The top ranked cultivar across all parameters was Celebration (Table 4.5). When

grown in shade, Celebration was able to consistently maintain TQ, chlorophyll, root

length, and root biomass in the top statistical category. In a previous investigation,

Celebration was noted for its relative shade-tolerance (Bunnell et al., 2005c). At 71%

shade, Celebration and „Meyer‟ zoysiagrass maintained similar TQ scores at a 25 mm

mowing height, while Tifway and TifSport were deemed commercially unacceptable. In

this study, Celebration had TQ scores of 6.5 and 4.5 at weeks 4 and 8, respectively, while

Tifway and TifSport TQ scores were consistently lower throughout the duration of the

74

Table 4.5. Overall shade tolerance rank of 42 bermudagrass cultivars after 8

weeks of full-sunlight (control) and 64% continuous shade at the Clemson


Cultivar Rank† Cultivar Rank

Celebration 6 Mohawk 1

TiftNo.4 5 SWI-1001 1

TiftNo.1 5 Tifway 1

Transcontinental 5 Midlawn 1

SWI-1003 4 Tifsport 1

Sunbird 4 OR 2002 1

Aussie Green 3 Ashmore 1

MS-Choice 3 CIS-CD5 1

Princess 77 3 CIS-CD6 1

SWI-1045 3 CIS-CD7 1

SWI-1041 3 Panama 1

SWI-1012 3 La Paloma 1

B-14 2 Yukon 1

Riviera 2 OKC 70-18 1

SWI-1046 2 NuMex Sahara 1

TiftNo.3 2 SWI-1014 0

Southern Star 2 GN-1 0

TiftNo.2 2 Patriot 0

Sunstar 1 Sundevil 0

SWI-1044 1 SR 9554 0

FMC-6 1 Arizona Common 0

†Rank indicates number of times a cultivar placed in the top statistical category

when grown under 64% continuous shade. Greatest shade tolerance = 6, greatest

shade sensitivity = 0.

8-week study (Table 4.1). Jiang et al. (2004 and 2005) also noted TifSport bermudagrass

as shade-sensitive when compared to various seashore paspalum cultivars. Gaussoin et

al. (1988) noted Tifway as shade sensitive when compared to 31 other bermudagrass

cultivars.

75

Arizona Common was in the lowest statistical category for all parameters

measured when grown in shade. In another greenhouse shade study, Gaussoin et al.

(1988) regarded Arizona Common as highly shade-intolerant. Similar results in this

study were noted as Arizona Common did not rank in the top statistical category for any

of the measured parameters, indicating relative shade sensitivity.

Conclusion

While relative shade-tolerance of bermudagrass cultivars was examined in this

study, all cultivars had unacceptable TQ scores. Future research should examine the

relatively shade-tolerant and shade-intolerant cultivars to provide insight into the

physiological mechanisms associated with variation in shade response among

bermudagrass cultivars.

76

CHAPTER V

DORMANT BERMUDAGRASS SPRING GREEN-UP INFLUENCED BY SHADE

Introduction

Bermudagrass (Cynodon spp.) is the predominant turfgrass in warm climatic

regions of the world. However, when temperatures drop below 10oC, bermudagrass

becomes dormant. Due to this, managing bermudagrass in the transition zone is

challenging because of the relatively short growing season of bermudagrass. One major

challenge facing turfgrass managers is bermudagrass spring transition in the transition

zone. The potential of experimental and commercially available bermudagrass cultivars

ability to break dormancy earlier in the spring would greatly benefit many turfgrass

managers. Bermudagrass cultivars with earlier spring green-up (SGU) would benefit the

industry by providing use of sports fields and/or golf courses earlier in the year for

competition, earlier harvest times for sod producers, and perhaps eliminating overseeding

at certain sites.

Another limiting factor for bermudagrass growth and development occurs when

shade persists. Bermudagrass shade intolerance results from its inability to withstand low

light conditions because of its unique photosynthetic pathway (Sage and McKown, 2006;

Horton and Neufeld, 1998) and origin from hot, dry, and sub-humid regions of Africa

(McCarty et al., 2005). Typical responses of bermudagrass grown under shade include a

decrease in density (Jiang et al. 2004; Bunnell et al., 2005a, b; Miller et al., 2005), a

reduction in chlorophyll (Jiang et al. 2004; Bunnell et al., 2005a, b; Baldwin et al., 2008),

77

root mass (Baldwin et al., 2008) and carbohydrate production (Bunnell et al., 2005a, b,

c), decreased canopy photosynthetic rates (Jiang et al. 2004) and reduced antioxidant

enzyme activity (Jiang et al., 2005) and total soluble protein (Jiang et al., 2005)

production.

There have been several recent published reports attempting to either prolong

bermudagrass fall color or encourage bermudagrass breaking dormancy earlier through

the use of cultural practices, such as appropriate fertility (Richardson, 2002; Gilbert and

Kopec, 2004; Bruneau et al., 2004; Munshaw et al., 2006), plant growth regulator

(Fagerness and Yelverton, 2000 and Fagerness et al., 2002 and), colorant (Gilbert and

Kopec, 2004; Long et al., 2005; Liu et al., 2007), and temporary cover (Goatley et al.,

2005 and Goatley et al., 2007) use. To date, no study has evaluated bermudagrass

cultivars transition from winter dormancy into spring when shade is a growth limiting

factor. Also, several experimental and new commercially available bermudagrass

cultivars show improved shade tolerance compared to industry standards (Baldwin et al.,

2008; Hanna and Maw, 2007; Bunnell et al., 2005c). This study will aid turfgrass

managers in cultivar selection when establishing/renovating a tee-box or fairway when

shading is prevalent. Also, this project will benefit sod producers by identifying

bermudagrass cultivars ability to break dormancy earlier in the spring season allowing for

earlier harvest times. Finally, this research project will address how a shaded

microenvironment impacts bermudagrass cultivar SGU. Therefore, a research objective

was to evaluate bermudagrass cultivars SGU when shade is a growth limiting factor and

monitor bermudagrass summer performance following late winter and spring shade.

78


Research was conducted at the Turfgrass Research Center, Clemson University,

Clemson, SC from 2 March to 31 July 2006 and repeated in 2007. Bermudagrass

cultivars, „Tifway‟, „Tift No.4‟, „Celebration‟, „Princess 77‟, „Riviera‟, and „Yukon‟

(Table A.1), were maintained in lysimeters 40.64 cm in height and 15.24 cm in diameter

filled with 40.64 cm of 85:15 sand:peat and 10.16 cm gravel (8 to 10 mm in diameter) to

facilitate drainage. Plugs of dormant bermudagrass sod were collected from the 2002

bermudagrass NTEP trials at the Clemson University Research Center and washed free of

soil with roots clipped directly below the thatch layer. Lysimeters were maintained

adjacent to field research plots to mimic natural climatic field conditions (Illustration

D.9). Treatments included a control (full-sunlight) and 55% continuous shade using a

neutral density, polyfiber black shade cloth (Glenn Harp and Sons, Inc., Tucker, GA)

initiating light to moderate shade stress. Shade structures were metal frames with

individual cells measuring 304.8 cm in width, height, and length. Shade cloths supported

by metal frames were placed on top of the structure and extended 182.9 cm down each

side to prevent any morning or evening sunlight encroachment, yet also maintain

adequate air movement. Lysimeters were 81 cm above the ground and ~127 cm away

from each side of the shade material. Also, lysimeters were 227 cm below the top of the

shading material.

Weekly fertilization began 24 April 2006 and 10 April 2007 and ended 31 July

2006 and 2007 using a combination of 10N-1.3P-4.2K and 5N-0P-5.8K liquid fertilizers

79

(Progressive Turf, LLC., Ball Ground, GA) providing nitrogen at a rate of 9.7 kg ha-1

.

For overseeded treatments, fertilization was initiated 1-week following potting. Rates

and methods are similar as described above. A CO2-pressurized backpack sprayer was

used to apply all fertilizers. No fungicides and herbicides were applied as disease and

weed pressure were minimal. Lysimeters were watered daily (if necessary) to prevent

wilt, while mowing occurred every other day at 1.3 cm using a 7.2 volt cordless shear

(model #ssc1000, Black and Decker, Towson, MD).

Data collection

Data collection included visual SGU ratings, visual turfgrass quality (TQ), total

shoot chlorophyll concentration, and root total non-structural carbohydrates (TNC).

Spring green-up was visually recorded every 3- to 4-days once green tissue emerged

using a scale of 0 -100% with 0% = complete brown turfgrass and 100% = complete

green turfgrass.

Visual TQ scores were rated every 2-weeks from 1 June to 31 July, 2006 and

2007. Turfgrass quality ratings were based on color, density, texture, and uniformity of

the bermudagrass surface and rated from 1 to 9, 1 = brown, dead turfgrass, 7 = minimal



) was measured end of May and mid-July for both

years. Fresh clippings (minimum 0.1g) were collected from each lysimeter using scissors

and placed in a plastic bag inside a covered bucket to prevent sunlight degradation.

Clippings were weighed (0.1g) and placed in a glass test tube (1.0 cm in width and 14.8

cm in length) with 10 mL of dimethyl sulfoxide (DMSO), which eliminates shoot tissue

80

grinding for chlorophyll extraction (Hiscox and Israelstam, 1979). Samples were

incubated in 65 oC water on a hot plate (PC-600, Corning, Corning, NY) for 1.5-hours

and continuously shaken. Upon completion, samples were passed through filter paper

(Whatman 41, Whatman, England) and remaining extract (2 mL) transferred into

cuvettes. Absorbance values were recorded at 663 nm and 645 nm wavelengths using a

spectrophotometer (GenesysTM

20, ThermoSpectronic, Rochester, NY). Blanks were

initially run and also after every sixth sample. The following formula was used to

calculate total shoot chlorophyll: (mg g-1

) = (8.02 * D663 + 20.2 * D645) * 0.1 (Arnon,

1949).

Root TNC (mg g-1

) was analyzed end of July for both years. Root tissue was

harvested using a bulk density sampler which extracted 154.4 cm3 (10.2 cm in depth)

cores prior to sunrise to minimize any diurnal fluctuations. Following soil removal, root

tissue samples were stored at -75oC until freeze dried at -40

oC for 1-week to cease all

metabolic activity. Samples were then ground using an A-10 plant grinder (IKA Works,

Inc., Wilmington, NC). Grounded samples were rehydrated with 100 L of 80% ethanol

(EtOH) and 2 mL of 0.1 M sodium acetate buffer (pH 4.5) in glass test tubes 13 X 100

mm. Rehydrated samples were placed in boiling water for 1-hour, cooled for 1-hour and

repeated. Then, 2 mL of invertase (Sigma I-4753, 433 units mg-1

) and amyloglucosidase

(Sigma A-7255, 23,000 units g-1

) were added to solution. Samples were placed in a water

bath (40 – 45oC) for 3-days and vortexed three times daily. TNC analysis was analyzed

using Nelson‟s Assay (1944), which determines glucose and fructose in plant tissue

(Nelson, 1944; Somogyi, 1945).A 25 L of aliquot was removed and two reagents

81

(copper and arseno-molybdate) were added to solution. Absorbance values were

measured at 520 nm using a spectrophotometer.

Data Analysis


replications. Treatment effects were evaluated using analysis of variance within SAS

(version 9.1, SAS Institute, Cary, NC). Most SGU ratings showed significant year by

treatment interactions, therefore, data from both years are presented separately.

However, TQ, chlorophyll, and root TNC showed no year by treatment interaction, so

data are pooled for both years. Means separation was analyzed using Fisher‟s least

significant difference (LSD) test at P ≥ 0.05.

Results

Spring Green-Up

In year II, SGU was quicker than in year I, which likely led to a significant year

by treatment interaction. It appears greater soil moisture due to rainfall early in the

spring, not air temperature, may have been a significant factor influencing yearly SGU

results. In March, as cultivars began breaking dormancy, year II had 4.4 cm greater

rainfall than year I (Figure 5.1). Average monthly maximum and minimum temperature

differences between year I and II were minimal (Figure 5.2).

Year I

Overall, 55% continuous shade had minimal impacts on SGU ratings in year I

(Table 5.1). On 4 of the 6 rating dates, Princess 77 had ~92% SGU reduction when

82

Figure 5.1. Monthly precipitation (cm) from 2 March to 31 May 2006 and 2007

and historical averages in Clemson, SC.

Figure 5.2. Average monthly maximum and minimum temperatures (oC) from 2 March to

31 May 2006 and 2007 and historical averages in Clemson, SC.

4.78

10.34 10.269.22

2.77

3.76

13.44

9.3710.69

0

2

4

6

8

10

12

14

16

March April May

2006

2007

Historical average

25 25 26

12 12 14

23 23

27

9 10

15

22 22

26

7 8

13

0

5

10

15

20

25

30

March Apri May March April May

o C

2006 2007 Historical average

Maximum Temperature Minimum Temperature

83

Table 5.1. Spring green-up of six bermudagrass cultivars influenced by various light regimes

(full-sunlight and 55% continuous shade) in spring, 2006.

Spring green-up†

--------24 April------ -----------28 April-------- ----------3 May--------- Bermudagrass

cultivar Sun Shade LSD Sun Shade LSD Sun Shade LSD

TiftNo.4 36.7 60.0 NS 35.0 61.7 NS 58.3 66.7 NS

Tifway 36.7 48.3 NS 45.0 30.0 NS 53.3 53.3 NS

Yukon 26.7 33.3 NS 28.3 40.0 NS 46.7 65.0 NS

Celebration 13.3 26.7 NS 11.7 21.7 NS 21.7 40.0 NS

Riviera 6.3 6.7 NS 5.0 11.7 NS 10.0 13.3 NS

Princess 77 16.7 6.7 NS 18.3 10.0 NS 21.6 8.3 13.09§

LSD NS NS 18.87‡ 34.26 NS 44.08

§

Spring green-up†

--------11 May------ ----------19 May-------- -----------5 June------- Sun Shade LSD Sun Shade LSD Sun Shade LSD

TiftNo.4 63.3 76.7 NS 70.0 73.3 NS 90.0 90.0 NS

Tifway 61.7 46.7 NS 88.3 66.7 NS 88.3 80.0 NS

Yukon 53.3 48.3 NS 60.0 61.7 NS 88.3 76.7 NS


Riviera 21.7 26.7 NS 41.7 33.3 6.54§ 80.0 60.0 NS

Princess 77 31.7 16.7 6.54§ 53.3 33.3 10.35 80.0 51.7 14.63

§

LSD NS 35.33‡ 22.97

‡ NS NS 19.10

‡

†Spring green-up based on a scale of 0-100%, 0% = complete brown turfgrass, 100% =

complete green turfgrass.

‡Values within a column for each rating date followed by the same letter are not significantly

different at P≤0.05 by protected LSD. §Values within a row for each rating date followed by the same letter are not significantly different

at P≤0.05 by protected LSD. LSD = least significant difference, NS = not significant.

grown in shade compared to full-sunlight treatment. Also, Riviera grown in shade had a

25% SGU delay compared to full-sunlight treatment on 19 May.

Under full-sunlight, cultivars SGU by end of May was >80% (Table 5.1). When

bermudagrass cultivars were grown under shade, SGU varied. On 28 April, TiftNo.4 had

a ~3.8 unit SGU increase compared to Celebration, Riviera, and Princess 77. Similarly,

TiftNo.4 increased SGU by ~5.5 and ~2.7 units compared to Riviera and Princess 77 on 3

84

May and 11 May, respectively. By the end of the spring, Princess 77 showed ~60%

greater SGU delay compared to other cultivars.

Year II

In year II, shade-grown Celebration and TiftNo.4 were the only cultivars not to

show significant SGU delays on any rating date compared to full-sunlight treatments

(Table 5.2). Throughout spring, all other cultivars showed significant SGU delays on 2

or more rating dates. On 29 March, shade-grown Tifway and Yukon had 2.5 and 1.2 unit

SGU decrease, respectively, while on 2 April, shade-grown Tifway and Riviera had 0.9

and 1.6 unit SGU decrease, respectively, compared to sun-grown counterparts. Cultivars

SGU were all reduced on 17 April due to unseasonable cold temperatures the preceding

week. Low temperatures from 7 - 12 April averaged below 0oC. However, no freezing

damage was noted as all cultivars recovered when temperatures the following week

reached 27oC. By 9 May, shade-grown Yukon and Riviera had 11% and 50% reduced

SGU, respectively, compared to full-sunlight treatment.

In the absence of shade, few cultivar SGU ratings differences were noted (Table

5.2). On 17 April 2007, Celebration had a 2.2 and 1.3 unit SGU decrease than TiftNo.4

and Yukon, respectively, when grown in full-sunlight. However, all cultivars, when

grown in full-sunlight, were near 100% green by beginning of May. Cultivars SGU

ratings significantly varied when grown under shade. On 2 April, TiftNo.4 and

Celebration had ~0.9 and ~1.1 unit SGU increase compared to Tifway, Riviera, and

Princess 77. TiftNo.4 had ~56% greater SGU on 24 April than Tifway, Riviera, and

85

Table 5.2. Spring green-up of six bermudagrass cultivars influenced by various light regimes

(full-sunlight and 55% continuous shade) in spring, 2007.

Spring green-up†

---------26 March------ --------29 March------- -------2 April------- Bermudagrass

cultivar Sun Shade LSD Sun Shade LSD Sun Shade LSD

TiftNo.4 28.3 21.7 NS 46.7 46.7 NS 76.7 65.0 NS

Tifway 13.3 10.0 NS 35.0 10.0 13.91§ 65.0 35.0 29.98

§

Yukon 21.6 6.7 13.08§ 63.3 28.3 30.69 73.3 46.7 NS


Riviera 30.0 10.0 NS 50.0 26.7 NS 73.3 28.3 35.54

Princess 77 11.7 11.7 NS 25.0 23.3 NS 46.7 38.3 NS LSD NS NS NS 21.69

‡ NS 26.44‡

Spring green-up†

---------17 April-------- ---------24 April------- --------9 May---------

Sun Shade LSD Sun Shade LSD Sun Shade LSD

TiftNo.4 31.7 48.3 NS 91.7 90.0 NS 98.3 98.3 NS

Tifway 16.7 25.0 NS 83.3 60.0 16.68§ 93.3 70.0 NS

Yukon 23.3 31.7 NS 88.3 73.3 NS 98.3 88.3 6.54§

Celebration 10.0 31.7 4.63§ 76.7 71.7 NS 95.0 90.0 NS

Riviera 15.0 11.7 NS 86.7 53.3 20.69 90.0 60.0 26.58

Princess 77 13.3 11.7 NS 85.0 60.0 17.9 93.3 91.7 NS LSD 12.23

‡ 20.76 NS 21.58‡ NS 14.97

‡ †Spring green-up based on a scale of 0-100%, 0% = complete brown turfgrass,

100% = complete green turfgrass. ‡Values within a column for each rating date followed by the same letter are not significantly

different at P≤0.05 by protected LSD. §Values within a row for each rating date followed by the same letter are not significantly different at

P≤0.05 by protected LSD. LSD = least significant difference, NS = not significant.

Princess 77. By 9 May, Riviera and Tifway had ~54% and ~32% greater SGU delay than

TiftNo.4, Yukon, Celebration, and Princess 77.

Turfgrass Quality

Celebration did not show a significant TQ decline throughout summer when

grown under 55% continuous shade (Table 5.3). Compared to full-sunlight, TiftNo.4 had

86

a TQ decline on one rating date, Princess 77 on four rating dates, while Tifway, Yukon,

and Riviera had a TQ decline on all rating dates from 1 June to 31 July when grown

under shade. Compared to full-sunlight, Tifway had the greatest TQ decline (2.5 units),

followed by Yukon (2.2 units), Riviera (1.8 units), Princess 77 (1.5 units), and TiftNo.4

(1.4 units) when grown under shade by 31 July (Illustration D.10).

Sun-grown cultivars showed few significant TQ differences throughout the

summer (Table 5.3). By 31 July, all cultivars TQ were above minimal acceptable

threshold of 7. Bermudagrass cultivar differences when grown under shade occurred on

all rating dates. On 15 June, TiftNo.4 (7.2) and Celebration (6.8) maintained greater TQ

compared to other cultivars when grown under shade, however, Tifway (6.2), Riviera

(5.8), Yukon (5.8), and Princess 77 (5.5) performed similarly. TiftNo.4 and Celebration

show ~1.7 and ~1.3 unit TQ increase, respectively, compared to other cultivars during

July. At the end of July, Princess 77 (5.8) had higher TQ scores than Yukon (5.0), while

Tifway and Riviera had same TQ score of 5.5. By 31 July, regardless of a cultivars

performance under shade, all cultivars TQ was below the minimal acceptable threshold of

7.

Chlorophyll and root total non-structural carbohydrates

In May, cultivars grown under shade had chlorophyll increases compared to full-

sunlight grown cultivars (Table 5.4). Only Princess 77 and Yukon chlorophyll

concentration remain unchanged in May, while other shade-grown cultivars increased

chlorophyll ~26% compared to full-sunlight. In July, shade-grown TiftNo.4 and

87

Table 5.3. Turfgrass quality of six bermudagrass cultivars influenced by various light

regimes (full-sunlight and 55% continuous shade) from 1 June to 31 July, 2006 and 2007.

Turfgrass quality†

---------1 June------- --------15 June--------- ------1 July------ Bermudagrass

cultivar Sun Shade LSD Sun Shade LSD Sun Shade LSD TiftNo.4 7.5 7.2 NS 7.7 7.2 NS 7.5 7.5 NS

Tifway 7.5 5.8 1.49§ 7.2 5.7 1.09

§ 7.5 6.2 1.33

§

Yukon 6.8 6.0 0.67 7.0 5.7 0.54 7.0 5.8 0.67


Riviera 6.8 5.8 0.86 7.0 5.2 0.77 6.8 5.8 0.54

Princess 77 6.5 5.8 NS 6.8 5.7 0.67 6.7 5.5 0.77

LSD NS 0.79‡ NS 0.69

‡ NS 0.74

‡

Turfgrass quality†

----------15 July------- ------31 July-------

Sun Shade LSD Sun Shade LSD

TiftNo.4 7.5 7.7 NS 8.2 6.8 0.86§

Tifway 7.5 6.2 1.15§ 8.0 5.5 0.67

Yukon 7.0 5.5 0.77 7.2 5.0 0.67

Celebration 7.7 7.0 NS 7.7 6.7 NS

Riviera 7.0 5.5 0.86 7.3 5.5 1.02

Princess 77 6.8 5.3 0.67 7.3 5.8 0.54

LSD NS 0.77‡ 0.72

‡ 0.74

†Turfgrass quality based on a scale of 1-9, 1=brown/dead turfgrass, 7=minimally acceptable

turfgrass, 9=healthy/green turfgrass. ‡Values within a column for each rating date followed by the same letter are not significantly

different at P≤0.05 by protected LSD. §Values within a row for each rating date followed by the same letter are not significantly

different at P≤0.05 by protected LSD. LSD = least significant difference, NS = not significant.

88

Table 5.4. Chlorophyll concentration (mg g-1



) of six bermudagrass cultivars influenced by various

light regimes (full-sunlight and 55% continuous shade) in July, 2006 and 2007.

Chlorophyll (mg g-1

)

-----------------May-------------------- -----------------July--------------- Bermudagrass

cultivar Sun Shade LSD Sun Shade LSD

TiftNo.4 1.80 2.23 0.40‡ 2.07 2.61 0.49

‡

Tifway 1.78 2.26 0.30 2.30 2.38 NS

Yukon 1.74 1.96 NS 2.24 2.31 NS

Celebration 2.27 2.71 0.34 2.53 2.89 0.27

Riviera 1.78 2.35 0.39 2.23 1.94 NS

Princess 77 1.99 2.18 NS 2.18 2.32 NS LSD 0.33

† 0.41 NS 0.43†

TNC (mg g-1

)

------------------July-------------------

Sun Shade LSD

TiftNo.4y 40.1 36.9 NS

Tifway 33.6 31.7 1.34‡

Yukon 35.6 34.9 NS Celebration 37.3 34.7 NS Riviera 36.3 34.2 NS Princess 77 36.7 40.7 NS LSD NS NS †Values within a column for each rating date followed by the same letter are not

significantly different at P≤0.05 by protected LSD. ‡Values within a row for each rating date followed by the same letter are not significantly

different at P≤0.05 by protected LSD. LSD = least significant difference, NS = not significant.

Celebration increased chlorophyll 26% and 14% compared to sun-grown counterparts,

while chlorophyll concentration for other cultivars was not impacted by shade. Root

TNC were minimally impacted by full-sunlight or shade, however, Tifway had a 6% root

TNC decrease in shade compared to full-sunlight.

89

Discussion

Under moderate shade stress, bermudagrass cultivars maintained at fairway height

standards showed minimal negative impacts when transitioning from winter dormancy

into spring. Minimal cultivar differences could have been associated with fertility and

the microenvironment created by shade. Typically, most golf course fairways, sports

fields, and/or home lawns are fertilized with a granular fertilizer at a high rate in the

spring to promote green leaf tissue emergence. However, in this study, cultivars were

supplied with 9.7 kg ha-1

of N weekly using foliar products to ensure uniform coverage.

Therefore, a rapid flush of growth did not occur which may be more representative of a

field environment. Due to slowed growth from low and frequent N rates/applications

(i.e., spoon feeding), excessive tissue removal did not occur, which is typically

detrimental for warm-season turfgrass growth under shade (Beard, 1997). Shade alters a

microenvironment by extending dew durations (Dudeck and Peacock, 1992) and reducing

evapotranspiration (ET) rates (Beard, 1973). While not measured in this study, dew

duration (visual assessment) of cultivars in shade was generally longer than in full-

sunlight. Also, plants may have had access to greater water in the soil due to reduced

water demand of turfgrass grown under shade. Soil moisture is a critical factor for

successful bermudagrass spring transition (McCarty, 2005c). Future studies monitoring

soil water content under shade and evaluating water-use characteristics of turfgrasses

under shade would prove beneficial.

Cultivars SGU least impacted by shade were TiftNo.4 and Celebration, while

Riviera and Tifway showed greatest SGU decline when grown in shade. Previous

90

investigations have also noted these cultivars for relative shade tolerance and sensitivity

compared to bermudagrass industry standards (Gaussoin, 1988; Bunnell et al., 2005c;

Hanna and Maw, 2007; Baldwin et al., 2008). Also, Celebration and TiftNo.4 were able

to maintain near acceptable TQ scores under 55% continuous shade compared to other

cultivars in the summer. Reasons why these cultivars are relatively shade-tolerant

compared to industry standards largely remains unclear. The relatively shade-

tolerantbermudagrasses may more effectively utilize sunflecks (Sage and McKown,

2006) or maintain a more horizontal growth habit (minimizing excessive tissue removal)

under shade due to plant hormone manipulation. Future anatomical, morphological, and

physiological studies comparing relatively shade-tolerant and sensitive bermudagrass

cultivars would provide insight into why Celebration and TiftNo.4 are superior compared

to industry standards when grown under shade.

Few SGU differences were noted among sun-grown cultivars in both years.

Munshaw et al. (2006) reported Riviera had greater SGU than Tifway and Princess 77,

however, this study was conducted in Blackburg, VA with air temperatures reaching well

below 0oC. It appears the relative cold tolerance of these cultivars probably played a

factor in their SGU performance. Anderson et al. (2007) noted Riviera as a relatively

freeze-tolerant seeded bermudagrass cultivar, while Tifway possessed intermediate cold-

tolerance among vegetative cultivars. Cold-tolerance of these bermudagrass cultivars

was not a factor in this study since air temperatures never reached lethal temperatures of -

5oC to

-12.2

oC (McCarty et al., 2005).

91

Chlorophyll concentrations for several cultivars in May and July increased in

shade compared to full-sunlight. Jiang and Huang (2001) noted chlorophyll increases in

cool-season turfgrasses subjected to an environmental stress. Miller et al. (2005) also

noted minimal reductions in chlorophyll concentrations for „Tifdwarf‟ and „Floradwarf‟

bermudagrass grown under a variety of shaded environments. Bermudagrass decline in

shade is often attributed to reduced lateral stem growth (Beard, 1997), while the

formation of thin, etiolated leaves decreases plant density. Plants grown in shade

typically have larger and fewer chloroplasts than sun-grown plants, thus more chlorophyll

concentrations in individual leaves are noted in shade-grown plants (Boardman, 1977).

Therefore, in this study, while density decreased (i.e., low TQ scores) for bermudagrass

cultivars grown under shade, chlorophyll concentrations of green leaf tissue collected for

chlorophyll analysis (0.1 g of fresh clipping weight) may have possessed greater

chlorophyll due to chloroplast size. Future studies investigating chloroplast development

of shaded bermudagrasses would provide insight into the previous statement.

Conclusion

While TiftNo.4 and Celebration had highest TQ scores throughout the summer,

both cultivars TQ was below acceptable standards by 31 July. However, these cultivars,

as well as other cultivars selected in this study, performance would be improved by plant

growth regulator use (Qian et al., 1998; Qian and Engelke, 1999; Bunnell et al., 2005b;),

minimizing N application rates (Burton et al., 1959; Bunnell et al., 2005b;), mowing

height increases (White, 2004; Bunnell et al., 2005b;), and appropriate water

92

management (Dudeck and Peacock, 1992). In summary, compared to full-sunlight,

TiftNo.4 and Celebration SGU were least affected by shade, Tifway and Yukon SGU

were intermediately reduced by shade, and Riviera and Princess 77 showed greatest SGU

delays when grown under shade.

93

CHAPTER VI

WINTER CULTURAL PRACTICES AND SHADE IMPACTS ON „TIFEAGLE‟

BERMUDAGRASS SPRING GREEN-UP

Introduction

Spring green-up (SGU) is defined as the initial seasonal appearance of green

shoots as spring temperature and moisture conditions become favorable, thus breaking

winter dormancy (Beard, 2005). Delay of SGU often leaves bermudagrass weak with

large bare areas. Spring green-up is often delayed by winter overseeding (Mazur and

Rice, 1999; Horgan and Yelverton, 2001; Liu et al., 2007). In the transition zone,

turfgrass managers are faced with the yearly decision of whether or not to overseed

bermudagrass putting greens to provide financially important winter green color. The

practice of overseeding is detrimental as both species compete for the same resources:

water, nutrients, and sunlight. Also, trees successfully out-compete turfgrasses for these

same essential resources. Previous research has indicated all major bermudagrass putting

green cultivars are sensitive to low light environments (Miller and Edenfield, 2002;

Bunnell et al., 2005a and b; Miller et al., 2005).

Year-round golf course use, increased television coverage of tournaments, and

meeting player expectations often preclude the option of simply leaving brown, dormant

bermudagrass during winter. Traditionally, overseeding bermudagrass with a cool-

season turfgrass has been the most widely used option for a turfgrass manager to provide

acceptable winter color. An alternative gaining popularity to alleviate overseeding and

94

difficult spring transition, is use of turfgrass colorants or dyes (Machi, 2007). Turfgrass

colorant use began in the mid-1950‟s (Kurtz, 2003); however, only a few scientific

reports investigating colorant use as an alternative to overseeding were published

(Younger and Fucbigami, 1958; Van Dam and Kurtz, 1971; Henry and Gibeault, 1985).

Recently, Shearman et al. (2005) noted a turfgrass colorant improved buffalograss

(Buchloe dactyloides [Nutt.] Engelm.) quality and color ratings and also enhanced SGU.

Gilbert and Kopec (2004) also indicated turfgrass colorants enhanced SGU of dormant

„Tifway‟ bermudagrass (Cynodon dactylon). Long et al. (2005) reported colorant use on

a „Champion‟ bermudagrass putting green was a safe and suitable alternative to

overseeding for winter color and playability. Similarly, Liu et al. (2007) indicated

colorants used on a „TifEagle‟ bermudagrass putting green provided comparable winter

color to overseeded bermudagrass. Other advantages of using colorants include cost

reductions. The cost of overseeding is estimated from $500 to over $2000 per acre

(McCarty, 2005), while using colorants reduces this expense by approximately one-half

(Carson, 2004; Van Dam, 1972).

Our objective for this research was to determine the impacts of different cultural

practices (overseed, colorant use, and dormant turfgrass) and shade on TifEagle

bermudagrass spring transition and summer performance.

95


A two-year research project was conducted at the Turfgrass Research Center,

Clemson University, Clemson, SC on TifEagle bermudagrass maintained in lysimeters

40.64 cm in height and 15.24 cm in diameter filled with 30.50 cm of 85:15 sand:peat and

10.16 cm gravel (8 to 10 mm in diameter) to facilitate drainage. A TifEagle

bermudagrass research green was treated with Titan colorant (Burnett Lime Co.,

Campobello, SC) at 2.4 L 100 m-2

first week of December and re-treated first week of

February at the same rate for both years. Also, the TifEagle research green was

overseeded first week of October with Poa trivialis (L.) at a rate of 390 kg pure live seed

ha-1

following standard preparatory steps for overseeding (McCarty, 2005). Plugs of

untreated, overseeded, and colorant-treated TifEagle bermudagrass sod were collected on

8 March 2006 and 15 March 2007 and washed free of soil with roots clipped directly

below the thatch layer prior to treatment initiation. Lysimeters were maintained adjacent

to field research plots to mimic natural climatic field conditions. Shade levels included a

control (full-sunlight) and 55% continuous shade using a neutral density, polyfiber black

shade cloth (Glenn Harp and Sons, Inc., Tucker, GA) initiating moderate shade stress.

Shade structures were metal frames with individual cells measuring 305 cm in width,

height, and length. Shade cloth extended 183 cm down each lysimeter side to prevent

morning or evening sunlight encroachment, and 227 cm below the shade material to

allow adequate air movement. Lysimeters were 81 cm above the ground and ~127 cm

centered from each side of the shade material.

96

Weekly fertilization began 24 April 2006 and 10 April 2007, ending 31 July 2006

and 2007, using a combination of 10N-1.3P-4.2K and 5N-0P-5.8K liquid fertilizers

(Progressive Turf, LLC., Ball Ground, GA) which provided nitrogen (N) at a rate 9.7 kg

ha-1

. For overseed treatments, fertilization was initiated one-week following potting. A

CO2-pressurized backpack sprayer calibrated at 108 gal ac-1

(1010 L ha-1

) was used to

apply all fertility. No fungicides or herbicides were needed. Lysimeters were watered as

needed to prevent wilt and mowed daily at 0.3 cm using handheld 7.2 volt cordless shear

(model #ssc1000, Black and Decker, Towson, MD) with clippings removed.

Data collection

Data collection included SGU, visual turfgrass quality (TQ) ratings, total shoot

chlorophyll, and root total nonstructural carbohydrates (TNC). Spring green-up was

visually estimated every seven to ten days once green tissue emerged using a scale of 0 -

100% with 0% = complete brown bermudagrass and 100% = complete green

bermudagrass. Bermudagrass and P. trivialis were visually separated due to morphology

differences.

Visual TQ scores were rated every two weeks from 1 June to 1 August, 2006 and

2007. Turfgrass quality ratings were based on color, density, texture, and uniformity of

the bermudagrass surface and rated from 1 to 9, 1 = brown, dead turfgrass, 7 = minimal



) was measured end of May and mid-July for both

years. Fresh clippings of bermudagrass were collected from each lysimeter and placed in

a plastic bag inside a covered bucket to prevent sunlight degradation. Clippings were

97

weighed (0.1g) and placed in a glass test tube (1.0 cm in width and 14.8 cm in length)

with 10 mL of dimethyl sulfoxide (DMSO), which eliminates shoot tissue grinding to

extract chlorophyll (Hiscox and Israelstam, 1979). Samples were incubated in 65 oC

water on a hot plate (PC-600, Corning, Corning, NY) for 1.5 hr and continuously shaken.

Upon completion, remaining extract (2 mL) was transferred into cuvettes. Absorbance

values were recorded at 663 nm and 645 nm wavelengths using a spectrophotometer

(GenesysTM

20, ThermoSpectronic, Rochester, NY). Blanks were initially run and after

every sixth sample. The following formula was used to calculate total shoot chlorophyll:

(mg g-1

) = (8.02 * D663 + 20.2 * D645) * 0.1 (Arnon, 1949).

Root TNC (mg g-1

) was analyzed end of July for both years. Root tissue was




oC for one week to cease all




mm. Rehydrated samples were placed in boiling water for 1 hr, cooled for 1 hr and



(Sigma A-7255, 23,000 units g-1

) were added to the solution. Samples were placed in a

water bath (40 – 45oC) for three days and vortexed three times daily. TNC analysis was

analyzed using Nelson‟s Assay (1944), which determines glucose and fructose in plant

tissue (Nelson, 1944; Somogyi, 1945). A 25 L aliquot was removed and two reagents

98

(copper and arsenomolybdate) were added to the solution. Absorbance values were

measured at 520 nm using a spectrophotometer.

Data Analysis


replications. Results were analyzed using the Statistical Analysis System (SAS) (version

9.1, SAS Institute, Cary, NC). Spring green-up ratings were recorded on different, but

comparable dates each year due to different spring weather patterns for 2006 and 2007.

No meaningful treatment by year interaction was detected SGU ratings or other response

measures; therefore, data for the two years were combined. Mean separation was

performed using Fisher‟s protected least significant difference (LSD) test with = 0.05.

Results

When grown in full-sunlight, quickest SGU ratings were consistently noted for

colorant use on rating dates 20 March to 15 May (Table 6.1). On the first rating date,

colorant treatment showed a 2.7 and 7.3 unit SGU increase compared to full-sunlight

dormant and overseed treatments. Similar trends continued throughout the spring as

colorant use provided greatest SGU ratings compared to dormant and overseed treatments

in full-sunlight (Illustration D.11). Also, dormant bermudagrass showed ~1.1 unit SGU

increase compared to the overseed treatment from week 2 to week 7 when grown in full-

sunlight. No SGU differences were noted between colorant use and dormant

99

Table 6.1. Spring green-up of 'TifEagle' bermudagrass influenced by various winter

cultural practices (colorant, overseed, and dormant) and light intensities (full-

sunlight and 55% continuous shade) recorded from 20 March to 15 May, 2006 and

2007.

-------------------Spring Green-Up (0-100%)†---------------

Light

Treatment

Cultural

Practice Wk 1 Wk 2 Wk 3 Wk 4 Wk 5 Wk 6 Wk 7

Full-

sunlight Colorant 62.5 76.7 76.7 90.0 60.8 87.5 100.0

None 16.7 35.8 42.5 55.8 29.2 68.3 91.7

Overseed 7.5 16.7 25.8 23.3 9.2 31.7 71.7

55%

Shade§ Colorant 29.2 52.5 57.5 65.8 46.7 87.5 100.0

None 16.7 34.2 40.0 44.2 25.0 50.0 93.3

Overseed 2.5 3.3 15.8 16.7 5.0 18.3 51.7

LSD 10.97‡ 10.13 12.56 7.56 7.81 8.18 14.67

†Spring green-up based on a scale of 0-100%, 0% = complete brown turfgrass, 100% =

complete green turfgrass. ‡Values within a column followed by the same letter are not significantly different at

P≤0.05 by protected LSD. §Shade: 55% continuous shade.

LSD = Least significant difference.

bermudagrass by the end of May. When grown in full-sunlight, colorant and dormant

treatments enhanced SGU ~34% compared to the overseed treatment by week 7.

Shade impacted SGU for all treatments on various rating dates (Table 6.1).

Shade-grown colorant-treated TifEagle bermudagrass reduced SGU ~37% from week 2

through week 5 compared to sun-grown colorant treatment. However, colorant treated

TifEagle grown in shade increased SGU ~0.6 and ~7.2 units compared to shade-grown

dormant and overseed treatments from week 1 to week 6, respectively. When

overseeded, shade reduced SGU 4.1, 0.73, and 0.39 units by week 2, 6, and 7,

respectively, compared to the sun-grown overseed treatment (Illustration D.12).

100

Table 6.2. Turfgrass quality of 'TifEagle' bermudagrass influenced by various

winter cultural practices (colorant, overseed, and dormant) and light intensities

(full-sunlight and 55% continuous shade) from 1 June to 1 August, 2006 and

2007.

-----------------Turfgrass Quality

†---------------------

Light

Treatment

Cultural

Practice 1 June 15 June 1 July 15 July 1 August

Full-

sunlight Colorant 7.7 7.8 7.3 8.0 8.0

Dormant 6.7 7.3 7.5 7.3 7.8

Overseed 5.2 4.8 6.0 5.8 5.5

55%

Shade§ Colorant 6.3 7.0 7.2 6.8 6.7

Dormant 5.7 6.5 7.3 6.2 6.2

Overseed 4.5 5.0 5.0 5.2 4.3

LSD 0.77‡ 0.66 0.69 0.79 0.72

†Turfgrass quality based on a scale of 1-9, 1=brown/dead turfgrass, 7=minimally

acceptable turfgrass, 9=healthy/green turfgrass. ‡Values within a column followed by the same letter are not significantly different at

P≤0.05 by protected LSD. §Shade: 55% continuous shade.


With the exception of 1 June rating, summer TQ scores remained similar for sun-

grown colorant and dormant treatments (Table 6.2). However, when winter overseeded,

full-sunlight TQ scores were ~2.3 and ~1.9 units lower than colorant and dormant

treatments, respectively, on all summer rating dates. No TQ differences were noted

between shade-grown colorant and dormant treatments from 15 June to 1 August.

Overseeded TifEagle bermudagrass grown under shade had ~2.0 and ~1.7 unit TQ

decrease compared to shade-grown colorant and dormant treatments, respectively, on all

TQ rating dates. By the end of the study, all treatments grown in shade were below

101

acceptable threshold of 6 and were significantly reduced compared to their full-sunlight

counterparts. Also, winter overseeded TifEagle TQ never surpassed the acceptable

threshold of 7, regardless of light environment.

Dormant TifEagle bermudagrass grown in shade had a 14% chlorophyll increase

compared to its sun-grown counterpart in May (Table 6.3). Light environment did not

impact chlorophyll concentration of colorant or overseed treatments. In full-sunlight,

colorant treatment had 20% greater chlorophyll than overseed, while in shade, a 50%

chlorophyll increase was noted for colorant treatment compared to the overseed

treatment. No differences were noted for July chlorophyll. In full-sunlight, colorant and

dormant treatments had ~62% greater root TNC than the shaded overseed or shade-grown

dormant treatment. Overseeded TifEagle grown in full-sunlight had a 49% root TNC

increase compared to its shade counterpart. Other cultural practices showed no root TNC

differences between sunlight and shade treatments.

Discussion

Historically, warm-season turfgrass managers provided adequate and acceptable

winter color and cover by overseeding with a cool-season turfgrass, often with spring

transition problems. Our results strongly suggest overseeding a TifEagle bermudagrass

green should be avoided, especially when shade is problematic. The overseeded turfgrass

was persistent and competitive through the end of May. In this study, no cultural or

chemical means were attempted to remove the overseeded turfgrass. Also, Poa trivialis

is considered a relatively shade tolerant species due to its origin in Northern Europe

102




) of 'TifEagle' bermudagrass influenced by various

winter cultural practices (colorant, overseed, and dormant) and light intensities

(full-sunlight and 55% continuous shade) in May and July, 2006 and 2007.

Chlorophyll (mg g

-1)

TNC

(mg g-1

)

Treatment Cultural Practice May July July

Full-sunlight Colorant 2.47 2.88

42.18

Dormant 2.35 3.09

37.81

Overseed 2.06 2.94

37.32

Shade‡ Colorant 2.67 3.00

33.61

Dormant 2.68 2.99

27.09

Overseed 1.78 2.99

25.03

LSD 0.31† NS 11.65

†Values within a column followed by the same letter are not significantly different at

P≤0.05 by protected LSD. ‡Shade: 55% continuous shade.


NS = not significant

(McCarty, 2005). Therefore, overseeding transition may be improved if appropriate

cultural and chemical practices were utilized. Previous research indicates various cultural

and chemical means to remove an overseeded turfgrass has both positive and negative

impacts on bermudagrass spring transition (Mazur and Wagner 1987; Horgan and

Yelverton, 2001; Mitra et al., 2008).

Colorant-treated shade-grown TifEagle bermudagrass showed significantly

greater SGU enhancement compared to sun-grown dormant and overseeded TifEagle

bermudagrass on most rating dates (Table 1). This can be attributed to at least two

factors: soil moisture content and surface/soil temperatures. While these parameters were

103

not measured in this study, Liu et al. (2007), Long et al. (2005), Shearman et al. (2005),

and Gilbert and Kopec (2004) attributed enhanced colorant-treated TifEagle and

Champion bermudagrass, buffalograss, and Tifway bermudagrass SGU to increased soil

or surface temperatures. Also, turfgrasses under shade have lower evapotranspiration

rates and cooler temperatures (Beard, 1973). Soil moisture and temperatures are two

critical factors for adequate bermudagrass spring transition (McCarty, 2005). The

combination of warmer surface/soil temperatures from the colorant and increased soil

water content due to reduced ET under shade contributed to quicker bermudagrass SGU.

The previous statement is beyond the scope of this project, however, future field

evaluations are necessary to determine if colorant use can slightly mitigate bermudagrass

shade stress when transitioning from winter dormancy.

Dormant TifEagle grown in shade showed greater chlorophyll concentration than

full-sunlight dormant treatment. Previous reports have also noted chlorophyll increases

under environmental stresses, such as shade and drought (Jiang and Huang, 2001;

Baldwin et al., 2008). Boardman (1977) indicated shade plant leaves typically have

larger, but fewer chloroplasts that contain greater chlorophyll concentrations than sun-

grown plant leaves. Also, plants grown in shaded environments typically have thinner

and etiolated leaves. In this study, while TifEagle shoot density was visually low in

shade, only a small amount of green tissue (0.1 g) was collected for chlorophyll analysis,

which may have contained a greater amount of chlorophyll than sun-grown treatments.

Therefore, in this study, chlorophyll was a poor indicator of TifEagle bermudagrass TQ

and density when grown in shade.

104

Winter cultural practices and light environment negatively influenced TifEagle

bermudagrass summer root carbohydrate reserves. When overseeded and grown in

shade, TifEagle root TNC was significantly lower compared to most other treatments.

This is probably attributed to root competition and additional light interruptions to

TifEagle provided by Poa trivialis root system and canopy. However, no root TNC

differences among any winter treatments when grown in full-sunlight were noted. Unlike

perennial ryegrass (Lolium perenne L.) cultivars, which possess improved heat and

drought tolerance, Poa trivialis is relatively heat sensitive and in this study, was less

persistent when grown in full-sunlight compared to shade. Root carbohydrate data most

likely indicates that reduced competition from Poa trivialis roots and overhead canopy

existed in full-sunlight, which led to minimal carbohydrate differences for sun-grown

treatments.

Conclusion

Based on this study, along with other recent studies (Gilbert and Kopec, 2004;

Long et al., 2005; Shearman et al., 2005; Liu et al., 2007), it appears colorant use will

become a permanent management practice in the turfgrass industry. While colorant use

seems promising, challenges remaining include educating and easing public

perceptions/concerns about playing on a colorant-treated surface, longevity of colorants,

continued colorant production that mimics natural turfgrass color, colorant application

rates, frequency, and timing, and proper colorant application equipment to achieve

uniformity (i.e., nozzles, sprayer type, nozzle distance from surface, etc…..).

105

CHAPTER VII

MANAGEMENT PRACTICES TO ENHANCE „CHAMPION‟ BERMUDAGRASS

PUTTING GREEN UNDER SHADE

Introduction

Sound agronomic practices are essential for successful turfgrass management.

Three essential turfgrass cultural practices are nutrition, water, and mowing. Appropriate

management of these cultural practices is vital for a healthy, vigorous turfgrass stand,

especially in an unfavorable microenvironment, such as reduced light. Sound agronomic

practices can mask and at times, improve turfgrass response when environmental stresses

exist. When sunlight is limited, appropriate fertility, plant growth regulator (PGR) use,

and mowing practices are critical for successful turfgrass culture.

Nitrogen is perhaps the most dynamic and important nutrient for turfgrasses

because it improves color, density, recuperative ability, and plant health when applied at

adequate rates (Liu et al., 2008). A reduction of nitrogen (N) will enhance a turfgrass

stand when light interception is limited. Burton et al. (1959) reported high N (726 kg ac-

1) in 64% shade decreased „Coastal‟ bermudagrass (Cynodon dactylon L.) carbohydrates

30% and decreased plant density and leaf area compared to low N (90 kg ac-1

). Bunnell

et al. (2005b) also noted a 39% TNC reduction in heavily shaded „TifEagle‟

bermudagrass with additional N (24.5 kg ha-1

(NH4)2SO4). Stanford et al. (2005) noted

„Tifdwarf‟ bermudagrass internode and leaf length significantly increased when

photosynthetic photon flux density (PPFD) was reduced from 975 to 300 mol m-2

s-1

.

106

Also, applications of N at 8.1 kg ha-1

wk-1

significantly reduced leaf length, internode

length, and above ground dry matter of Tifdwarf bermudagrass compared to 24.4 kg N

ha-1

wk-1

(Stanford et al., 2005). Therefore, reduced N rates should enhance turfgrass

performance in shade by reducing above ground vertical growth. Similar trends are also

noted for cool-season turfgrasses grown under shade (Schmidt and Blaser, 1967; Bell and

Danneberger, 1999b; Goss et al., 2002).

Trinexapac-ethyl (TE) has become a routine management practice for turfgrass

managers. Since TE inhibits GA20 to GA1 production, vertical shoot growth is slowed

(Adams et al., 1992). Excessive shoot growth in shade rapidly depletes plant

carbohydrate reserves resulting in turfgrass thinning and TQ decline. Morphological

limitations, such as reduced lateral stem growth inhibit warm-season turfgrass

development when sunlight is blocked (Beard, 1997). Therefore, TE is an effective

management tool to mitigate shade stress because vertical shoot growth is reduced.

„Diamond‟ zoysiagrass (Zoysia matrella (L.) Merr) grown under 86% shade with TE

applied every month at 0.048 kg a.i. ha-1

or every other month at 0.096 kg a.i. ha-1

significantly enhanced turfgrass quality (TQ), root production, root + rhizome tissue

carbohydrates, and photosynthetic efficiency (Qian and Engelke, 1999). Similarly, Qian

et al. (1998) demonstrated TE prolonged Diamond zoysiagrass acceptable TQ (>6) for

134 more days compared to non TE-treated under 88% shade. Also, TE-treated

zoysiagrass had 113% greater TNC and 50% greater canopy photosynthetic rate

compared to non TE-treated (Qian et al., 1998). Bunnell et al. (2005b) noted TifEagle

bermudagrass grown in 4 hours of sunlight showed greater TQ scores and chlorophyll

107

concentration with TE applications (0.0393 kg a.i. ha-1

) every three weeks along with an

increase in mowing height (4.7 mm).

Bermudagrasses have been noted for their poor performance in a shaded

microenvironment. For example, TifEagle bermudagrass requires 32.6 mol m-2

d-1

of

sunlight (Bunnell et al., 2005a), while „Floradwarf‟ and Tifdwarf bermudagrass require

~38.6 mol m-2

d-1

(Miller et al., 2005) of sunlight for an acceptable appearance. Also,

Bunnell et al. (2005c) indicated zoysiagrass was more shade tolerant than bermudagrass,

while Jiang et al. (2004 and 2005) noted seashore paspalum cultivars were more shade

tolerant than selected bermudagrass cultivars. Although bermudagrass performs poorly

in shade, superintendents in the eastern part of the transition zone are considering

switching from predominately bentgrass greens to bermudagrass greens in an attempt to

alleviate bentgrass summer stress management challenges (Hartwiger and O‟Brien,

2006). Bentgrass greens are able to grow under moderate shade because they are adapted

to cool, moist climates (McCarty et al., 2005); however, conversion to bermudagrass

greens will be problematic where moderate shade is present. Unless tree removal is a

viable option, shade will be a constraint for growing ultradwarf bermudagrass.

Therefore, sound management practice recommendations will become more important

enabling superintendents to appropriately manage bermudagrass greens under shade.

Champion bermudagrass is gaining popularity as a golf course putting green,

however, field research of Champion bermudagrass response to shade is unknown.

Results from this research benefits superintendents in many aspects. First, this study

provides insight into the performance of Champion bermudagrass when grown under

108

shade in the field. Secondly, this research informs superintendents how to effectively

manage N when growing an ultradwarf bermudagrass cultivar when shading is prevalent.

Thirdly, the interactive effects of TE, various N rates, and Iron (Fe) were examined in a

reduced light environment. Finally, the effect of various N rates, TE, Fe, and various

light intensities were investigated to determine its effect on Champion bermudagrass

thatch accumulation over this two-year study period.


This research project was conducted at the Turfgrass Research Center, Clemson

University, Clemson, SC on Champion bermudagrass (Brown et al., 1997) field research

plots established by sprigs in July, 2003 with soil profile constructed to approximate

United States Golf Association (USGA) recommendations (USGA, 1993) (Illustration

D.13). Shade treatments consisted of control (no shade) and 55% full-day shade using a

neutral density, polyfiber black shade cloth (Glenn Harp and Sons, Inc., Tucker, GA)

supported by polyvinyl chloride (PVC) 183 cm in length and 152 cm in width with 2.54

cm diameter PVC pipes. Shade structures were 15 cm above the bermudagrass surface to

reduce early morning and late afternoon sunlight encroachment, yet maintain adequate

wind movement. Shade treatment duration was 15 June to 15 September 2006 and 2007.

All tents were removed nightly.

Nitrogen was applied every two weeks as urea (45-0-0) using a CO2–pressurized

backpack sprayer at rates of 147, 294, and 441 kg ha-1

yr-1

. Iron was tank mixed with N

at a rate of 2.7 kg a.i. ha-1

2wk-1

. Additional phosphorus (P) and potassium (K)

109

requirements were provided by potassium phosphate (K2HPO4) applied at 98 kg K ha-1

in

July, August, and September. Trinexapac-ethyl was applied at 0.02 kg ha-1

using the

emulsifiable concentrate (11.3% a.i.) every two weeks from 15 June to 31 August 2006

and 2007 using a CO2–pressurized backpack sprayer.

Plots were mowed daily at 3.2 mm throughout the study period. Hollow tine

aerification (1.3 cm diam. tines 10 cm in length with 5.0 cm spacing) occurred late June

and early August for both years. Disease was minimal, therefore no fungicides were

applied.

Data collection

Data collected included microenvironment conditions, visual TQ, clipping yield,

shoot chlorophyll concentration, thatch accumulation, thatch depth, and root total

nonstructural carbohydrates (TNC).

Microenvironment parameters included surface and soil temperature, wind

movement, and light quality and quantity. Surface and soil temperature, light quality,

and PPFD ( mol m-2

s-1

) were recorded on a clear, cloudless day at solar noon using an

indoor/outdoor thermometer (model #1455 and model #9840, Taylor, Oakbrook, IL),

spectroradiameter (Model LI-1800; LiCor, Inc., Lincoln, NE), and quantum radiometer

(Model LI-250, LiCor, Lincoln, NE), respectively. Wind movement was recorded twice

on days with a consistent breeze using an anemometer (model #CS-800, Clark Solutions,

Hudson, MA).

Visual TQ ratings were recorded day 1, week 4, 8, and 12 based on color, density,

texture, and uniformity of the bermudagrass surface. Quality was visually evaluated from

110

1 to 9, 1 = brown, dead turfgrass, 6 = minimal acceptable turfgrass, 9 = ideal green,

healthy turfgrass.


) was collected at week 6 and 12 for both years. Shoot tissue

was collected using a Toro® walk behind greens mower (Greenmaster® 800, The Toro

Company, Bloomington, MN) following one day of growth. Following clipping

collection, clippings were oven dried at 80oC for 48 hr and weighed to quantify shoot

production.

Shoot chlorophyll (mg g-1

) concentration was collected on same dates as clipping

yield. Fresh clippings were collected (as described above) from each plot and

immediately placed in a plastic bag inside a covered bucket to prevent sunlight

degradation. Clippings were weighed (0.1g) and placed in a glass test tube (1.0 cm in

width and 14.8 cm in length) with 10 mL of dimethyl sulfoxide (DMSO) to eliminate

shoot tissue grinding (Hiscox and Israelstam, 1979). Samples were incubated in 65 oC


Upon completion, samples were passed through filter paper (Whatman 41, Whatman,

England) and remaining extract (2 mL) transferred into cuvettes. Absorbance values

were recorded at 663 nm and 645 nm wavelengths using a Spectrophotometer

(GenesysTM

20, ThermoSpectronic, Rochester, NY). Blanks were initially run and also

after every sixth sample. The following formula was used to calculate total shoot

chlorophyll: (mg g-1

) = (8.02 * D663 + 20.2 * D645) * 0.1 (Arnon, 1949).

Thatch accumulation (g) and depth (cm) were measured at week 12 for both

years. A bulk density sampler extracted one 154.4 cm3 core from each plot. Roots were

111

clipped at the base of the thatch layer and the remaining thatch sample was placed in an

80oC oven for 96 hrs and weighed. Thatch samples were then placed in a muffle furnace

(Benchtop Muffle Furnace LMF-A550, Omega Engineering, Inc., Stamford, CT) at

525oC for three hrs to provide ash organic weight (Snyder and Cisar, 2000). Samples

were weighed again and then subtracted from the original dry weight, which determined

thatch accumulation (g). Thatch depth (cm) was measured from five points on the soil

core and averaged using a ruler. Measurements were taken from bottom of the foliage to

the base of the thatch layer. Measurements were collected following oven drying.

Root TNC (mg g-1

) was collected at week 12 for both years. Root tissue was

harvested using a bulk density sampler which extracted 154.4 cm3 cores prior to sunrise

to minimize any diurnal fluctuations. Following soil removal, root tissue samples were

stored at -75oC until freeze dried at -40

oC for two wks to cease all metabolic activity.

Samples were then ground using an A-10 plant grinder (IKA Works, Inc., Wilmington,

NC). Grounded samples were rehydrated with 100 L of 80% ethanol (EtOH) and 2 mL

of 0.1 M sodium acetate buffer (pH 4.5) in glass test tubes 13 X 100 mm. Rehydrated

samples were placed in boiling water for 1 hr, cooled for 1 hr and repeated. Then, 2 mL

of invertase (Sigma I-4753, 433 units mg-1

) and amyloglucosidase (Sigma A-7255,

23,000 units g-1

) were added to solution. Samples were placed in water bath (40 – 45oC)

for three days and vortexed three times daily. TNC analysis was analyzed using Nelson‟s

Assay (1944), which determines glucose and fructose in plant tissue (Nelson, 1944;

Somogyi, 1945). A 25 L of aliquot was removed and two reagents (copper and arseno-

112

molybdate) were added to solution. Absorbance values were measured at 520 nm using a

spectrophotometer.

Data Analysis

Treatments were arranged in a randomized complete block design (RCBD) with

level of shade as a split-plot with three replications. Treatment effects were evaluated

using analysis of variance within the Statistical Analysis System (version 9.1, SAS

Institute, Cary, NC). Linear and quadratic responses were also examined when

appropriate to determine the impacts of light environment, N rates, and TE on parameters

measured. By week 4 of the study, all parameters (TQ, clipping yield, chlorophyll,

thatch, and TNC), did not have significant interactions between year I and II, therefore,

yearly data were pooled and statistically analyzed. Means separation was analyzed using

Fisher‟s least significant difference (LSD) test at P ≥ 0.05.

Results and Discussion

Microenvironment

Surface temperature under shade was reduced 7.8oC (45.4

oC in full-sunlight; 37.6

oC in 55% shade), while soil temperature under shade was reduced 2.2

oC (32.9

oC in full-

sunlight; 30.7 oC in 55% shade) compared to full-sunlight. Light intensity was reduced

by 55% (1891.4 mol m-2

s-1

full-sunlight; 833.9 mol m-2

s-1

55% shade) under the

shading material, however, no differences in light quality or wind movement were

detected due to shade structures position above the bermudagrass surface. Although light

113

quality impacts turfgrass growth (Wherley et. al., 2005), the focus of this study was light

quantity reduction.

Turfgrass Quality

Iron applications had minimal impacts on TQ, however, at week 4, main effect

means indicated Fe (5.9) improved TQ compared to untreated (5.6) plots (Table 7.1).

Munshaw et al. (2006) also noted Fe applications on field grown bermudagrass cultivars

were largely ineffective in consistently enhancing color and quality. However, Xu and

Mancino (2001) reported that applying Fe consistently increased two cool-season

turfgrasses leaf color. The ineffectiveness of Fe to provide increased TQ scores may be

related to daily clipping removal. Symptoms of Fe deficiency are often linked to sites

where daily mowing occurs (Turgeon, 2005). Also, Fe is quickly converted to insoluble

forms in the soil, which typically results in short-term visual responses following Fe

applications (Turgeon, 2005). At week 4, a linear response indicated that increasing N

under 55% full-day shade negatively impacted TQ scores. However, in the absence of

shade, increasing N rates linearly increased visual TQ scores. Applying N at 147 kg ha-1

yr-1

had an unacceptable TQ score of 5.4 in full-sunlight. Long (2006) also indicated

applying N at or below 488 kg ha-1

yr-1

resulted in poor TQ. After two TE applications,

minimal impacts on TQ scores were noted when grown under shade. A linear response

indicated TE significantly increased TQ of sun-grown Champion bermudagrass.

By week 8, applying N at a rate of 147 kg ha-1

yr-1

had greatest TQ compared to

293 and 437 kg ha-1

yr-1

N rates when grown in shade (Table 7.1) (Illustration D.14).

Although TQ scores were improved with lower N rates, TQ was below acceptable

114

Table 7.1. Turfgrass quality of a ‘Champion’ bermudagrass putting green

collected at day 1, weeks 4, 8, and 12 in response to three nitrogen rates (147, 294,

and 441 kg ha-1

yr-1

), plant growth regulator regimes (trinexapac-ethyl at 0 and

0.02 kg ha-1

2 wk-1

), iron applications (0 and 2.7 kg Fe ha-1

2wk-1

), and two light

environments (full-sunlight and 55% full-day shade) at Clemson University,

Clemson, SC in 2006 and 2007.

Light

Environment

Nitrogen

(N) Trinexapac-ethyl

(TE) Wk 4 Wk 8 Wk 12 kg ha-1

yr-1

Shade (S) 147

5.3 5.4 5.6

294

5.2 4.4 4.8

441

4.8 3.2 3.8

Full-sun (FS) 147

5.4 6.4 6.5

294

6.7 7.4 7.4

441

7.2 7.6 7.6

S

TE 5.1 5.1 5.7

No TE 5.0 3.5 3.8

FS

TE 6.8 7.0 7.4

No TE 6.0 7.3 7.0

S

0.0001 0.0001 0.0001

N

0.0003 0.0055 0.0005

TE

0.0101 0.0001 0.0001

S X N

0.0001 0.0001 0.0001

Linear S 0.0043 0.0001 0.0001

FS 0.0001 0.0001 0.0001

Quadratic S NS NS NS

FS 0.0306 NS 0.1106

S X TE

0.0018 0.0001 0.0001

Linear S NS 0.0001 0.0001

FS 0.0001 NS 0.0371

N X TE

NS NS NS

Linear

-- -- --

S X N X TE

NS NS NS †Turfgrass quality based on a scale of 1-9, 1=brown/dead turfgrass, 6=minimally acceptable

turfgrass, 9=healthy/green turfgrass. ‡NS, not significant at 0.05 probability level.

§Significant at 0.05 probability level.

115

threshold for all three N rates. Shade-grown bermudagrass TQ decline below acceptable

standards has also been noted in other field studies (Jiang et al., 2004; Bunnell et al.,

2005 a and b). Similar to week 4, increasing N rates under full-sunlight resulted in a

linear TQ increase. However, results may differ on a golf course due to a high traffic

environment. While the 147 kg ha-1

yr-1

N rate provided acceptable TQ (6.4) in full-

sunlight, this N rate may be too low to provide recuperative ability when exposed to daily

traffic and operations typical of a golf course environment. Long (2006) noted that 488

kg ha-1

yr-1

of N was not sufficient to maintain acceptable TQ. Differences may have

occurred between the studies because Long (2006) used a different N source (ammonium

sulfate) compared to urea used in this study. Also, the green used by Long (2006) was

still in a grow-in phase and may have required a higher annual N input than the

established bermudagrass green used in the present study. Unlike week 4, two months

following shade initiation, TE-treated plots (5.1) showed a linear TQ increase compared

to non TE-treated plots (3.5). However, it should be noted that TQ scores for TE-treated

plots were below the acceptable threshold of 6.

After 3 months of 55% full-day shade, fertilizing with lower N rates provided a

linear TQ increase compared to increasing N rates (Table 7.1). Also, in full-sunlight, a

yearly N rate of 147 kg ha-1

had lower TQ scores than 293 and 437 kg ha-1

yr-1

N rates,

however, all TQ scores remained above acceptable threshold. Trinexapac-ethyl

applications resulted in a linear TQ increase for full-sunlight and 55% full-day shade

plots (Illustration D.15). Bunnell et al. (2005b) noted TE-treated TifEagle bermudagrass

116

mowed at 3.2 mm had greater TQ scores compared to non TE-treated TifEagle when

grown under 4 hours of sunlight.

Clipping Yield

By week 6, under full-sunlight, increasing N rates linearly increased shoot growth

(Table 7.2). Also, when grown under shade at the low N rate, clipping yield was reduced

~93% compared to 293 and 437 kg ha-1

yr-1

N rate. This clipping yield reduction in

response to lower N rates likely led to TQ increases. Beard (1997) suggested a reduction

in lateral stem growth is likely the major factor for warm-season turfgrass decline in

shade. Therefore, in this study, a reduction in shoot growth due to low N rates reduced

the potential for excessive tissue removal, thereby, allowing the plant to conserve and

possibly re-allocate carbohydrate constituents within the plant. Also, TE provided

growth suppression under both full-sunlight and full-day shade environments. Under

55% shade and full-sunlight, TE linearly reduced shoot growth 110% and 63%,

respectively. In full-sunlight, McCullough et al. (2006a and 2007) also noted clipping

yield reductions in field grown TifEagle bermudagrass following TE applications, while

Ervin et al. (2007) noted a reduction in „Tifway‟ bermudagrass plant height when treated

with TE. In shade, Ervin et al. (2002) and Bunnell et al. (2005b) stated TE was effective

in suppressing clipping yield, while Qian et al. (1998) noted a reduction in plant height

following TE applications.

A linear and quadratic clipping yield response was noted as N rates increased

under shade by week 12 (Table 7.2). Also, a linear increase in clipping yield was noted

when grown under full-sunlight when N rates increased from 147 to 437 kg ha-1

yr-1

. At

117

Table 7.2. Clipping yield (g m-2

) of a ‘Champion’ bermudagrass putting green

collected at weeks 6 and 12 in response to three nitrogen rates (147, 294, and

441 kg ha-1

yr-1

), plant growth regulator regimes (trinexapac-ethyl at 0 and 0.02

kg ha-1

2 wk-1

), and two light environments (full-sunlight and 55% full-day

shade) at Clemson University, Clemson, SC in 2006 and 2007.


)

Light

Environment

Nitrogen

(N)

kg ha-1

yr-1

Trinexapac-ethyl

(TE) Week 6 Week 12

Shade (S) -- 12.4

Full-sun (FS) -- 3.5

TE -- 6.4

No TE -- 9.5

S 147 -- 6.4 6.9

294 -- 12.2 15.6

441 -- 12.4 14.6

FS 147 -- 1.2 1.6

294 -- 3.6 3.5

441 -- 5.8 5.4

S -- TE 6.7 --

-- No TE 14.1 --

FS -- TE 2.7 --

-- No TE 4.4 --

--

---------------P-----------

S 0.0001† 0.0001

N 0.0001 0.0001

TE 0.0001 0.0003

S X N 0.0199 0.0051

Linear S 0.0001 0.0001

FS 0.0001 0.0247

Quadratic S 0.0007 0.0013

FS NS‡ NS

S X TE 0.0001 NS

Linear S 0.0001 --

FS 0.0199 --

N X TE NS NS

118


) of a ‘Champion’ bermudagrass putting green

collected at weeks 6 and 12 in response to three nitrogen rates (147, 293, and

437 kg ha-1

yr-1

), plant growth regulator regimes (trinexapac-ethyl at 0 and 0.02

kg ha-1

2 wk-1

), and two light environments (full-sunlight and 55% full-day

shade) at Clemson University, Clemson, SC in 2006 and 2007 (continued).

S X N X TE NS NS †Significant at 0.05 probability level.

‡NS, not significant at 0.05 probability level.

the study‟s end, shaded plots had a 2.5 unit clipping yield increase compared to full-

shoot growth became less pronounced during the study‟s duration. In this study, the last

application of TE was end of August and bermudagrass growth began to naturally

subside during the cooler temperatures and shorter days characteristic of September,

which probably resulted in continued shoot growth reductions. It appears TE‟s effect on

clipping yield suppression efficiency is dependent on turfgrass species, and TE rates and

application frequency (McCullough et al., 2007).

Chlorophyll

Iron did not impact chlorophyll concentration of Champion bermudagrass (Table

7.3). Similar results were noted by Stier and Rogers (2001) when Kentucky bluegrass

(Poa Pratensis L.) and supine bluegrass (Poa supina Schrad.) were subjected to shade

stress. Previous investigations have noted increased Fe availability in nutrient solution

medium enhances chloroplast development of Kentucky bluegrass, which led to an

increase in chlorophyll b production (Lee et al., 1996). In this study, it was possible that

Fe uptake was inhibited, Fe rates and frequency of application were insufficient, or a

reduced light environment restricts optimal Fe uptake. Iron uptake might have occurred,

119

Table 7.3. Total shoot chlorophyll concentration (mg g-1

) of a ‘Champion’

bermudagrass putting green collected at weeks 6 and 12 in response to three

nitrogen rates (147, 294, and 441 kg ha-1

yr-1

), plant growth regulator regimes

(trinexapac-ethyl at 0 and 0.02 kg ha-1

2 wk-1


(full-sunlight and 55% full-day shade) at Clemson University, Clemson, SC in

2006 and 2007.

Chlorophyll (mg g-1

)

Light

Environment

Nitrogen (N)

kg ha-1

yr-1

Trinexapac-

ethyl (TE) Week 6 Week 12

Shade (S) 147 -- 2.88 2.34

294 -- 2.79 1.97

441 -- 2.73 1.94

Full-sun (FS) 147 -- 3.05 2.88

294 -- 3.40 3.02

441 -- 3.56 3.23

S -- TE 3.00 2.21

-- No TE 2.60 1.95

FS -- TE 3.37 2.99

-- No TE 3.32 3.09

-----------------P-------------

S 0.0001† 0.0001

N 0.0161 NS

TE 0.0001 NS

S X N 0.0001 0.0001

Linear S NS‡ 0.0003

FS 0.0001 0.0015

Quadratic S NS 0.0502

FS NS NS

S X TE 0.0023 0.0081

Linear S 0.0001 0.0033

FS NS NS

N X TE NS NS

S X N X TE NS NS †Significant at 0.05 probability level.


120

however, Fe present in shoot tissue may have been removed due to daily mowing. Under

shade, the 147 kg ha-1

yr-1

N rate had 5% greater chlorophyll concentration compared to

the 437 kg ha-1

yr-1

N rate, however, a linear or quadratic response did not occur. A

linear increase in chlorophyll was noted as N rates increased under full-sunlight.

Applying N at 437 kg ha-1

yr-1

provided a 17% and 5% chlorophyll increase compared to

applying N at 147 and 293 kg ha-1

yr-1

, respectively. Applying TE linearly increased

chlorophyll concentration 15% compared to non TE-treated Champion bermudagrass

when grown under 55% full-day shade. Also, TE minimally increased Champion

bermudagrass chlorophyll concentration when grown under full-sunlight compared to

non TE-treated plots.

Unlike week 6, applying N at 147 kg ha-1

yr-1

showed a 21% linear increase in

chlorophyll concentration compared to the 437 kg ha-1

yr-1

N rate at week 12 when grown

under shade (Table 7.3). Also, sun-grown Champion had a linear increase (12%) in

chlorophyll as N rates increased. A linear chlorophyll increase (13%) was noted for TE-

treated plots compared to non TE-treated plots when grown in shade. This increase can

be attributed to a cell length reduction and cell density increase due to TE‟s influence

(Ervin and Koski, 2001). Under full-sunlight, Champion bermudagrass chlorophyll

concentration slightly decreased when TE was applied. However, in week 6, TE-treated

plots had a slight increase in chlorophyll concentration compared to non TE-treated plots.

This data seems to indicate TE applications (0.02 kg ha-1

2 wk-1

) had minimal impacts on

Champion bermudagrass chlorophyll concentrations when grown in full-sunlight.

Bunnell et al. (2005) also noted applying TE from June to August did not significantly

121

increase chlorophyll concentration of sun-grown TifEagle bermudagrass at a 3.2 mm

mowing height. Although, McCullough et al. (2006a) noted an 18% chlorophyll increase

early in the growing season for TE-treated TifEagle bermudagrass compared to non TE-

treated TifEagle, however, TE did not increase chlorophyll concentration at the end of the

growing season. Heckman et al. (2001c) noted a single TE application at multiple rates

enhanced chlorophyll concentration of Kentucky bluegrass (Poa Pratensis L.) cultivars.

It appears that TE initially enhances chlorophyll production early in the growing season,

however, repeated applications throughout the growing season at the same rates may be

less effective at promoting chlorophyll production. This could be attributed to the

dissipation of TE activity when temperatures are high. Beasley et al. (2007) noted in a

cool-season turfgrass that TE uptake was greatest during cooler temperatures, however,

TE dissipation was most rapid in periods of warm temperatures. Qian et al. (1998) noted

TE‟s lasting effect on zoysiagrass shoot height was greatest when temperatures were

cool, while more frequent TE applications were required during periods of high

temperatures. Therefore, in this study, the inability of TE to enhance chlorophyll

production during the growing season could be temperature related. Also, TE applied to

shaded plots consistently maintained higher shoot chlorophyll concentration compared to

non TE-treated plots due to temperature reductions typical of a shaded microenvironment

(Beard, 1973), thereby, possibly influencing TE‟s efficacy. The longevity of TE

enhancing physiological responses of turfgrasses in response to an abiotic stress and/or an

ideal environment may be related to several factors, including soil/surface temperature,

photoperiod, N rate, source, and timing, and TE application rate and frequency.

122

Thatch

Thatch accumulation was minimally impacted by treatments (Table 7.4).

However, Champion grown under shade had a 40% decrease in thatch accumulation

compared to full-sunlight plots. Similar to thatch accumulation, full-sunlight grown

Champion produced 29% greater thatch depth compared to shade grown Champion.

Excessive thatch accumulation typically occurs when organic matter production, such as

clippings or stolons, is greater than organic matter decomposition (Beard, 1973), which is

often linked to accelerated shoot growth. Due to reductions in shoot biomass (Table 7.2)

of shade-grown Champion bermudagrass, this biomass decline most likely led to reduced

thatch accumulation and thickness. Trinexapac-ethyl applications and higher N rates

both resulted in slightly greater thatch depth compared to non TE-treated and lower N

plots. However, Fagerness et al. (2001) indicated repeated TE applications (0.11 kg a.i.

ha-1

) did not affect thatch development, rather increased shoot density, while percent

green canopy tissue accelerated thatch accumulation. In full-sunlight, thatch depth

showed a linear and quadratic response as N rates increased. Nitrogen applied at 293 kg

ha-1

yr-1

showed a 26% and 5% increase in thatch thickness compared to N rates of 147

and 437 kg ha-1

yr-1

, respectively.

Carbohydrates

Root total non-structural carbohydrates were minimally impacted in this study by

N rates or TE applications (Table 7.4). Main effect means noted a 4% increase in root

TNC for Champion bermudagrass grown under full-sunlight compared to shade. Bunnell

123

Table 7.4. Thatch accumulation, thatch thickness, and root total non-structural

carbohydrates of a ‘Champion’ bermudagrass putting green collected at week

12 in response to three nitrogen rates (147, 294, and 441 kg ha-1

2 wk-1

), plant

growth regulator regimes (trinexapac-ethyl at 0 and 0.02 kg ha-1

2 wk-1

), and

two light environments (full-sunlight and 55% shade) at Clemson University,

Clemson, SC in 2006 and 2007.

Light

Environment Nitrogen

(N) Trinexapac-

ethyl (TE)

Thatch

Accumulation

(g)

Thatch

Thickness

(cm)

Root

TNC (mg g

-1)

Shade (S) 5.7 2.8 33.8

Full-sun (FS) 8.0 3.6 35.2 147 -- 2.9 -- 294 -- 3.3 -- 441 -- 3.3 --

TE -- 3.3 --

No TE -- 3.1 --

S 147 -- 2.7 -- 294 -- 2.7 -- 441 -- 2.9 --

FS 147 -- 3.1 --

294 -- 3.9 --

441 -- 3.7 --

----------------------------P----------------------

S 0.0001† 0.0001 0.0238

N NS‡ 0.0082 NS

TE NS 0.0447 NS

S X N NS 0.0221 NS

Linear S -- NS -- FS -- 0.0044 -- Quadratic S -- NS -- FS -- 0.0060 --

S X TE NS NS NS

S X N X TE NS NS NS †Significant at 0.05 probability level.


124

et al. (2005b) reported TifEagle bermudagrass root TNC collected in mid-August grown

under shade varied in response to sunlight hours and management practices.

Conclusion

Champion bermudagrass is unable to provide an acceptable putting green standard

when grown under moderate (55%) full-day shade. However, altering PGR and N

applications enhanced the performance of Champion bermudagrass when grown under

shade. Applying N at 147 kg ha-1

yr-1

significantly improved TQ of Champion when

grown under shade compared to higher N rates. Applying low N rates reduced vertical

shoot growth, thereby, minimizing the amount of shoot tissue removed from daily

mowing. Also, the N rate of 437 kg ha-1

yr-1

reduced shoot chlorophyll 20% compared to

N rate of 147 kg ha-1

yr-1

when grown under shade. Similar to reducing N, applying TE

every two weeks improved TQ and chlorophyll concentrations of shade-grown Champion

bermudagrass.

Based on this study, recommendations for superintendents can be made to manage

bermudagrass greens when light to moderate shade exists. Reducing N rates and

routinely applying TE can improve the performance of Champion bermudagrass in a

shaded environment. However, applying Fe at 2.7 kg a.i. ha-1

2wk-1

had minimal impacts

based on parameters measured. While Champion bermudagrass performance can be

enhanced through management practices, visual TQ will inevitably decline if shade

intensity is too great or shade duration is too long. It has been suggested that

bermudagrass greens require ~36 mol m-2

d-1

of sunlight (Bunnell et al., 2005a; Miller et

125

al., 2005). Also, time of shading is also a relevant consideration when planting a

bermudagrass green (Bunnell et al., 2005a).

126

CHAPTER VIII

ALTERED LIGHT SPECTRAL QUALITIES IMPACTS ON WARM-SEASON

TURFGRASS GROWTH AND DEVELOPMENT

Introduction

Turfgrass growth and development under shade is inhibited by reduced

photosynthesis (Jiang et al., 2004; Miller et al., 2005), increased disease pressure (Beard,

1965; Vargas and Beard, 1981) due to extended morning dew duration (Dudeck and

Peacock, 1992; Williams et al., 1996), reduced carbohydrate production (Bunnell et al.,

2005a; Bunnell et al., 2005c), tree root competition (Whitcomb, 1972; Whitcomb and

Roberts, 1973), and reduced lateral stem growth (Beard, 1997). Another factor limiting

turfgrass growth and development under tree shade is various qualities of light filtered by

trees. The photosynthetic active radiation (PAR) available for plant growth is between

400 and 700 nm with ~90% absorbed by the plant and the remainder reflected at the leaf

surface or transmitted through the leaf (Taiz and Zeiger, 2006). Blue light occurs from

wavelengths 400 to 500 nm, green light 500 to 600 nm, red light 600 to 700 nm, and far-

red light 700 to 800 nm (Taiz and Zeiger, 2006). In nature, trees alter spectral quality

available for turfgrass development (Bell et al., 2000), however, limited research has

investigated the light specific tree species filter in highly maintained turfgrass

environments. Also, most shade research has focused on light quantity by filtering shade

with black neutral cloths (Bell and Danneberger, 1999; Koh et al., 2003; Steinke and

Stier, 2003; Bunnell et al., 2005b; Baldwin et al., 2008).

127

Gaskin (1965) demonstrated a green shade cloth (75% light reduction) had

different light quality spectrums compared to white oak (Quercus alba L.) and maple

(Acer sp.) tree shade. McBee (1969) noted post oak (Quercus stellata Wang.) canopy

filtered wavelengths between 600 to 675 nm. Using a color temperature meter, which

contains two photocells deriving light quality indicating relative amount of blue and red

light, McKee (1963) indicated dense herbaceous shade such as lambsquarter

(Chenopodium album L.), ragweed (Ambrosia trifida L.), and smartweed (Polygonum

pensylvanicum L.) depleted blue wavelengths, while trees with a high canopy filtered red

wavelengths. Bell et al. (2000) noted conifer and deciduous tree shade (R:FR<1.0)

altered spectral quality available for turfgrass growth.

While previous research have demonstrated variations of light available for

turfgrass growth depending on the source of shade, few reports have investigated light

quality impacts for turfgrass growth and development. McBee (1969) noted blue light

minimized stem elongation, while red light enhanced stem elongation for selected

bermudagrass (Cynodon spp.) cultivars. Also, shorter wavelengths (blue light) were most

important for a successful turfgrass stand, while minimal red light was necessary for

normal turfgrass appearance. McVey et al. (1969) also noted blue light significantly

enhanced quality and color while reducing clipping fresh weight production and vertical

shoot elongation in „Windsor‟ Kentucky bluegrass (Poa pratensis L.) and „Tifgreen‟

bermudagrass. In a recent study, Wherely et al. (2005) subjected „Plantation‟ (shade-

tolerant) and „Equinox‟ (shade-sensitive) tall fescue (Festuca arundinacea Schreb.) to

deciduous (Acer spp. and Fraxinus spp., R:FR - 0.428) and neutral (R:FR – 1.021) shade.

128

Both cultivars grown in deciduous shade produced significantly less tillering (~57%),

greater leaf width (~53%), higher chlorophyll levels (~40%), and greater leaf thickness

(~24%) than neutral shade (92% light reduction) grown cultivars. High or low R:FR

ratios did not impact root growth.

It has been noted that changes in spectral light quality influences plant

morphogenesis, while a photosynthetic photon flux density (PPFD) reduction (neutral

shade) affects growth and production parameters (Stuefer and Huber, 1998). However,

physiological and morphological studies of warm-season turfgrasses in response to

various light spectrums are lacking. This type of research could benefit turfgrass

managers in many aspects. First, this study would determine how various spectral

qualities of light affect warm-season turfgrasses performance. This information would

allow turfgrass managers to make informed decisions when trees or tree limbs are

considered for removal. Secondly, this research project would further the understanding

of why warm-season turfgrasses respond differently when grown under shade. Lastly, a

limited number of studies have demonstrated tree species alter light spectral quality in a

turfgrass setting (McKee, 1963; McBee, 1969; Bell et al., 2000). Taking results from

these previous studies and continued research would specify the type of light certain tree

species filter. Therefore, this research is the first step in providing a blueprint for golf

course design by matching turfgrass cultivars that perform well under specific light

filtered by individual tree species. Therefore, the author hypothesized that different light

spectrums, not just light quantity, would alter morphological and physiological status of

129

selected warm-season species to varying degrees and selected turfgrasses would show

genetic differences in response to various light treatments.


This research included two repeated studies at the Clemson University

Greenhouse Research Complex. Study I was conducted from 15 April 2007 – 15 June

2007. Greenhouse conditions averaged 26oC / 22

oC day/night temperature and 60%

relative humidity. Study II was conducted from 6 July 2007 – 31 August 2007.

Greenhouse conditions averaged day/night temperature of 28 oC / 23

oC and 70% relative

humidity.

Each study consisted of five light treatments including a control (full-sunlight)

with three replications in a randomized complete block design. Light treatments include

four different color shade cloths filtering wavelengths 560 - 720 nm (blue shade cloth),

360 – 520 nm (yellow shade cloth), 360 - 560 nm (red shade cloth) and 360-720 (black

shade cloth) (Figure 8.1) (Illustration D.16). Red to far red ratio for each cloth is ~1.171,

while percent light reduction for each cloth was ~65%. Light quality and quantity were

measured on a clear, cloudless day at solar noon using a spectroradiameter (Model LI-

1800; LiCor, Inc., Lincoln, NE), and a quantum radiometer (Model LI-250, LiCor,

Lincoln, NE), respectively.

Turfgrasses selected were „Tifway‟ and „Celebration‟ bermudagrass (Cynodon

dactylon X C. transvaalensis), „Sea Isle 2000‟ seashore paspalum (Paspalum vaginatum

Swartz.), and „Diamond‟ zoysiagrass (Zoysia matrella (L.) Merr). Tifway and

130

Figure 8.1. Portion of light spectrum filtered by the shading material selected for a

greenhouse experiment.

Celebration plugs of sod were collected from the 2002 NTEP bermudagrass trials at the

Clemson University Research Center and washed free of soil with roots clipped. Sea Isle

2000 was provided by Modern Turf (Rembrant, SC 29128). Diamond zoysiagrass was

provided by Atlanta Athletic Club (Johns Creek, GA 30097). All turfgrasses were placed

in lysimeters 15 cm in diameter and 46 cm in height filled with 10.14 cm of gravel (8mm

to 10 mm in diameter) and 30.48 cm of 85% sand and 15% peat as growth media (v:v)

and allowed four weeks to establish before treatment initiation. Lysimeters were mowed

131

every other day at 1.3 cm using a handheld 7.2 volt cordless shear (model #ssc1000,

Black and Decker, Towson, MD) and watered daily (if necessary) to prevent wilt.

During the four-week establishment period prior to shade treatment initiation, fertility

was provided weekly using a combination of 10N-1.3P-4.2K and 5N-0P-5.8K liquid

fertilizers (Progressive Turf, LLC., Ball Ground, GA) at a rate 19.4 kg N ha-1

. Once light

treatments were initiated, turfgrasses were fertilized at a rate of 9.7 kg N ha-1

weekly. A

CO2-pressurized backpack sprayer was used to apply all fertilizers (107 gal ac-1

).

Lysimeters were moved every two weeks to minimize any location effects in the

greenhouse.

Parameters Measured

Data collection included canopy and soil temperature, visual TQ, clipping yield,

lateral spread, total shoot chlorophyll, shoot width, total root biomass, root length

density, specific root length, and root and shoot TNC.

Canopy and soil temperature were recorded on a clear, cloudless day at solar noon

using an indoor/outdoor thermometer (model #1455 and model #9840, Taylor, Oakbrook,

IL).

Visual TQ ratings were measured weekly based on color, density, texture, and

uniformity of the turfgrass surface. Quality was visually evaluated from 1 to 9, 1 =

brown, dead turfgrass, 6 = minimal acceptable turfgrass, 9 = ideal green, healthy

turfgrass.


) was collected at week 2, 4, and 6 following two full days of

growth. Lysimeters were tilted at a 45o angle and mowed with a 7.2 volt cordless shear

132

(model #ssc1000, Black and Decker, Towson, MD). Clippings fell onto poster board

(122 cm by 122 cm) and then placed into brown bags. Turfgrasses were not mowed for

three days prior to collecting clippings. Following clipping collection, clippings were

oven dried at 80oC for 48 hr and weighed to quantify shoot production.

Lateral spread (g) was collected at week 2, 4, and 6. Stolons were allowed to

extend the exterior of the lysimeter for two week periods. Every two weeks, shoot

growth exterior of the lysimeter was collected with a pair of scissors. The collected

biomass was then oven dried at 80oC for 48 hr and weighed.

Shoot width (mm) was measured at weeks 3 and 6. Five fully expanded leaves

from each lysimeter were randomly selected. For each leaf, leaf blade width across the

entire leaf blade was measured 1.5 mm from the base of each individual leaf using a

Buffalo 6” stainless steel digital caliper (Buffalo #SSDC6).


) was collected at weeks 4 and 8. Fresh clippings were

collected from each lysimeter and immediately placed in a plastic bag inside a covered

bucket to prevent sunlight degradation. Clippings were weighed (0.1g) and placed in a

glass test tube (1.0 cm in width and 14.8 cm in length) with 10 mL of dimethyl sulfoxide

(DMSO), which eliminates shoot tissue grinding to extract chlorophyll (Hiscox and

Israelstam, 1979). Samples were incubated in 65 oC water on a hot plate (PC-600,

Corning, Corning, NY) for 1.5 hr and continuously shaken. Upon completion, samples

were passed through filter paper (Whatman 41, Whatman, England) and remaining

extract (2 mL) transferred into cuvettes. Absorbance values were recorded at 663 nm and

645 nm wavelengths using a spectrophotometer (GenesysTM

20, ThermoSpectronic,

133

Rochester, NY). Blanks were initially run and also after every sixth sample. The

following formula was used to calculate total shoot chlorophyll: (mg g-1

) = (8.02 * D663 +

20.2 * D645) * 0.1 (Arnon, 1949).

Total root biomass, root length density (mm cm-3

) (RLD), and specific root length

(cm mg-1

) (SRL) were determined at week 8. Roots were extracted from the entire

lysimeter at washed free of soil using a 1 mm sieve. Once all soil was completely

removed from each soil plug using tap water, roots were clipped from shoot tissue base.

Prior to placing the roots in an oven (80.0 oC) for 48 hr to quantify root biomass, a root

measuring software, WinRhizo Pro (Regent Instruments Inc., Quebec, Qc, Canada),

analyzed scanned root images for RLD and SRL. WinRhizo provides a computerized

method of measuring RLD (total root length (mm) per volume of soil (cm3) as described

by Tennant (1975). For SRL, a ratio of root length to root dry weight was calculated to

determine the amount of root length per milligram of dry weight (cm mg-1

).

Root TNC (mg g-1

) was collected at week 8, while shoot TNC (mg g-1

) was

collected weeks 4 and 8 for both years. Root tissue was harvested using a bulk density

sampler which extracted 154.4 cm3 (10.2 cm in depth) cores prior to sunrise to minimize

any diurnal fluctuations. Following soil removal, root tissue samples were stored at -

75oC until freeze dried at -40

oC for two wks to cease all metabolic activity. For shoot

TNC, shoot tissue was collected prior to sunrise, wrapped in aluminum foil and stored at

75oC until freeze dried at -40

oC for two wks to cease all metabolic activity. Samples

were then ground using an A-10 plant grinder (IKA Works, Inc., Wilmington, NC).

Grounded samples were rehydrated with 100 L of 80% ethanol (EtOH) and 2 mL of 0.1

134

M sodium acetate buffer (pH 4.5) in glass test tubes 13 X 100 mm. Rehydrated samples

were placed in boiling water for 1 hr, cooled for 1 hr and repeated. Two mL of invertase

(Sigma I-4753, 433 units mg-1

) and amyloglucosidase (Sigma A-7255, 23,000 units g-1

)

were then added to solution. Samples were placed in water bath (40 – 45oC) for three

days and vortexed three times daily. TNC analysis was analyzed using Nelson‟s Assay

(1944), which determines glucose and fructose in plant tissue (Nelson, 1944; Somogyi,

1945). For root TNC, 50 L of aliquot was removed, while 100 L of aliquot was

removed for shoot TNC (Waltz, 2005). Then, two reagents (copper and

arsenomolybdate) were added to solution and absorbance values were measured at 520

nm using a spectrophotometer.

Data Analysis

Treatments were arranged in a randomized complete block design with 3

replications. All statistical computations were conducted using analysis of variance

(ANOVA) within the Statistical Analysis System (version 9.1, SAS Institute, Cary, NC).

Means were separated by the Fisher‟s Least Significant Difference (LSD) test with an

alpha of 0.05. Under full-sunlight, significant differences occurred for clipping yield,

lateral spread, shoot width, shoot chlorophyll concentration, and root length density,

therefore, relative values were calculated to determine the impact different types of shade

had on each turfgrass. For root and shoot TNC and SRL, no significant treatment by

species interactions occurred, therefore, main effect means are presented. Data are

pooled for both repeated studies as no significant study by treatment interaction occurred.

135

Results

Microenvironment

Canopy temperature under each shade cloth was reduced 15oC (46

oC in full-

sunlight; 31 oC in shade), while soil temperature under shade cloth was reduced 2

oC (31

oC in full-sunlight; 29

oC in shade) compared to full-sunlight.

Full-sunlight

Turfgrasses performance significantly varied when grown under full-sunlight (Table

1). Tifway produced 50% greater clipping yield than Celebration at week 2, while

similar trends continued in week 4. By week 6, Diamond had greatest clipping yield

(~75%) compared to all other turfgrasses. At week 2, Celebration lateral spread was

60% greater than Tifway, while Diamond and Sea Isle 2000 were similar. By week 6,

Sea Isle 2000 and Celebration had ~1.0 unit lateral spread increase compared to

Diamond and Tifway, respectively. For shoot width, at week 8, Diamond had 160%,

94%, and 69% thinner leaf blade than Sea Isle 2000, Celebration, and Tifway,

respectively. Celebration and Tifway produced ~52% and ~29% greater chlorophyll

concentrations at week 3 compared to Diamond and Sea Isle 2000, respectively. At

week 6, Celebration showed 74% and 34% greater chlorophyll than Diamond and Sea

Isle 2000, respectively. Sea Isle 2000 produced 0.8 unit greater root biomass than

Celebration and ~3.2 unit greater root biomass than Diamond and Tifway (Illustration

D.17). Meanwhile, Celebration showed a ~1.3 unit increase in root biomass compared

to Diamond and Tifway. For RLD, under full-sunlight, Sea Isle 2000 (10.7 mm cm-3

)

136


), lateral spread (g), shoot width (mm), shoot

chlorophyll (mg g-1

), root mass (g m-2

), and root length density (mm cm-3

) of

'Diamond' zoysiagrass, 'Sea Isle 2000' seashore paspalum, 'Celebration'

bermudagrass, and 'Tifway' bermudagrass under full-sunlight.

Clipping

Yield

(g m-2

)

Lateral

Spread

(g)

Shoot

Width

(mm)

Chlorophyll

(mg g-1

)

Root

Mass

(g m-2

)

Root

Length

Density

(mm cm-3

)

Treatment -----------------------------------------Week 2------------------------------------

Diamond† 0.19 0.48 -- -- -- --

Sea Isle

2000 0.15 0.54 -- -- -- --

Celebration 0.16 0.64 -- -- -- --

Tifway 0.24 0.40 -- -- -- --

LSD 0.05‡ 0.17 -- -- -- --

-----------------------------------------Week 3------------------------------------

Diamond -- -- -- 1.76 -- --

Sea Isle

2000 -- -- -- 1.87 -- --

Celebration -- -- -- 2.74 -- --

Tifway -- -- -- 2.34 -- --

LSD -- -- -- 0.42‡ -- --

-----------------------------------------Week 4------------------------------------

Diamond 0.26 0.40 0.39 -- -- --

Sea Isle

2000 0.18 0.53 0.94 -- -- --

Celebration 0.19 0.61 0.85 -- -- --

Tifway 0.25 0.31 0.65 -- -- --

LSD 0.03‡ 0.11 0.10 -- -- --

-----------------------------------------Week 6------------------------------------

Diamond 0.33 0.37 -- 1.71 -- --

Sea Isle

2000 0.16 0.58 -- 2.21 -- --

Celebration 0.16 0.59 -- 2.97 -- --

Tifway 0.23 0.29 -- 2.62 -- --

LSD 0.06‡ 0.11 -- 0.53 -- --

-----------------------------------------Week 8------------------------------------

Diamond -- -- 0.48 -- 0.19 2.6

Sea Isle

2000 -- -- 1.25 -- 0.86 10.7

137


), lateral spread (g), shoot width (mm), shoot

chlorophyll (mg g-1

), root mass (g m-2

), and root length density (mm cm-3

) of


bermudagrass, and 'Tifway' bermudagrass under full-sunlight (continued).

Celebration -- -- 0.93 -- 0.47 6.5

Tifway -- -- 0.81 -- 0.22 3.8

LSD -- -- 0.11‡ -- 0.17 1.20

†Diamond: 'Diamond' zoysiagrass, 'Sea Isle 2000' seashore paspalum, 'Celebration'

bermudagrass, and 'Tifway' bermudagrass. ‡Values within a column followed by the same letter are not significantly different at

P≤0.05 by protected LSD.


had greatest RLD, followed by Celebration (6.5 mm cm-3

), Tifway (3.8 mm cm-3

), and

Diamond (2.6 mm cm-3

).

Shade

Turfgrass Quality

Minimal TQ differences were noted between turfgrasses maintained in full-

sunlight (Table 8.2). Following 1 wk of shade, Tifway was the only turfgrass to drop

below the acceptable threshold of 6. Celebration grown under black shade decreased TQ

by ~0.6 units compared to other shading material. Diamond and Sea Isle 2000 did not

show any significant TQ decreases compared to full-sunlight treatment. Comparing

turfgrasses, Diamond and Sea Isle 2000 had greater TQ scores than the bermudagrass

cultivars for most shade treatments. Also, Celebration produced greater TQ than Tifway

under yellow (1.0 unit) and blue (1.0 unit) shade.

By week 4, all turfgrasses TQ began to decline in response to shade (Table 8.2).

Only Diamond was able to remain above the acceptable threshold of 6 under black shade.

Within each turfgrass, black shade consistently showed greatest TQ declines compared to

138

other shade colors. Yellow, red, and blue shade had similar TQ scores. Celebration

maintained ~1.7 unit greater TQ than Tifway under all shade treatments. Meanwhile, Sea

Isle 2000 had ~0.8 unit TQ increase than Celebration when grown under blue and black

shade.

At the conclusion of the study, Diamond remained above acceptable TQ

threshold, however, a TQ decline was noted compared to full-sunlight (Table 8.2).

Unlike week 4, yellow and red shade TQ were similar for all turfgrasses, however, blue

shade showed ~0.8, ~0.6, ~1.3, and ~1.4 TQ unit decline for Diamond, Sea Isle 2000,

Celebration, and Tifway, respectively, compared to yellow and red shade (Illustration

D.18). Diamond had a 1.8, 3.2, and 4.5 unit greater TQ than Sea Isle 2000, Celebration,

and Tifway, respectively, under black shade. The most shade-sensitive turfgrass was

Tifway as TQ scores were below 4 under all shade treatments.

Clipping Yield

At week 2, black shade reduced Celebration and Tifway clipping yield ~0.63 and

~1.16 units, respectively, compared to yellow, red and blue shade (Table 8.3). Diamond

and Sea Isle 2000 grown under black and blue shade had ~75% and ~52% less clipping

yield compared to yellow shade. Comparing turfgrasses, under yellow and black shade,

Tifway clipping yield was reduced ~0.70 and ~1.26 units, respectively, compared to other

turfgrasses. Meanwhile, Celebration produced 30% and 64% greater clipping yield than

Diamond under red and blue shade, respectively.

139

Table 8.2. Turfgrass quality of 'Diamond' zoysiagrass, 'Sea Isle 2000' seashore

paspalum, 'Celebration' bermudagrass, and 'Tifway' bermudagrass affected by

full-sunlight and various types of filtered light (~65% reduction) in a

greenhouse study.

---------------------------------------Week 2-----------------------------------

Treatment Diamond Sea Isle 2000 Celebration Tifway LSD

Sun† 8.2 7.8 7.8 7.3 NS

Yellow 7.8 7.7 7.0 6.0 0.61§

Red 8.0 7.2 6.8 6.3 0.66

Blue 8.0 7.5 7.0 6.0 0.35

Black 7.8 7.2 6.3 5.8 0.61

LSD NS NS 0.54‡ 0.54

---------------------------------------Week 4-----------------------------------

Sun 8.3 8.2 7.8 7.5 0.56§

Yellow 7.3 6.8 6.2 4.7 0.66

Red 7.7 6.5 6.3 5.0 0.56

Blue 7.5 6.5 5.7 3.3 0.71

Black 6.8 5.5 4.7 3.3 0.66

LSD 0.58‡ 0.49 0.70 0.70

---------------------------------------Week 6-----------------------------------

Sun 8.2 7.8 7.5 7.7 NS

Yellow 7.2 5.7 5.0 3.7 0.61§

Red 7.3 5.8 5.5 4.0 0.66

Blue 6.5 5.2 4.0 2.5 0.75

Black 6.0 4.2 2.8 1.5 0.61

LSD 0.58‡ 0.62 0.62 0.67

†Sun: full-sunlight control, Yellow: filters <520 nm, Red: filters <560nm, Blue:

filters >560, and Black: filters all wavelengths. ‡Values within a column within each week followed by the same letter are not

significantly different at P≤0.05 by protected LSD. §Values within a row within each week followed by the same letter are not

significantly different at P≤0.05 by protected LSD.

Turfgrass quality based on a scale of 1-9, 1=brown/dead turfgrass, 7=minimally

acceptable turfgrass, 9=healthy/green turfgrass.

LSD = Least significant difference, NS = not significant.

140

Table 8.3. Relative clipping yield of 'Diamond' zoysiagrass, 'Sea Isle 2000' seashore

paspalum, 'Celebration' bermudagrass, and 'Tifway' bermudagrass affected by

full-sunlight and various types of filtered light (~65% reduction) in a greenhouse

study.

------------------------------------------Week 2-------------------------------------


Yellow† 119.8 126.8 143.9 76.5 39.54

§

Red 101.1 97.8 131.4 88.2 28.09

Blue 69.3 91.0 114.3 76.3 33.42

Black 67.9 63.2 79.7 31.1 20.58

LSD 19.83‡ 34.91 30.94 36.39

------------------------------------------Week 4-------------------------------------

Yellow 100.9 105.9 110.7 82.4 NS

Red 77.1 90.2 100.1 70.4 NS

Blue 61.2 65.8 71.9 70.7 NS

Black 42.7 33.7 41.2 29.3 NS

LSD 22.94‡ 24.92 31.22 27.80

------------------------------------------Week 6-------------------------------------

Yellow 69.8 102.7 99.9 67.1 27.17§

Red 63.7 86.4 94.9 54.7 20.04

Blue 60.7 74.5 75.7 38.2 28.62

Black 31.3 39.7 36.7 21.4 NS

LSD 17.08‡ 29.32 28.11 17.24

†Yellow: filters <520 nm, Red: filters <560nm, Blue: filters >560, and Black: filters all

wavelengths. ‡Values within a column within each week followed by the same letter are not


§Values within a row within each week followed by the same letter are not significantly



At week 4, no differences were detected between turfgrasses for any shade

treatment (Table 8.3). Black shade reduced Tifway clipping yield ~1.5 units compared to

yellow, red, and blue shade. Also, Diamond showed a 37% (red shade), 63% (blue

shade), and 136% (black shade) clipping yield reduction compared to yellow shade. For

141

Sea Isle 2000, compared to full-sunlight, yellow shade increased clipping yield 6%, while

black shade reduced clipping yield 66%. Similarly, yellow shade increased Celebration

clipping yield 11%, while blue and black shade reduced clipping yield ~44% compared to

full-sunlight.

By week 6, clipping yield differences between yellow and red shade and between

red and blue shade were not detected for any turfgrasses (Table 8.3). However, Tifway

grown under blue shade had a reduced clipping yield 76% compared to yellow shade.

Compared to other shade types, black shade reduced clipping yield ~0.89, ~1.21, and

~1.46 units for Diamond, Sea Isle 2000, and Celebration, respectively. Celebration and

Tifway clipping yield decreased ~10% and ~47% under yellow, red, and blue shade

compared to full-sunlight. Diamond clipping yield reduced ~41% compared to Sea Isle

2000 when grown under yellow and red shade. Meanwhile, Celebration produced 49%,

73%, and 98% greater clipping yield under yellow, red, and blue shade, respectively,

compared to Tifway.

Lateral Spread

At week 2, lateral spread of Diamond grown under shade was not impacted (Table

8.4). For other turfgrasses, lateral spread between yellow and red shade were similar,

while no differences were noted between red and blue shade. However, Celebration and

Tifway lateral spread reduced ~0.65 and ~1.79 units, respectively, under black shade

compared to yellow, red, and blue shade. Sea Isle 2000 grown under red shade had 40%

less lateral spread than yellow shade. Celebration showed 63% and 128% greater lateral

spread than Tifway when grown under red and black shade, respectively. Meanwhile,

142

Table 8.4. Relative lateral spread of 'Diamond' zoysiagrass, 'Sea Isle 2000'

seashore paspalum, 'Celebration' bermudagrass, and 'Tifway' bermudagrass

affected by full-sunlight and various types of filtered light (~65% reduction) in a

greenhouse study.

-----------------------------------------Week 2------------------------------------


Yellow† 101.7 93.4 69.2 57.7 28.87

‡

Red 76.8 90.9 76.9 47.1 27.91

Blue 66.4 66.9 72.5 48.0 NS

Black 73.9 52.8 44.3 19.4 24.76

LSD NS 25.37§ 15.76 20.73

-----------------------------------------Week 4------------------------------------

Yellow 97.1 80.7 65.9 42.4 22.91‡

Red 63.7 61.0 46.3 52.2 NS

Blue 53.9 38.4 39.0 27.7 12.61

Black 47.1 24.6 15.1 15.5 11.12

LSD 25.97§ 14.78 9.78 16.05

-----------------------------------------Week 6------------------------------------

Yellow 99.0 73.3 49.7 52.9 29.16‡

Red 73.0 54.4 40.9 36.3 24.24

Blue 56.9 39.8 32.9 19.1 12.36

Black 40.8 18.5 8.9 6.8 12.36

LSD 30.72§ 20.61 9.34 16.98


wavelengths. ‡Values within a row within each week followed by the same letter are not


§Values within a column within each week followed by the same letter are not



143

Celebration and Sea Isle 2000 lateral spread were similar. Diamond produced ~0.62 and

~1.74 unit greater lateral spread than Celebration and Tifway when grown under yellow

and black shade, respectively.

At week 4, yellow shade-grown Diamond produced greater lateral spread than red

(52%), blue (80%), and black (106%) shade (Table 8.4). Blue shade reduced lateral

spread compared to red shade for Sea Isle 2000 (59%) and Tifway (88%). Blue and

black shade impacted lateral spread similarly for Diamond, Sea Isle 2000, and Tifway,

however, black shade reduced Celebration lateral spread 1.6 units compared to blue

shade. Comparing bermudagrass cultivars, Celebration maintained greater lateral spread

when grown under yellow shade (55%) than Tifway. Under blue and black shade,

Diamond showed ~0.58 and ~1.69 unit greater lateral spread, respectively, than Sea Isle

2000, Celebration, and Tifway. Similar to week 2, lateral spread variation between Sea

Isle 2000 and Celebration did not occur.

At week 8, black shade increased lateral spread 1.2 and 2.7 units for Sea Isle 2000

and Celebration, respectively, compared to blue shade (Table 8.4). Sea Isle 2000 was the

only cultivar where red shade reduced lateral spread (35%) compared to yellow shade.

Compared to black shade, red shade reduced Diamond, Sea Isle 2000, Celebration, and

Tifway lateral spread by 0.81, 1.94, 3.60, and 4.34 units, respectively. When grown

under blue shade, Celebration maintained 72% greater lateral spread than Tifway

bermudagrass. For all other shade treatments, Sea Isle 2000, Celebration, and Tifway

performed similarly. However, Diamond had ~0.93 and ~4.3 unit lateral spread increases

144

than both bermudagrass cultivars when grown under yellow and black shade,

respectively.

Shoot Width

Shade treatments did not impact turfgrasses shoot width at week 4 (Table 8.5).

Also, few differences were noted at week 4 between turfgrasses shoot width. However,

black shade-grown Sea Isle 2000 (23%), Celebration (29%), and Tifway (36%) had shoot

width reductions compared to Diamond. Diamond and Sea Isle 2000 shoot width was not

impacted by shade at week 8. Celebration grown under black shade reduced shoot width

38% and 25% compared to red and blue shade, respectively. For Tifway, yellow shade

showed the least impact (11% reduction) on shoot width relative to full-sunlight, while

other shade treatments averaged a 29% shoot width reduction relative to full-sunlight.

No differences were noted between turfgrasses shoot width by week 8.

Chlorophyll

By week 3, all turfgrasses showed chlorophyll concentration declines relative to

full-sunlight (Table 8.6). Diamond grown under blue shade had 46% and 32%

chlorophyll increase compared to yellow and red shade. Sea Isle 2000 grown under blue

and black shade had 20% and 33% lower chlorophyll concentration, respectively,

compared to yellow shade. When grown under black shade, Celebration and Tifway

chlorophyll concentrations were ~30% and 59% lower, respectively, than when grown

under yellow, red, and blue shade. Diamond grown under yellow shade had ~37% less

chlorophyll than yellow shade-grown Sea Isle 2000, Celebration, and Tifway.

145

Table 8.5. Relative shoot width of 'Diamond' zoysiagrass, 'Sea Isle 2000'

seashore paspalum, 'Celebration' bermudagrass, and 'Tifway' bermudagrass

affected by full-sunlight and various types of filtered light (~65% reduction)

in a greenhouse study.

-----------------------------------------Week 4---------------------------------


Yellow† 88.4 84.3 90.3 77.7 NS

Red 87.7 104.4 136.8 75.4 NS

Blue 84.7 72.3 82.3 65.3 NS

Black 100.1 81.2 77.4 73.4 17.12‡

LSD NS NS NS NS

-----------------------------------------Week 8---------------------------------

Yellow 86.8 84.9 72.4 89.2 NS

Red 89.8 82.3 84.6 75.5 NS

Blue 83.3 76.5 76.6 72.3 NS

Black 81.3 73.9 61.5 65.9 NS

LSD NS NS 12.89§ 12.82

†Yellow: filters <520 nm, Red: filters <560nm, Blue: filters >560, and Black:

filters all wavelengths. ‡Values within a row within each week followed by the same letter are not

significantly different at P≤0.05 by protected LSD. §Values within a column within each week followed by the same letter are not


LSD = least significant difference, NS = not significant.

However, Diamond produced ~27% greater chlorophyll than Sea Isle 2000 and

Tifway when grown under blue shade. Under black shade, Sea Isle 2000 and Celebration

produced ~31% greater chlorophyll than Tifway.

Few chlorophyll differences were noted among turfgrasses by week 6 (Table 8.6).

However, black shade reduced Tifway chlorophyll concentration 43%, 34%, and 13%

compared to yellow, red, and blue shade, respectively. Also, Diamond had 49%, 57%,

and 80% greater chlorophyll than Sea Isle 2000, Celebration, and Tifway, respectively.

146

Table 8.6. Relative shoot chlorophyll concentration of 'Diamond' zoysiagrass, 'Sea

Isle 2000' seashore paspalum, 'Celebration' bermudagrass, and 'Tifway'

bermudagrass affected by full-sunlight and various types of filtered light (~65%

reduction) in a greenhouse study.

----------------------------------------Week 3----------------------------------------


Yellow† 64.7 87.8 91.2 87.2 15.39

§

Red 71.2 77.0 85.9 78.3 NS

Blue 94.2 73.4 84.4 75.4 15.29

Black 81.7 66.0 66.9 50.6 14.75

LSD 17.94‡ 11.60 17.53 15.09

----------------------------------------Week 6----------------------------------------

Yellow 110.1 92.7 90.3 89.4 NS

Red 99.8 82.6 85.1 83.9 NS

Blue 100.1 80.2 87.4 79.1 NS

Black 112.1 75.3 71.6 62.4 28.11§

LSD NS NS NS 16.43‡


wavelengths. ‡Values within a column followed by the same letter are not significantly different at


§Values within a row followed by the same letter are not significantly different at P≤0.05

by protected LSD.


Carbohydrates

Root TNC

Different shade types did not impact root TNC, however, full-sunlight provided

~10% increase in root TNC compared to other light treatments (Table 8.7). Sea Isle 2000

produced greatest root TNC (36.5 mg g-1

), while Diamond (34.1 mg g-1

) and Tifway

(33.8 mg g-1

) showed lowest root TNC values.

147

Table 8.7. Root and shoot total non-structural carbohydrates (mg g-1

) of


bermudagrass, and 'Tifway' bermudagrass affected by full-sunlight and

various types of filtered light (~65% reduction) in a greenhouse study.

Shoot TNC (mg g-1

)

Treatment Root TNC (mg g-1

) Week 4 Week 8

Sun† 37.4 55.6 59.4

Yellow 33.2 50.5 54.3

Red 34.8 48.3 54.6

Blue 33.8 49.0 50.9

Black 34.9 44.1 49.3

LSD 2.37‡ 4.95 4.57

Shoot TNC (mg g-1

)

Turfgrass Root TNC (mg g-1

) Week 4 Week 8

Diamond 34.1 48.6 54.6

Sea Isle 2000 36.5 47.7 57.5

Celebration 34.9 51.1 51.4

Tifway 33.8 50.7 51.3

LSD 2.12‡ NS 4.09

†Sun: full sunlight control, Yellow: filters <520 nm, Red: filters <560nm, Blue:

filters >560, and Black: filters all wavelengths. ‡Values within a column followed by the same letter are not significantly different



Shoot TNC

Full sunlight showed ~16% and ~14% greater shoot TNC at week 4 and 8,

respectively, compared to other light treatments (Table 8.7). At week 4, yellow shade

had 15% greater shoot TNC than black shade, while yellow and red shade had ~11%

greater shoot TNC than black shade by week 8. Turfgrass shoot TNC differences were

not detected at week 4, however, at week 8, Sea Isle 2000 had ~12% greater shoot TNC

than Tifway and Celebration.

148

Specific Root Length and Root Length Density

Diamond and Celebration produced similar SRL, while Tifway bermudagrass

showed ~101% SRL increase compared to Sea Isle 2000 (Table 8.7). Compared to shade

treatments, full-sunlight showed lowest (8.4 cm mg-1

) SRL. Under different types of

light, blue shade had ~48% SRL increase compared to other shade treatments.

Under different types of shade, no RLD differences were noted between

turfgrasses (Table 8.8). However, different light environments impacted RLD for each

turfgrass, except Celebration. Red shade produced a 1.6 and 1.1 unit RLD increase

compared to blue and black shade for Diamond, respectively. Similarly, Sea Isle 2000

grown under red shade had a RLD increase of 24% and 35% compared to blue and black

shade, respectively. However, RLD for Tifway grown under blue shade showed a 3.2

and 2.8 unit decrease compared to yellow and red shade, respectively.

Root Biomass

In response to different types of light, only Diamond showed significant

variations (Table 8.8). Diamond grown under red shade produced 3.6 and 1.5 unit root

biomass increases compared to blue and black shade, respectively. Under yellow and red

shade, Diamond and Sea Isle 2000 performed similarly, while Celebration and Tifway

showed no significant differences. However, Sea Isle 2000 had 1.9 and 4.7 unit root

biomass increases compared to Diamond and Tifway, respectively, when grown under

blue shade.

149

Table 8.8. Total root biomass and root length density of ‘Diamond'

zoysiagrass, 'Sea Isle 2000' seashore paspalum, 'Celebration'

bermudagrass, and 'Tifway' bermudagrass affected by full-sunlight and

various types of filtered light (~65% reduction) in a greenhouse study.

Root Biomass

------------------------------------Week 8----------------------------------


Yellow 54 45 21 22 20.9§

Red 64 48 22 13 35.1

Blue 14 40 27 7 23.5

Black 26 25 12 14 NS

LSD 37.0‡ NS NS NS

Root Length Density

------------------------------------Week 8----------------------------------

Yellow 65.7 46.1 37.9 82.9 NS

Red 82.4 48.8 38.2 76.6 NS

Blue 31.6 39.3 35.8 19.9 NS

Black 38.7 36.1 18.4 36.7 NS

LSD 37.81‡ 9.34 NS 51.38

†Sun: full sunlight control, Yellow: filters <520 nm, Red: filters <560nm, Blue:

filters >560, and Black: filters all wavelengths. ‡Values within a column followed by the same letter are not significantly


§Values within a row followed by the same letter are not significantly different



Discussion

Few previous reports have investigated the morphological and physiological

responses of warm-season turfgrasses to different light spectral qualities. Also, Diamond,

Sea Isle 2000, and Celebration are turfgrasses gaining popularity, however, direct

comparisons of their performance in full-sunlight and shade compared to industry

standards have not been reported. In this study, under full-sunlight and shade, turfgrasses

performance significantly varied. Diamond zoysiagrass was the most shade-tolerant

150

turfgrass species among selected turfgrasses. Diamond zoysiagrass TQ scores were

consistently higher, chlorophyll concentration decreases compared to full-sunlight were

minimal, and lateral spread growth was least impacted by shade compared to other

turfgrasses. Bunnell et al. (2005c) also indicated zoysiagrass was more shade-tolerant

than two bermudagrass cultivars. Also, Diamond zoysiagrass maintains acceptable TQ

scores under 75% to 81% shade (Qian et al., 1998; Qian and Engelke, 1999). Previous

studies have also indicated that seashore paspalum cultivars are more shade tolerant than

bermudagrass cultivars, „TifSport‟ and TifEagle (Jiang et al., 2004 and 2005). Similar

results were noted in this study as Sea Isle 2000 consistently outperformed Tifway in

shade, however, data collected indicates that Celebration possesses a similar shade

tolerance to Sea Isle 2000. Regardless, both cultivars TQ scores were below 6 by week 8

of shade stress.

Previous reports have indicated Celebration bermudagrass is more shade tolerant

than Tifway bermudagrass (Bunnell et al., 2005c; Baldwin et al., 2008). While plants

have evolved many adaptive mechanisms in order to adapt to natural variations in the

environment, including photosynthesis, these adaptive changes are currently unknown

regarding bermudagrass shade tolerance. A reason for this enhanced shade adaptation

appears to be a morphological advantage exhibited by Celebration. Typically, inhibited

lateral stem growth negatively impacts warm-season turfgrass development when

sunlight is intercepted (Beard, 1997). Also, a shaded cool-season turfgrass, tall fescue

(Festuca arundinacea Schreb.), shifted biomass production from roots to shoots, which

led to thinner and less dense leaf blades compared to full-sunlight (Allard et al., 1991).

151

In this study, under full-sunlight, Celebration clipping yield production was consistently

lower than Tifway, while Celebration lateral spread was greater than Tifway. Similar

trends were noted under shade. Karcher et al. (2005a) reported similar results as

Celebration recovery from divot stress was quicker than Tifway bermudagrass. Clipping

yield and lateral spread data indicates Celebration minimizes vertical shoot growth and

continues energy constituent allocation for continued lateral shoot growth production

under shade. This plastic, morphological adaptation could possibly be due to plant

hormone manipulation, in particular, gibberellic acid (GA), photoreceptor activity

(phytochrome/chromophore), anatomical alterations, or efficient sun-fleck utilization.

All of these possibilities would lead to increased carbon dioxide (CO2) fixation capacity

at reduced light intensities.

Boardman (1977) indicated shade plants can increase solar energy collection

efficiently by altering chloroplast arrangement. Few published reports compare shade-

sensitive and shade-tolerant turfgrass cultivars anatomical development when grown

under shade. Wilkinson and Beard (1975) reported shade-tolerant „Pennlawn‟ red fescue

(Festuca rubra L.) grown under shade developed a thicker cuticle layer, enhanced

vascular support tissue, and maintained a distinct chloroplast structure compared to shade

sensitive „Merion‟ Kentucky bluegrass (Poa pratensis L.). However, Wherley et al.

(2005) noted few anatomical differences between shade-tolerant and shade-sensitive tall

fescue cultivars grown under shade. Future studies investigating the anatomical

development of Celebration may provide clues to its apparent relative shade-tolerance.

152

Efficient conversion of short bursts of solar energy (sun-flecks) into carbohydrate

production supporting lateral stem growth may also enhance Celebration‟s relative shade-

tolerance. The unique anatomical organization of C4 plants typically enhances adaptation

to warm and dry climatic regions because CO2 levels remain elevated near ribulose

bisphosphate carboxylase/oxygenase (Rubisco). However, this unique anatiomical

organization may reduce C4 plants ability to adapt to variable environments, such as low

light, because C4 photosynthesis requires coordinated changes between mesophyll and

bundle sheath tissues (Sage and McKown, 2006). Specifically, C4 plants can not readily

adapt to sunflecks (typically occur in heavily shaded environments) due to distance

between mesophyll CO2 fixation reactions and bundle sheath Calvin cycle metabolites

(Horton and Neufeld, 1998). Future studies determining the importance of sun-fleck

contribution to C4 turfgrass photosynthesis is warranted.

The impact of light quality on turfgrass growth and development remains poorly

understood. In other plant disciplines, spectral shade results in greater individual leaf

area and plant biomass compared to neutral shade (typically used in turfgrass research)

(Stuefer and Huber, 1998). Increased overall above-ground biomass for shade-sensitive

turfgrasses is detrimental due increased tissue removal from mowing. Overall, in this

study, yellow and red shade performed similarly, closely followed by blue shade. Shade

provided by the black cloth consistently resulted in poorest performance of all

turfgrasses.

Compared to blue shade, yellow shade on several occasions produced greater

clipping yield (i.e. plant height), while red shade produced similar clipping yield data for

153

most turfgrasses. Chlorophyll concentrations remained similar between different types of

light, however Diamond grown under blue shade produced 32% and 46% (week 3)

greater chlorophyll than red shade. Similar results have been noted in other studies. In

chrysanthemums (Dendranthema grandiflorum) plants, filtering wavelengths <500 nm

produced tallest plants (Khattak and Pearson, 2006). Poudel et al. (2008) noted grape

(Vitis spp.) genotypes grown under ~600 - 680 nm light had lowest chlorophyll content,

but greatest plant height compared to ~430 - 510 nm light. Similarly, Lee et al. (2007)

determined light with a peak emission of 440 nm produced 54% greater chlorophyll, but

8% less plant dry weight than light with a peak emission of 650 nm for Ashwagandha

(Withania somnifera (L.) Dunal.). In another study, lettuce genotypes (Lactuca Sativa

L.) shoot production under red light was 3.8 units greater than blue light exposure

(Hunter and Burritt, 2004). Kim et al. (2004) reported that chrysanthemums exposed to

650 nm light produced 40% greater plant dry weight than 440 nm light grown plants.

However, chlorophyll concentrations were not impacted by either type of light. McVey

et al. (1969) also reported blue shade resulted in reduced shoot biomass production.

Khattak and Pearson (2006) noted the number of chrysanthemums stomata were greater

under blue shade compared to red shade. This may indicate light with shorter

wavelengths (i.e. blue light) may play a significant role in plant photosynthesis.

154

Conclusion

In summary, this study has demonstrated that both quantity and quality of light

impacts growth and development of various turfgrass species. Also, turfgrass species

growth responses varied under reduced light. Overall, black shade most negatively




Future studies continuing light quality research for other warm-season turfgrass cultivars

needs to be initiated, as well as field studies confirming these greenhouse results. Also,

this study did not take into account the impact of the R:FR ratio, which could potentially

alter results. This study implies different types of shade significantly impact the

performance of warm-season turfgrasses.

155

CHAPTER IX

CREEPING BENTGRASS SEASONAL RESPONSES TO VARIOUS WINTER LIGHT

INTENSITIES

Introduction

Creeping bentgrass (Agrostis stolonifera var. palustris (Huds.)), a C3 plant, has

been widely used as a putting green turfgrass in cooler climate areas and the transition

zone (McCarty et al., 2005). However, due to seasonal temperature variation in the

transition zone, creeping bentgrass putting greens face many stresses and agronomic

challenges year round, including shade. Cool-season turfgrass decline in severe shade is

mainly attributed to increased disease pressure (Beard, 1965; Beard 1969; Vargas and

Beard, 1981), partially because tree water transpiration is greatest at night extending dew

duration (Dudeck and Peacock, 1992; Williams et al., 1996, 1998). Current management

strategies to combat shade stress include raising height of cut (White, 2004; Bunnell et

al., 2005b), reducing nitrogen (N) input (Burton et al., 1959; Bell and Danneberger,

1999b; Goss et al., 2002; Bunnell et al., 2005b;), applying plant growth regulators

(PGRs) (Qian et al., 1998; Qian and Engelke, 1999; Stier and Rogers, 2001; Ervin et al.,

2004; Bunnell et al., 2005b), and watering deeply and infrequently (Dudeck and Peacock,

1992).

Trinexapac-ethyl (TE, Primo Maxx, Syngenta Chem Co., Greensboro, NC)

effectively inhibits gibberellic acid (GA) production (Adams et al., 1992) late in the

mevalonic acid pathway suppressing shoot vertical growth. In Kentucky bluegrass (Poa

156

pratensis L.) cultivars, TE (0.048 kg a.i. ha-1

) reduced GA1 49% and increased GA20

146% when grown in 87% shade (Tan and Qian, 2003). Due to GA disruption, TE

enhances warm-season and cool-season turfgrass response when light interception is

interrupted.

„Penncross‟ creeping bentgrass grown in 80% shade treated with multiple TE

applications at 0.042 and 0.070 kg a.i. ha-1

increased fructose concentration ~39% with

minimal effects on other carbohydrate constituents (Goss et al., 2002). Similarly, Steinke

and Stier (2003) noted monthly and bimonthly TE applications enhanced Penncross

creeping bentgrass TQ and chlorophyll concentration in 80% shade. It appears consistent

TE applications is an effective management strategy to reduce shade damage. However,

Gardner and Wherley (2005) noted a TQ decline for tall fescue (Festuca arundinacea

Schreb. „Plantation‟), rough bluegrass (Poa trivialis L.), and sheep fescue (Festuca ovina

L.) and turfgrass density decline in tall fescue and rough bluegrass grown under Acer

saccharinum L. and Platanus occidentalis L. trees (91% light reduction) four to six

weeks after TE (0.29 kg a.i. ha-1

) applications.

While morning shade is perceived more detrimental than afternoon shade for

warm- and cool-season turfgrass growth, few experiments have investigated this

observation. Bell and Danneberger (1999a) noted shade duration was more detrimental

than morning or afternoon shade for Penncross creeping bentgrass. However, a warm-

season species, „TifEagle‟ bermudagrass (Cynodon dactylon (L.) Pers. X C.

transvaalensis), declined more readily in the absence of afternoon solar irradiance

(Bunnell et al., 2005a).

157

In the transition zone, creeping bentgrass putting greens often experience summer

decline due to a combination of stresses, which include elevated soil CO2 levels (Bunnell

et al., 2002; Rodriguez et al., 2005), high soil temperatures (Xu and Huang, 2000; Xu and

Huang, 2001), and increased day and night temperatures (Huang and Gao, 2000; Fu and

Huang, 2003). Management practices to combat these stresses are well documented

(Dernoedon, 2000; Feng et al., 2002; Liu and Huang, 2003; Bunnell et al., 2004; Guertal

et al., 2005). Winter shade is potentially very damaging due to shorter photoperiods,

reduced light intensities, solar elevation angles, and extended frost accumulation.

However, winter shade impacts on creeping bentgrass putting greens and management

recommendations to minimize winter shade stress have yet to be investigated. Also,

winter shade effects on spring and summer performance are lacking. Therefore, research

objectives of this study included evaluating winter shade impacts on the performance of

„L93‟ creeping bentgrass, responses of L93 creeping bentgrass under morning or

afternoon shade, effects of winter month shade on spring and summer performance, and

TE as a management tool to reduce winter shade stress.


This research was conducted at the Turfgrass Research Center, Clemson

University, Clemson, SC on L93 creeping bentgrass field research plots established in

August, 2002 with soil profile constructed to approximate United States Golf Association

(USGA) recommendations (USGA, 1993). Shade treatments were initiated 1 December

2004 and terminated 28 February 2005 and repeated the subsequent winter. Data

158

collection continued through July each year to determine any deleterious effects that

continuous, morning, or afternoon winter shade had on spring and summer bentgrass

performance. Light treatments consisted of control (no shade), 55%, and 95% (Table 1)

light reductions using a neutral density, polyfiber black shade cloth (Glenn Harp and

Sons, Inc., Tucker, GA) supported by polyvinyl chloride (PVC) 183 cm in length and 152

cm in width with 2.54 cm diameter PVC pipes. Shade structures were placed 15 cm

above the bentgrass surface to reduce early morning and late afternoon sunlight

encroachment, yet maintain adequate wind movement. For morning shade, tents were

placed on the bentgrass surface at sunrise and removed at solar noon. For afternoon

shade, tents were placed on the bentgrass surface at solar noon and removed at sunset.

For full-day shade, tents were placed on the bentgrass surface at sunrise and removed at

sunset. Regardless of shade treatment, all tents were removed nightly.

Trinexapac-ethyl was applied at 0.02 kg ha-1

using the emulsifiable concentrate

(11.3% a.i.) using a CO2–pressurized backpack sprayer beginning on 1 December and

every two weeks through 31 July each year. The bentgrass green was mowed at 3.2 mm

height two to four times weekly during winter depending on weather conditions with

clippings removed. During spring, summer, and fall, mowing (3.2 mm) occurred six to

seven times weekly. A combination of 10N-1.3P-4.2K and 5N-0P-5.8K liquid fertilizers

(Progressive Turf, LLC., Ball Ground, GA) were applied early January 2005 and 2006 at

a rate of 4.9 kg N ha-1

. In spring, a rate of 9.7 kg N ha-1

was applied every two weeks

using Progressive Turf liquid fertilizer, while in summer, same liquid fertilizer (10-1.3P-

4.2K and 5-0P-5.8K) was applied at a rate of 4.9 kg N ha-1

every two weeks. In fall, N

159

was applied every two weeks at a rate of 9.7 kg ha-1

using liquid fertilizers (10N-1.3P-

4.2K and 5N-0P-5.8K). Hollow tine aerification (1.3 cm diam. tines 10 cm in length with

5.0 cm spacing) occurred twice in the spring and once in the fall. Following cultivation,

a rate of 24.4 kg N ha-1

using 18N-1.3P-14.9K greens grade granular fertilizer

(Anderson‟s, Maumee, OH) was applied. Disease occurrence in winter was minimal,

therefore no fungicides were applied. In summer, chlorothalonil (Daconil) (11.8 L ha-1

),

azoxystrobin (Heritage) (48 kg a.i. ha-1

), and mefonoxam (Subdue MAXX) (6.4 L ha-1

)

were applied as needed for dollar spot (Sclerotinia homoeocarpa F.T. Bennet), pythium

(Pythium spp.), and brown patch (Rhizoctonia solani Kuhn.) management. The bentgrass

green did not receive any topdressing, except following aerifications.

Data collection

Data collected included microenvironment conditions, visual turfgrass quality

(TQ), clipping yield, shoot chlorophyll concentration, total root biomass, and root total

non-structural carbohydrates (TNC).

Microenvironment parameters included surface and soil temperature, wind

movement, and light quality and quantity. Surface and soil temperature was recorded

four times weekly during winter months at solar noon for one full-sun treatment, under

one 55% and one 95% shade cloth using an indoor/outdoor thermometer (model #1455

and model #9840, Taylor, Oakbrook, IL). Sensors for surface temperature were placed

on the surface, while soil temperatures were recorded at a 7.6 cm depth. Wind movement

was recorded twice on days with a consistent breeze using an anemometer (model #CS-

800, Clark Solutions, Hudson, MA). Light quality was measured on a clear, cloudless

160

day at solar noon using a spectroradiameter (Model LI-1800; LiCor, Inc., Lincoln, NE),

while photon flux density ( mol m-2

s-1

) was recorded four times weekly during winter

months at solar noon for one full-sun treatment, under one 55% and one 95% shade cloth

using a quantum radiometer (Model LI-250, LiCor, Lincoln, NE).

Visual TQ ratings were measured monthly based on color, density, texture, and

uniformity of the L93 creeping bentgrass surface. Quality was visually evaluated from 1

to 9, 1 = brown, dead turf, 6 = minimal acceptable turf, 9 = ideal green, healthy turf.


) was collected mid-January, late-February, and mid-May for

both years. Shoot tissue was collected using a walk behind greens mower

(Greenmaster® 800, The Toro Company, Bloomington, MN) following three days of

growth. Clippings were oven dried at 80oC for 48 hr and weighed to quantify shoot

production.


) was determined on same dates as clipping yield. Fresh

clippings were collected (as described above) from each plot and immediately placed in a

plastic bag inside a covered bucket to prevent sunlight degradation. Clippings were

weighed (0.1g) and placed in a glass test tube (1.0 cm in width and 14.8 cm in length)

with 10 mL of dimethyl sulfoxide (DMSO), which eliminates shoot tissue grinding to

extract chlorophyll (Hiscox and Israelstam, 1979). Samples were incubated in 65 oC


Upon completion, samples were passed through filter paper (Whatman 41, Whatman,

England) and remaining extract (2 mL) transferred into cuvettes. Absorbance values

were recorded at 663 nm and 645 nm wavelengths using a spectrophotometer (GenesysTM

161

20, ThermoSpectronic, Rochester, NY). Blanks were initially run and also after every

sixth sample. The following formula was used to calculate total shoot chlorophyll: (mg

g-1

) = (8.02 * D663 + 20.2 * D645) * 0.1 (Arnon, 1949).

Roots were extracted from the soil using a cylinder core sampler (7.5 cm in diam.

by 30 cm deep) 15 January and 28 February for both years to determine total root

biomass. One plug was randomly sampled from each plot and re-filled with 85:15 sand:

peat. For all future parameters, the old plug site was ignored. Once all soil was

completely removed from each soil plug using tap water, roots were clipped from shoot

tissue base and placed in an oven (80.0 oC) for 48 hr, then weighed.

Root TNC (mg g-1

) was collected end of February for both years. Root tissue was




oC for two wks to cease all




mm. Rehydrated samples were placed in boiling water for 1 hr, cooled for 1 hr and



(Sigma A-7255, 23,000 units g-1

) were added to solution. Samples were placed in water

bath (40 – 45oC) for three days and vortexed three times daily. TNC analysis was

analyzed using Nelson‟s Assay (1944), which determines glucose and fructose in plant

tissue (Nelson, 1944; Somogyi, 1945). A 25 L of aliquot was removed and two

162

reagents (copper and arsenomolybdate) were added to the solution. Absorbance values

were measured at 520 nm using a spectrophotometer.

Data Analysis

Treatment factors were arranged in a split-block design with four replications.

Treatment effects were evaluated using analysis of variance within SAS (version 9.1,

SAS Institute, Cary, NC). No treatment by TE interactions occurred for any parameters;

therefore, marginal means for light treatments and TE were examined separately. For TQ

scores, year by treatment interactions occurred for January, February, and March,

therefore yearly results are presented separately. For chlorophyll and clipping yield, year

by treatment interactions occurred for January, therefore yearly results are presented

separately. All other parameters showed no significant treatment by year interactions,

therefore, yearly data were pooled. Means separation was performed using Fisher‟s

protected least significant difference (LSD) test with = 0.05.

Results

Microenvironment

Shade significantly altered the microenvironment for each treatment (Table 9.1).

The 55% and 95% shade cloths reduced light intensity 58% and 96% compared to full-

sunlight. Within each month, 95% full day shade significantly reduced surface

temperatures ~57% compared to full-sunlight. In December and February, 95% full day

163

Table 9.1. Winter surface and soil temperatures (oC) and percent light reduction

recorded at solar noon four times weekly from 1 December to 28 February in year I and

II.

Surface and soil temperature (oC)

Light intensity

( mol m-2

s-1

)

Treatment December January February December to

February

Surface Soil Surface Soil Surface Soil

FS

† 17.3 5.7 20.8 8.4 22.8 8.5 338.2

55FD 13.2 4.3 16.7 7.3 18.0 6.9 143.2

95FD 10.8 3.9 14.0 6.8 14.1 6.1 12.6

LSD 2.25

‡ 1.32 2.54 1.65 3.17 1.80 29.07

†Abbreviations: FS=full-sunlight, 55FD=55% full day shade, 95FD=95% full day shade.

‡Values within a column followed by the same letter are not significantly different at P≤0.05

by protected LSD.

shade treatment soil temperatures were ~43% lower than full-sunlight. Also, coldest

surface and soil temperatures occurred in December, followed by a gradual warming

trend from January to February. Light quality and wind speed were not affected by shade

cloths and structures (data not shown).

Turfgrass Quality

One month following shade treatment initiation, significant differences were

noted between treatments (Table 9.2). In December, full-day 95% shade produced

highest TQ (7.4) compared to all other treatments, however, this response was transient in

year I. In year I, by January (4.9) and February (4.2), full-day 95% shade showed lowest

TQ scores compared to all other treatments. No differences were detected between

164

Table 9.2. Turfgrass quality of 'L93' creeping bentgrass in December, January,

and February in response to full-sunlight and 55% and 95% morning,

afternoon, and full-day winter shade (December to February, 2004 to 2006) and


) applications every two weeks from 1 December to

31 July, 2004 to 2006.

-----------------Turfgrass Quality†-------------

Light Duration

Trinexapac-

ethyl (TE) December January February

Year

1

Year

II

Year

1

Year

II

Full-

sunlight

-- 5.7 6.8 5.2 5.5 5.1

55%

shade Morning -- 6.3 6.7 5.5 6.2 5.3

Afternoon -- 6.5 7.3 5.7 6.6 5.4

Full-day -- 6.7 6.8 6.4 6.0 6.3

95%

shade Morning -- 6.7 6.7 6.1 6.0 6.1

Afternoon -- 6.8 6.8 6.1 6.6 5.9

Full-day -- 7.4 4.9 6.8 4.2 6.3

---------------------------LSD---------------------

0.40‡ 0.57 0.56 0.55 0.59

TE 6.6 6.5 5.9 5.5 5.5

No TE 6.5 6.6 6.1 6.2 6.0

---------------------------LSD---------------------

NS NS NS 0.29‡ 0.31


acceptable turfgrass, 9=healthy/green turfgrass. ‡Values within a column followed by the same letter are not significantly


LSD, least significant difference, NS = not significant.

morning and afternoon shade in December. Afternoon shade (55%) showed a 0.6 unit

TQ increase compared to morning shade (55%), however, this difference was not

detected in January, 2006 or in February for either year. Differences were not detected

between full-day and diurnal 55% shade in January, 2005, however afternoon 55% shade

165

increased TQ 0.6 units compared to full-day 55% shade. In January, 2005, morning and

afternoon shade (95%) had a ~1.9 unit TQ increase compared to full-day 95% shade.

Similarly, in February, 2006, full-day 95% shade reduced TQ by ~2.1 units compared to

morning and afternoon 95% shade.

Unlike year I, in 2006, full-day 95% shade remained above the acceptable TQ

threshold of 6 through January and February (Table 9.2). No differences were detected

between morning or afternoon shade for either shade intensity. However, full-day 55%

shade increased TQ ~0.8 and ~1.0 units compared to morning or afternoon 55% shade.

When grown under full-day 95% shade, bentgrass TQ increased 0.7 units compared to

95% morning or afternoon shade.

Trinexapac-ethyl applications every 2 wks did not impact TQ scores in December

or January (Table 9.2). However, TE-treated plots in February, 2005 and 2006 showed a

0.7 and 0.5 unit TQ decrease, respectively, compared to non TE-treated plots.

In March, 2005, 95% afternoon shade increased TQ 0.8 units compared to

morning 95% shade, however, no morning or afternoon TQ variations were noted under

55% shade (Table 9.3). Regardless, full-day 95% shade produced lowest TQ (4.3)

compared to other treatments. Minimal winter sunlight negatively impacted spring or

summer TQ ratings. By April, regardless of winter shading, all plots had acceptable TQ.

Trinexapac-ethyl increased TQ by 0.6 and 0.2 units in May and June, respectively,

compared to non TE-treated plots.

166

Table 9.3. Turfgrass quality of 'L93' creeping bentgrass in spring and summer in

response to full-sunlight and 55% and 95% morning, afternoon, and full-day

winter shade (December to February, 2004 to 2006) and trinexapac-ethyl (0.02

kg ha-1

) applications every two weeks from 1 December to 31 July, 2004 to 2006.

-------------------Turfgrass Quality†-----------

Light Duration

Trinexapac-

ethyl (TE) March April May June July

Year

1

Year

II

Full-

sunlight

-- 5.3 5.5 6.7 7.1 7.5 6.6

55%

shade Morning -- 5.7 6.0 6.8 7.1 7.6 6.4

Afternoon -- 5.8 6.2 7.1 7.5 7.8 6.2

Full-day -- 5.5 6.4 6.8 7.4 7.5 6.5

95%

shade Morning -- 5.3 6.0 6.7 7.2 7.4 6.2

Afternoon -- 6.1 6.1 7.0 7.2 7.4 6.6

Full-day -- 4.3 6.3 6.9 6.9 7.5 6.6

-----------------------------LSD----------------------- 0.64

‡ NS NS 0.40 0.15 0.27

TE 5.5 5.9 6.9 7.5 7.6 6.4

No TE 5.5 6.2 6.7 6.9 7.4 6.4

-----------------------------LSD----------------------- NS 0.29

‡ NS 0.21 0.08 NS


acceptable turfgrass, 9=healthy/green turfgrass. ‡Values within a column followed by the same letter are not significantly different at

P≤0.05 by protected LSD. LSD, least significant difference, NS

= not significant.

Chlorophyll

In January, 2005, 55% afternoon shade produced greatest chlorophyll

concentration (3.0 mg g-1

), however, in year II, 95% full-day shade produced greatest

chlorophyll concentration (2.2 mg g-1

) (Table 9.4). No differences were detected

167

Table 9.4. Chlorophyll concentration (mg g-1

) of 'L93' creeping bentgrass in

January, February, and May in response to full-sunlight and 55% and 95%

morning, afternoon, and full-day winter shade (December to February, 2004 to

2006) and trinexapac-ethyl (0.02 kg ha-1

) applications every two weeks from 1

December to 31 July, 2004 to 2006.

-----------Chlorophyll (mg g-1

)-------

Light Duration

Trinexapac-ethyl

(TE) January February May

Year

1

Year

II

Full-

sunlight

-- 2.5 1.5 2.0 2.4

55% shade Morning -- 2.4 1.6 2.1 2.4

Afternoon -- 3.0 1.6 2.1 2.5

Full-day -- 2.7 1.7 2.2 2.3

95% shade Morning -- 2.5 1.8 2.2 2.4

Afternoon -- 2.6 1.8 2.3 2.4

Full-day -- 2.5 2.2 2.5 2.5

---------------------LSD------------------- 0.64

† 0.20 0.16 NS

TE 2.5 1.7 2.1 2.5

No TE 2.6 1.8 2.2 2.3

---------------------LSD------------------- NS NS 0.08

† NS

† Values within a column followed by the same letter are not significantly different


LSD, least significant difference, NS = not significant.

between 95% shade treatments in year I, while morning or afternoon shade did not

impact chlorophyll concentration in January, 2006. In February, full-day 95% shade

enhanced chlorophyll 25%, ~17%, and ~12% compared to full-sunlight, 55% shade

treatments, and 95% shade treatments. Meanwhile, morning or afternoon shade did not

influence chlorophyll concentrations. Also, chlorophyll differences were not detected in

168

May. Trinexapac-ethyl had minimal impacts on winter and spring chlorophyll

concentrations. In February, non TE-treated bentgrass minimally increased chlorophyll

concentration 5% compared to TE-treated plots.

Clipping Yield

Full-day 95% shade increased shoot growth 1.5 units compared to full-sunlight in

January, 2005 (Table 9.5). Also, morning shade (55%) decreased shoot growth 78%

compared to afternoon shade (55%). Clipping yield differences were not detected in

January, 2006. In February, clipping yield production increased 47% for bentgrass when

grown under 95% full-day shade compared to full-sunlight. By May, no shoot biomass

variations were noted. Trinexapac-ethyl reduced shoot growth ~38%, 79%, and 51% in

January (2005 and 2006), February, and May, respectively compared to non TE-treated

plots.

Root Biomass and total nonstructural carbohydrates

In February, 2006, shade treatments, regardless of intensity or duration, had ~49%

reduction in root biomass compared to full-sunlight (Table 9.6). Morning shade (55%)

reduced root TNC 19% compared to afternoon shade, however, under 95% shade, a 20%

root TNC increase was noted for morning shade compared to afternoon shade. Also, full-

sunlight produced 27%, 32%, and 25% greater root TNC compared to full-day 55%

shade, 95% afternoon shade, and 95% full-day shade, respectively. Trinexapac-ethyl did

not impact root biomass or root TNC in the winter.

169


) of 'L93' creeping bentgrass in January, February,

and May in response to full-sunlight and 55% and 95% morning, afternoon, and

full-day winter shade (December to February, 2004 to 2006) and trinexapac-ethyl

(0.02 kg ha-1

) applications every two weeks from 1 December to 31 July, 2005 to

2006.

----------Clipping Yield (g m

-2)------------

Light Duration

Trinexapac-

ethyl (TE) January February May

Year

1

Year

II

Full-

sunlight

-- 1.09 0.49 0.36 0.47

55% shade Morning -- 1.73 0.47 0.44 0.42

Afternoon -- 1.98 0.47 0.34 0.46

Full-day -- 1.89 0.43 0.33 0.45

95% shade Morning -- 1.37 0.52 0.35 0.43

Afternoon -- 2.44 0.47 0.39 0.46

Full-day -- 2.72 0.38 0.53 0.40

------------------------LSD----------------------

1.022† NS 0.156 NS

TE 1.56 0.39 0.28 0.35

No TE 2.23 0.52 0.50 0.53

------------------------LSD----------------------

0.546† 0.104 0.083 0.043


P≤0.05 by protected LSD. LSD, least significant difference, NS = not

significant.

170

Table 9.6. Total root biomass (g m-2

) and root total nonstructural carbohydrates

(mg g-1

) of 'L93' creeping bentgrass in January and February in response to full-

sunlight and 55% and 95% morning, afternoon, and full-day winter shade and


) applications every two weeks from 1 December to

31 July, 2005 to 2006.

Root Biomass

(g m-2

)

Root TNC

(mg g-1

)

Light Duration

Trinexapac-

ethyl (TE) January February

February

Full-

sunlight

-- 0.79 0.89

52.6

55%

shade Morning -- 0.64 0.64

46.3

Afternoon -- 0.81 0.61

55.2

Full-day -- 0.76 0.66

41.5

95%

shade Morning -- 0.71 0.58

47.9

Afternoon -- 0.86 0.60

39.9

Full-day -- 0.61 0.51

41.9

--------------------------LSD-----------------------

NS 0.229† 6.79

TE 0.76 0.62

45.5

No TE 0.72 0.66

47.5

--------------------------LSD-----------------------

NS NS NS †Values within a column followed by the same letter are not significantly different at

P≤0.05 by protected LSD. LSD, least significant difference, NS = not significant.

Discussion

Spring is a period of accelerated growth and carbohydrate accumulation of

creeping bentgrass in the transition zone. Therefore, winter shade, which is largely

ignored in the turfgrass literature, was evaluated to determine if limiting light availability

during winter months would inhibit spring and subsequent summer performance. To the

171

author‟s knowledge, this if the first research project initiated to specifically investigate

the impact of winter shade on creeping bentgrass putting greens.

Results indicate moderate to heavy winter shade may not be a limiting growth

factor for creeping bentgrass putting greens in the transition zone. Contributing to

bentgrass shade tolerance is its low requirement for sunlight. Typically, C3 plants are

able to maintain an appropriate photosynthesis:respiration ratio, where photosynthesis

exceeds respiration, compared to C4 plants in low light environments (Wahid and Rasul,

2005), possibly due to distance between mesophyll and bundle sheath tissues (i.e.

anatomical organization) (Sage and McKown, 2006) or efficient sunfleck utilization

(Horton and Neufeld, 1998). Previous research indicates bentgrass performs well under

moderate shade stress. Goss et al. (2002) stated bentgrass showed minimal deleterious

effects under 60% shade, while 80% shade inhibited bentgrass growth and development.

Bell and Danneberger (1999a) also indicated Penncross creeping bentgrass maintained

acceptable color, density, and tissue mass when grown under 69% shade. Reid (1933)

indicated bentgrass grown under heavy shade had comparable light green color compared

to controls (full-sunlight), however, root growth was restricted. These studies were

conducted to coincide with spring season leaf growth and/or fall season leaf drop.

In this study, following three months of winter shade, regardless of intensity or

duration, shade treatments consistently showed greater TQ scores and chlorophyll

concentrations compared to full-sunlight plots. Evergreen plants photosynthetic rates

decline when temperatures cool, however, chlorophyll continues its light absorbing

properties (Verhoeven et al., 2005). Therefore, photoinhibition will occur unless the

172

xanthophyll cycle and/or antioxidant leaf enzymes are employed by the plant to minimize

the impact of excessive light accumulation (Deming-Adams and Adams, 1996). In this

study, it appears increasing shade intensity served as a photo-protective role under

apparent high light stress, thereby minimizing excess light accumulation in the light-

harvesting complexes, which ultimately produces reactive oxygen species. Limited

research examining the role of xanthophyll pigments in turfgrass exists. Bell and

Danneberger (1999a) noted in a field study that bentgrass decreased violaxanthin

concentration with increasing shade stress, while other pigment concentrations remained

constant. McElroy et al. (2006), in a greenhouse study, reported carotenoid (zeaxanthin,

antheraxanthin, violaxanthin, neo-xanthin, epoxy-lutein, and -carotene) concentrations

decreased as low light intensity duration increased. Both of these studies examined

carotenoid concentrations during favorable growing temperatures for bentgrass. Future

studies investigating xanthophyll activity of cool-season turfgrasses under winter shade is

warranted to further understand the relationship between winter shade stress and

bentgrass performance. Differences between 95% full-day shade in year I and II remains

unknown. Monthly maximum and minimum air temperatures and precipitation were

examined. Temperature and precipitation differences did not occur over this two-year

field study (data not shown), therefore, it appears this yearly fluctuation is independent of

temperature and/or moisture availability.

While TE typically enhances cool-season turfgrass in shade (Goss et al., 2002;

Steinke and Stier, 2003; Tegg and Lane, 2004), this study indicates TE applications every

two weeks during winter negatively impacted bentgrass growth and color. Bentgrass

173

growth slowed due to cool winter temperatures, therefore, applying TE, a gibberellin

inhibiting PGR which slows growth, further reduced growth and discolored bentgrass.

Other studies on warm-season turfgrasses have noted surface discoloration and density

decrease if TE is applied during periods below an optimal growth temperature range

(Johnson, 1994; Fagerness and Yelverton, 2000; McCullough et al., 2006; McCullough et

al., 2007). Also, Gardner and Wherley (2005) reported TE applied every 6 wks

decreased visual TQ and density of cool-season turfgrasses under shade stress. Greater

intervals between winter TE applications or reduced rates may have been more

beneficial. Beasley et al. (2007) noted TE uptake was greatest when temperature were

warm, however, dissipation rate increased compared to cooler temperatures. Therefore,

during cool winter months, as TE efficacy is greatest, applying TE in two week intervals

in unnecessary and caused bentgrass discoloration. Weekly winter temperature

fluctuations in the transition zone are common, therefore, prudent use of TE to

temporarily slow shoot growth during winter when temperatures are forecasted to be

above average should further enhance bentgrass performance in shade by minimizing

excessive shoot growth. When temperatures are below average for an extended period,

TE use should be applied with caution. Once shade tents were removed and temperatures

were consistently warm, TE enhanced bentgrass performance in spring and summer.

Moderate winter shade seemed beneficial for parameters measured in this study;

however, long-term effects of 95% shade through spring and into summer may decrease

bentgrass visual quality. While TQ and shoot chlorophyll concentrations increased under

95% shade in February, 2006, root mass and root TNC declined compared to full-sunlight

174

in February. This indicates bentgrass re-allocated energy constituents and carbohydrate

reserves to shoot tissue to maintain winter green color and continued winter growth,

instead of conserving carbohydrates. This strategy would presumably be detrimental

(i.e., carbohydrate depletion) for sustaining a high quality putting green surface during

summer stress if 95% shade continued through the spring. However, Beard and Daniel

(1966) noted temperature reductions enhanced „Old Orchard‟ creeping bentgrass root

activity. Thus, partial spring and summer shade, which reduces surface and soil

temperatures, may improve creeping bentgrass survival in the hot, humid transition zone

by initiating new summer root growth, as long as a prudent disease control program is

initiated.

Trinexapac-ethyl did not impact root biomass. Fagerness and Yelverton (2000)

also reported year-round TE applications did not enhance bentgrass root biomass.

Similarly, McCullough et al. (2007) reported no differences in non TE-treated compared

to TE-treated bentgrass root growth following late-spring and summer TE applications.

While TE did not increase root TNC in this study, Ervin and Zhang (2007) reported

increases in bentgrass leaf carbohydrate content following sequential TE applications in a

greenhouse study. Goss et al. (2002) reported TE-treated creeping bentgrass increased

carbohydrate content under 80% shade stress compared to non TE-treated creeping

bentgrass. Also, Goss et al. (2002) observed significant increases in shoot carbohydrate

content compared to root carbohydrate content of bentgrass when grown under 80%

shade. In our study, sampling shoot tissue TNC may have been more appropriate than

root TNC regarding shade stress.

175

Overall, morning or afternoon shade minimally impacted parameters measured.

Results agree with Bell and Danneberger (1999a) which stated shade duration rather than

diurnal shade was more detrimental to Penncross creeping bentgrass growth under 80%

or 100% shade. However, in this study, 55% and 95% diurnal shade differently impacted

parameters measured. For example, 55% morning shade reduced root TNC, while 95%

morning shade enhanced root TNC compared to afternoon shade. Bunnell et al. (2005)

noted afternoon shade decreased root carbohydrate content of TifEagle bermudagrass

compared to morning shade. However, Bell and Danneberger (1999) did not detect any

bentgrass carbohydrate content variation in response to diurnal shade. It appears time of

shade may be more critical for bermudagrass putting greens, rather than cool-season

putting greens. Future research of other turfgrass species and cultivars response to

morning or afternoon shade would prove beneficial.

Conclusion

In summary, intensity of shade enhanced bentgrass growth, while duration of

winter shade had minimal impacts during winter. Regardless of winter stress, all plots

fully recovered by early spring as TQ scores were above the acceptable threshold of 6.

Future studies should investigate bentgrass performance with continued moderate shade

stress throughout spring and summer. Also, other bentgrass cultivars, as well as other

cool-season turfgrass species winter shade performance should be evaluated to determine

if a reduced light environment inhibits growth during winter months.

176

CHAPTER X

VARIOUS WINTER TRAFFIC IMPACTS ON A „L93‟ CREEPING BENTGRASS

PUTTING GREEN

Introduction

In the transition zone, creeping bentgrass is desirable due to year-round green

color, ball roll, and overall playability. However, this turfgrass presents many challenges

throughout summer as well as winter seasons. During summer months, temperatures

exceeding 30oC result in shallow roots (Beard and Daniel, 1965), reduced carbohydrate

reserves (Huang and Gao, 2000), and increased disease susceptibility (Huang, 2001).

Management techniques to understand and possibly alleviate summer stress have been

documented (Guertal et al., 2005; Rodriguez et al., 2005; Bunnell et al., 2004).

Furthermore, winter temperature fluctuations within the transition zone present unique

challenges in bentgrass management. Superintendent daily dilemmas during winter

months in the transition zone include when to allow course set-up and play to initiate

when temperatures approach 0oC. Often, tee times are delayed or cancelled resulting in

lost revenues and tension between players and superintendents.

Water vapor condensation settling on turfgrass foliage becomes frost when

temperatures approach 0oC. Winter traffic, whether by foot, equipment, or animal,

during periods of frost typically cause damage, leaving turfgrass discolored. At colder

temperatures, processes such as photosynthesis and respiration are inhibited as cells enter

a gelatinous consistency resulting in possible membrane puncture (Fry and Huang, 2004).

177

Frost accumulation is also detrimental because ice crystals damage the protoplasm

(Beard, 1973). Plants maintaining an unsaturated fatty acid (double bond between carbon

atoms) composition enhances membrane fluidity (Cyril et al., 2002), thereby reducing

foliage damage.

Several management techniques are available to minimize winter injury. During

cool winter months at the Old Course in St. Andrews, golfers are required to use artificial

mats when hitting shots from fairways to minimize divot damage and subsequent slow

spring recovery (Hartwiger, 2005). Using insulated (straw or curled wood mat)

protective covers increase soil temperatures by 4.3oC and reduce seasonal soil

temperature variation, enhancing turfgrass winter survival (Dionne et al., 1999). Lightly

syringing greens prior to daily traffic and restricting golf cart access on fairways, tees,

and greens until temperatures exceed 0oC can also minimize winter-kill or damage

(White, 1984). Application of abscisic acid (ABA) has been shown to enhance freezing

tolerance (Gusta et al., 1996), while a proper fertility program can minimize winter injury

(Webster and Ebdon, 2005).

Numerous studies have been conducted to determine the diversity of turfgrass

freezing stress tolerance (Gusta et al., 1980; Rajashekar et al., 1983; Ebdon et al., 2002;)

and to determine turfgrass survival with or without snow and ice cover removal

(Tompkins et al., 2000; Tompkins et al., 2004; Valverde and Minner, 2007;). All of these

studies were performed in northern United States of America climates and to date,

research has not been reported attempting to quantify the effects of winter traffic injury

on bentgrass grown in the transition zone. Since light to heavy frost occurs on golf

178

courses in temperate climatic regions, superintendents must decide what time and type of

traffic are allowed on their golf courses, while minimizing turfgrass damage and meeting

player satisfaction. The main objective of this study was to access variable traffic

impacts to a creeping bentgrass putting green during winter months and determine

residual effects in spring and summer including 1) comparing 0700 and 0900 traffic

impacts to winter turfgrass quality; 2) comparing foot and walk behind mower traffic

impacts to turfgrass quality; and 3) investigating winter traffic residual effects on spring

and summer turfgrass performance.


This 2-year research project was conducted at Clemson University, Clemson, SC

from 1 December 2005 and 2006 to 1 August 2006 and 2007 on „L93‟ creeping bentgrass

field research plots established in 2002 with soil profile construction approximate to

USGA (United States Golf Association) recommendations (USGA, 1993). Although

simulated traffic treatments were terminated on 1 March 2006 and 2007, data collection

continued through spring and summer to evaluate any residual effects from winter traffic.

Treatments consisted of no traffic (control), foot traffic at 0700 (F7) and 0900 (F9), and

walk behind mower traffic (rolling) at 0700 (R7) and 0900 (R9). Traffic treatments were

applied at 0700 and 0900 when surface temperatures were below 0oC at 0700. Foot

traffic included ~75 steps within each plot using size 10 SP-4 Saddle Nike golf shoes

(soft-spiked sole) which ensured complete coverage of the plot. The majority of traffic

applications for each year were made by a person weighing 75 kg. A Toro®

179

Greensmaster® 800 walk behind greens mower (Greenmaster® 800, The Toro Company,

Bloomington, MN) weighing 92 kg with a 46 cm roller was used to simulate rolling

traffic. One pass was made per plot. Plot dimensions were 46 cm in width by 120 cm in

length, similar width of the mower ensuring complete coverage of the plot. Therefore,

regardless of traffic type, the entire plot area was trafficked. Plots were always rolled and

not mowed when surface temperatures were below 0oC. Mowing occurred over the entire

plot area when surface temperatures were above 7.2oC on non-treatment days.

Depending on air temperature, the bentgrass green was mowed at 3.2 mm three

times weekly during winter months. In early January each year, a combination of 10N-

1.3P-4.2K and 5N-0P-5.8K liquid fertilizers (Progressive Turf, LLC., Ball Ground, GA)

was applied with nitrogen (N) at 4.9 kg ha-1

. Disease occurrence was minimal during the

study period, therefore, no fungicides were applied. Beginning in March and continuing

through August, mowing occurred six to seven times weekly at 3.2 mm. Nitrogen was

provided every 2-weeks at a rate of 9.7 kg ha-1

using Progressive Turf liquid fertilizers

from 15 March to 31 May 2006 and 2007. Following hollow tine aerification (1.3 cm

diam. tines 10 cm in length with 5.0 cm spacing) in spring 2006 and 2007, N was applied

at a rate of 24.4 kg ha-1

using 18N-1.3P-14.9K greens grade granular fertilizer

(Anderson‟s, Maumee, OH). Chlorothalonil (11.8 L ha-1

), Azoxystrobin (48.8 kg ha-1

),

and Mefonoxam (6.4 L ha-1

) were applied as needed to prevent dollar spot (Sclerotinia

homoeocarpa F.T. Bennet), pythium (Pythium spp.), and brown patch (Rhizoctonia

solani Kuhn.) occurrence, respectively.

180

Data Collection

Collected data included surface and soil temperatures (7.6 cm depth) (model

#9840, Taylor, Oakbrook, IL), visual TQ, clipping yield, chlorophyll concentration, root

TNC, bulk density, and water infiltration rates. Surface (model #1455, Taylor,

Oakbrook, IL) and soil (7.6 cm depth) temperatures were recorded after each traffic

application (24 dates) during winter months at 0700, 0900, and solar noon.

Turfgrass quality ratings were recorded after each treatment application (24 rating

dates for both years) based on color, density, texture, and uniformity of the bentgrass

surface. Turfgrass quality scores were also recorded weekly and averaged per month

from March to August, 2006 and 2007. Quality was visually evaluated from 1 to 9, 1 =

brown, dead turfgrass, 6 = minimal acceptable turfgrass, 9 = ideal green, healthy

turfgrass.

Clipping yields (g m-2

) were collected following 8, 16, and 24 traffic applications,

mid-May, and mid-August for both years. Shoots were harvested with a Toro® walk

behind greens mower. For winter collection, the bentgrass green was not mowed for

three days to ensure adequate tissue sample due to slow shoot growth of bentgrass during

the winter. However, for spring and summer collection, the bentgrass green was not

mowed for one day prior to clipping yield collection. After collection, shoots were dried

in an 80oC oven for 48-hours to ensure complete tissue dehydration, then weighed

(McCullough et al., 2006).


) was measured following 8, 16, and 24 traffic

applications, mid-May, and mid-August for both years. Fresh clippings were collected

181

from each plot using a Toro® walk behind greens mower following three days of growth

and immediately placed in a plastic bag inside a covered bucket to prevent sunlight

degradation. Clippings were weighed (0.1g) and placed in a glass test tube (1.0 cm in

width and 14.8 cm in length) with 10 mL of dimethyl sulfoxide (DSMO) (Hiscox and

Israelstam, 1979). Samples were incubated in 65 oC water on a hot plate (PC-600,

Corning, Corning, NY) for 1.5-hour and continuously shaken. Upon completion,

remaining extract (2 mL) was transferred into cuvettes. Absorbance values were

recorded at 663 nm and 645 nm wavelengths using a Spectrophotometer (GenesysTM

20,

ThermoSpectronic, Rochester, NY). Blanks were initially run and also after every sixth

sample as an internal control. The following formula was used to calculate total

chlorophyll (mg g-1

): (8.02 * D663 + 20.2 * D645) * 0.1 (Arnon, 1949).

Root tissues for TNC (mg g-1

) analysis was collected first week in May for both

years. Root tissue was harvested using a bulk density sampler which extracted 154.4 cm3

core samples (10.2 cm depth) prior to sunrise to minimize any diurnal fluctuations.

Following soil removal, root tissue samples were stored at -75oC until freeze dried at -

40oC for 2-weeks to cease all metabolic activity. Samples were then ground using an A-

10 plant grinder (IKA Works, Inc., Wilmington, NC). Grounded samples were

rehydrated with 100 L of 80% ethanol (EtOH) and 2 mL of 0.1 M sodium acetate buffer

(pH 4.5) in glass test tubes 13 X 100 mm. Rehydrated samples were placed in boiling

water for 1-hour, cooled for 1-hour and repeated. Then, 2 mL of invertase (Sigma I-

4753, 433 units mg-1

) and amyloglucosidase (Sigma A-7255, 23,000 units g-1

) were

added to solution. Samples were placed in a water bath (40 – 45oC) for three days and

182

vortexed three times daily. TNC analysis was performed using Nelson (1944) and

Somogyi (1952) procedures. 25 L of aliquot was removed and two reagents (copper

and arseno-molybdate) were added to the solution. Absorbance values were measured at

520 nm using a spectrophotometer.

Soil bulk density (10.2 cm depth) was collected end of February for both years

following 24 traffic applications by extracting 154.4 cm3 soil cores. Cores were oven

dried at 105oC for 10 days to ensure complete water evaporation. The following formula

was used to calculate bulk density: dry weight of sample (g) / volume of sample (cm3).

Water infiltration analysis (Bunnell et al., 2001) was performed end of February

in both years following 24 traffic applications using a double ring infiltrometer (model

13a, Turf-Tec International, Oakland Park, Fla.). One sample was taken per plot. The

outer ring had a diameter of 30.5 cm and the inner ring, 15.2 cm. The infiltrometer was

inserted into the turfgrass canopy at a depth of 2.5 cm. Rings were then filled to the top

of the infiltrometer with 10.2 cm of water. After water vacated the center ring,

infiltration rates were recorded based on how long the water took to absorb fully into the

soil.

Data Analysis

Treatments were arranged in a randomized complete block design with six

replications. In year II, plots were re-randomized within the identical plot dimensions of

year I because no residual effects were noted during spring and summer months in year I.

All statistical computations were conducted using analysis of variance (ANOVA) within

the Statistical Analysis System (version 9.1, SAS Institute, Cary, NC). Means were

183

separated by Fisher‟s Least Significant Difference (LSD) test with an alpha of 0.05.

Year*treatment interaction occurred for winter TQ scores, however, differences were

scale changes with similar trends, therefore, pooled data from year I and II are presented.

Results

Coldest monthly surface temperatures were noted in January. For all months,

surface temperatures at 0700 were ~11.2oC colder than 0900, while surface temperatures

at 0900 were ~9.8oC colder than solar noon. However, no differences were detected for

soil temperatures between 0700 and 0900, but solar noon soil temperatures were ~3.1oC

higher than at 0700 and 0900 across all months (Table A.2). Daily maximum

temperatures for year 1 and 2 were similar with few exceptions (Figure A.1). Compared

to historical data, year I was 2.9oC below, while year II was 4.2

oC above the average

maximum temperature in December. In January and February, both years were ~4.6oC

above and ~3.5oC below historical average maximum temperature, respectively. Based

on historical minimum average temperatures, both winters were ~5.7oC warmer (Figure

A.2). Compared to year 1, year 2 had 4.7oC warmer minimum temperatures from

December to mid-January, while temperatures were similar from end of January through

February each year.

All traffic treatments TQ was below the acceptable threshold of 6 by third traffic

application, while control TQ was 7.6 (Table 10.1). By the sixth traffic application, R7

TQ was 5.3, while control, F7, F9, and R9 remained above 6. However, F9 (7.1) had a

greater TQ score than R9 (6.4), while control had the greatest TQ (7.7) score. After nine

184

Table 10.1. Turfgrass quality of ‘L93’ creeping bentgrass without (control) and with

24 foot and rolling winter traffic applications at 0700 or 0900 recorded after each 24

traffic application dates from 1 December 2005 and 2006 to 1 March 2006 and 2007.

Traffic Day 3 Day 6 Day 9 Day 12 Day 15 Day 18 Day 21 Day 24

--------------------------------Turfgrass quality (1-9)†-------------------------------

Control‡ 7.6 7.7 7.3 7.5 7.1 7.5 7.0 7.1

F7 6.6 6.9 6.3 6.0 5.4 5.1 5.0 4.8

F9 6.8 7.1 6.9 6.5 6.4 6.5 6.3 5.9

R7 5.7 5.3 5.3 5.2 4.3 4.1 3.8 3.7

R9 6.8 6.4 6.3 6.4 6.2 5.6 5.8 5.4

LSD 0.44§

0.53 0.54 0.51 0.46 0.50 0.51 0.48 †Turfgrass quality based on a scale of 1 - 9, 1 = brown/dead turfgrass, 6 = minimally

acceptable turfgrass, 9 = ideal green, healthy turfgrass. ‡Abbreviations: Control = No traffic, F7 = Foot traffic at 0700, F9 = Foot traffic at 0900,

R7 = Rolling traffic at 0700, R9 = Rolling traffic at 0900, LSD = least significant

difference. Foot traffic consisted of ~75 steps using SP-4 Saddle Nike golf shoes (soft-

spiked sole). Rolling traffic was accomplished using a Toro® Greensmaster® 800 walk

behind mower. §Values within a column followed by the same letter are not significantly different at



traffic applications, the R7 treatment had a 5.3 TQ score, while F7 had a TQ score of 6.3.

Also, R9 TQ was 6.3, while F9 TQ was 6.9. Similar trends continued from day 12

through day 24 ratings as R7 reduced TQ by ~1.0 units compared to F7 TQ. Visual TQ

for R9 on two rating dates (day 18 and 24) showed a 0.9 and 0.5 unit decline compared to

F9 TQ. On the last traffic application date, R7 had TQ of 3.7, while F7‟s TQ was 4.8.

On all rating dates, R7 showed a ~1.4 unit TQ decrease than R9, while F7 reduced TQ by

~1.1 units compared to F9 on most rating dates. Except R7 (5.8), all other treatments

185

Table 10.2. Turfgrass quality of ‘L93’ creeping bentgrass without (control)

and with 24 foot and rolling winter traffic applications at 0700 or 0900

recorded weekly and averaged per month from March to August, 2006 and

2007.

Traffic March April May June July August

----------------------------Turfgrass Quality (1-9)†-----------------------

Control‡ 7.1 7.8 7.9 7.6 7.5 6.6

F7 6.2 7.3 7.8 7.6 7.5 6.4

F9 6.5 7.3 7.7 7.3 7.6 6.3

R7 5.8 7.0 7.7 7.3 7.6 6.4

R9 6.5 7.3 7.7 7.4 7.4 6.6

LSD 0.30§ 0.33 NS NS NS NS

†Turfgrass quality based on a scale of 1 - 9, 1 = brown/dead turfgrass, 6 =

minimally acceptable turfgrass, 9 = ideal green, healthy turfgrass. ‡Abbreviations: Control = No traffic, F7 = Foot traffic at 0700, F9 = Foot traffic at

0900, R7 = Rolling traffic at 0700, R9 = Rolling traffic at 0900, LSD = least

significant difference, NS = not significant. Foot traffic consisted of ~75 steps

using SP-4 Saddle Nike golf shoes (soft-spiked sole). Rolling traffic was

accomplished using a Toro® Greensmaster® 800 walk behind mower. §Values within a column followed by the same letter are not significantly different



reached acceptable TQ by March (Table 10.2). By April, all treatments were above the

acceptable TQ threshold of 6 indicating bentgrass had visually recovered from any winter

traffic damage. No TQ differences were noted from May to August ratings, however, TQ

scores began to decline for all treatments in August due to the onset of summer stress not

influenced by this winter study.

Winter traffic significantly impacted clipping yield (Table 10.3). In December,

compared to the control, F7 and F9 reduced clipping yield ~6.5%, while R7 and R9

reduced clipping yield ~24%, respectively. Similar trends continued in January and

186


) of ‘L93’ creeping bentgrass without

(control) and with 24 foot and rolling winter traffic applications at 0700 or

0900 in winter, spring, and summer months in year I and II.

Traffic December January February May August

------------------------------Clipping yield (g m-2

)-------------------------

Control† 1.74 1.55 1.27 1.31 1.27

F7 1.71 1.27 1.21 1.27 1.28

F9 1.57 1.38 1.16 1.23 1.24

R7 1.50 1.10 1.04 1.32 1.42

R9 1.32 1.04 0.95 1.26 1.32

LSD 0.17‡ 0.23 0.22 NS NS

†Abbreviations: Control = No traffic, F7 = Foot traffic at 0700, F9 = Foot traffic at




accomplished using a Toro® Greensmaster® 800 walk behind mower. ‡Values within a column followed by the same letter are not significantly different



February indicating rolling traffic negatively impacted shoot growth greater than foot

traffic. In February, no differences were noted between foot traffic and the control, while

R7 and R9 reduced clipping yield ~28% compared to the control. No residual effects

from winter traffic on shoot growth were noted in May or August.

Shoot chlorophyll concentration was not impacted in December or January, but

the control had ~18% higher chlorophyll concentration compared to F7 in February

(Table 10.4). In May and August, no differences were noted for chlorophyll

concentration indicating no winter traffic residual effects. After 24 traffic applications

(foot or rolling) at 0700 or 0900, no impact was noted on bulk density or water

infiltration rates (Table 10.5). Also, root TNC in May was unaffected by any winter

traffic treatments (Table 10.5).

187

Table 10.4. Chlorophyll (mg g-1

) concentration of ‘L93’ creeping bentgrass

without (control) and with 24 foot and rolling winter traffic applications at

0700 or 0900 recorded in winter, spring, and summer months in year I and

II.

Traffic December January February May August

-------------------------------Chlorophyll (mg g-1

)------------------------

Control† 1.91 1.60 1.34 2.68 2.66

F7 2.07 1.54 1.14 2.77 2.66

F9 1.97 1.58 1.21 2.59 2.70

R7 2.01 1.53 1.23 2.58 2.78

R9 2.04 1.53 1.21 2.72 2.67

LSD NS NS 0.13‡ NS NS

†Abbreviations: Control = No traffic, F7 = Foot traffic at 0700, F9 = Foot traffic

at 0900, R7 = Rolling traffic at 0700, R9 = Rolling traffic at 0900, LSD = least



accomplished using a Toro® Greensmaster® 800 walk behind mower. ‡Values within a column followed by the same letter are not significantly



Table 10.5. Soil bulk density (g cm-3

) and infiltration rates (cm h-1

) collected

end of February and root total non-structural carbohydrates (TNC) (mg g-1

)

collected in May following 24 treatment application dates with and without

(control) foot and rolling traffic at 0700 or 0900 from 1 December 2005 and

2006 to 1 March 2006 and 2007.

Traffic Bulk Density Infiltration Root TNC

Control† 1.72 4.20 47.37

F7 1.71 4.80 43.72

F9 1.72 5.34 48.69

R7 1.71 4.30 46.62

R9 1.70 4.58 40.03

LSD NS NS NS †Abbreviations: Control = No traffic, F7 = Foot traffic at 0700, F9 = Foot traffic at




accomplished using a Toro Greensmaster 800 walk behind mower.


188

Discussion

When temperatures are at or near freezing, decisions about when to allow normal

golf course management operations, such as course set-up, are generally experience-

based. Previous research was lacking on winter traffic damage to bentgrass greens and

subsequent performance in the spring and summer in the southern transition zone where

golf play continues through winter months. Based on these results, time and type of

traffic negatively impacted bentgrass winter performance and playability. By day 24, R7

and R9 decreased TQ by 1.1 and 0.5 units compared to F7 and F9, respectively. Also, F7

and R7 decreased TQ by 1.1 and 1.7 units compared to F9 and R9, respectively. This can

be attributed to more complete frost dissipation as frost melt had occurred by 0900 on

cloudless mornings. Surface temperatures on simulated traffic days were consistently

below 0oC at 0700, while surface temperatures at 0900 were >6.8

oC. Regardless of

traffic type, all treatments were deemed unacceptable following 24 traffic treatments on

the coldest days from December to February. However, F9 TQ was at or near the

acceptable threshold throughout the winter months. Averaged across all TQ rating dates,

R7 decreased TQ by ~1.1 units compared to F7. Rolling traffic had more surface

discoloration than foot traffic due to heavier impacts of the mower. The contact area of

the roller was ~115 cm2 (46 cm roller width with 2.5 cm of the roller consistently

contacting the turfgrass surface) with a pressure of 0.80 kg cm-2

, while one foot traffic

pressure was 0.31 kg cm-2

with a contact area of 240 cm2. Therefore, the walk behind

mower applied nearly three times the pressure of foot traffic. Carrow and Petrovic

(1992) also noted added weight increased wear injury.

189

Rolling traffic reduced bentgrass shoot growth ~28% compared to control,

however, no differences in chlorophyll, bulk density, or water infiltration were detected

between treatments in February. Since bulk density was unaffected following 24 winter

traffic applications, the primary stress in this study was wear and not soil compaction as

reported by Carrow and Petrovic, 1992. Traffic stress on Kentucky bluegrass (Poa

Pratensis L.) also reduced shoot growth (Ervin and Koski, 2001). Shoot growth

suppression can be attributed to weight being applied to the bentgrass surface with

possible physical damages to shoot tissues. Further studies are needed to specifically

examine winter traffic damages to above ground tissues. Spring and summer TQ, root

TNC, and shoot chlorophyll data indicate winter traffic damage is limited to winter and

early spring months. By mid- to late-spring and throughout summer, all plots fully

recovered.

Results obtained in this study may vary on other field sites due to variable micro-

environments on golf courses, in particular, shade. While not examined in this study,

shaded areas may be more difficult for winter management because surface frost

dissipation is slower than greens receiving full early morning sunlight. Also, slopes

facing north or northeast receive less direct sunlight during winter morning hours and are

more prone to winter injury due to prolonged frost periods (McCarty et al., 2005).

Winter shade, in combination with winter traffic, is potentially damaging due to shorter

daylengths, reduced light intensities, and solar elevation angles. These factors can

enhance frost accumulation and prolong frost coverage.

190

Conclusion

Turfgrass managers should carefully consider whether to allow traffic on turfgrass

surfaces when frost is present. Traffic weight appears to be the contributing factor for

increased surface discoloration was weight of traffic. Although, foot traffic was less

damaging than equipment traffic, some surface discoloration was noted. Even at 0900

when temperatures were above freezing and frost had dissipated, bentgrass injury was

observed. However, by late spring and summer, TQ differences were no longer detected.

Therefore, if winter injury occurs on a bentgrass green in the eastern part of the transition

zone, full recovery should be expected.

Future studies could investigate winter traffic impacts at later time periods (i.e.,

0730, 0800, 0830, 0900, or 0930) and temperature ranges (i.e., -1-2

oC, 2-4

oC, or 5-7

oC) to

monitor the traffic impacts. This type of study would provide turfgrass managers with

information that would help them manage play and maintenance while minimizing injury

to bentgrass putting greens during winter months. In addition, creeping bentgrass

cultivars may perform differently in response to winter traffic due to different root zone

mixtures, fertility regimes (i.e., nitrogen, calcium, and potassium), and equipment type.

These types of studies could also be conducted on warm-season turfgrass putting greens

either overseeded or painted in areas where multiple light to medium frosts occur during

winter months. Finally, the impacts of lightly syringing greens to dissipate frost

accumulation and reduce traffic damage warrants investigations.

191

CHAPTER XI

SUMMARY AND PERSPECTIVES

Primary objectives of this dissertation were to determine the genetic diversity of

bermudagrasses grown in full-sunlight and shade, impacts of shade and winter cultural

practices on bermudagrass spring transition, management recommendations to enhance

bermudagrass putting greens under shade, and the impact different types of light on

warm-season turfgrasses. Secondary objectives of this dissertation were to determine

winter shade and traffic impacts on creeping bentgrass putting greens.

A field study determined the morphological and physiological characteristics of

42 bermudagrass cultivars selected from the 2002 National Turfgrass Evaluation Program

(NTEP) in spring, summer, and fall. Experimental bermudagrass cultivars from breeding

programs were comparable, and at times, out-performed industry standards based on

parameters measured in the spring, summer, and fall. In a greenhouse study, the same 42

bermudagrass cultivars were subjected to 64% continuous artificial shade for 60 days.

Cultivars with best shade-tolerance were Celebration, TiftNo.4, TiftNo.1, and

Transcontinental, while most shade-sensitive cultivars included SWI-1014, Arizona

Common, Sundevil, SR 9554, GN-1, and Patriot. Both of these studies demonstrate

genetic variability exists within bermudagrass and future improvement of breeding

improved bermudagrass cultivars should be expected.

In two lysimeter projects, fairway and ultradwarf bermudagrasses were subjected

to shade in late-winter and continued shade stress through spring and summer months.

192

Also, for the ultradwarf bermudagrass, various winter cultural practices were investigated

to determine best winter management practices. For fairway type grasses, Celebration

and TiftNo.4 did not show significant SGU delays due to shade in year II, however,

Yukon and Riviera delayed SGU 11% and 50% compared to full-sunlight treatments on 9

May 2007. Celebration and TiftNo.4 showed a ~1.3 and ~1.7 unit TQ increase compared

to other cultivars in July when grown in shade, however, all cultivars TQ was below the

acceptable threshold of 7 by 31 July. In another lysimeter study, regardless of winter

cultural practice, shade reduced TifEagle bermudagrass SGU and summer TQ ratings

compared to full-sunlight treatment. However, colorant use enhanced SGU ratings

compared to overseed and dormant treatments under full-sunlight and shade. This study

indicates colorant-use may provide an alternative to overseeding for bermudagrass by

providing adequate winter color at certain sites and a stronger bermudagrass base

compared to overseeding.

A two-year field study determined best management practices to enhance a

Champion bermudagrass putting green under shade. Treatments included 55% full-day

shade, TE applications (0.05 kg a.i. ha-1

2wk-1

), iron (Fe) applications (2.7 kg a.i. ha-1

2wk-1

), and N applications as urea (46-0-0) at rates of 147, 293, and 437 kg ha-1

yr-1

.

Results indicate reducing N rates linearly increased TQ scores under 55% full-day shade.

Also, applying TE resulted in a linear TQ increase for full-sunlight and shade-grown

Champion bermudagrass. Iron applications had minimal impacts on parameters

measured. In conclusion, while adjusting chemical and cultural management practices

193

reduced shade stress symptoms, 55% full-day shade for three months resulted in

unacceptable quality, regardless of management practices.

In the greenhouse, two repeated studies were conducted to understand the

physiological and morphological responses of Diamond zoysiagrass, Sea Isle 2000

seashore paspalum, Tifway bermudagrass, and Celebration bermudagrass to various light

spectral qualities. Light treatments included a full-sunlight control and four different

color shade cloths filtering wavelengths 560 - 720 nm (blue shade cloth), 360 – 520 nm

(yellow shade cloth), 360 - 560 nm (red shade cloth) and 360-720nm (black shade cloth).

Percent light reduction for each cloth was ~65%. Overall, black shade most negatively




This study implies different types of shade significantly impact the performance of warm-

season turfgrasses.

A winter field study was conducted to evaluate winter shade tolerance of „L93‟

creeping bentgrass under various reduced light environments (55% and 95%), including

effects of morning vs. afternoon shade, effect of trinexapac-ethyl (TE) (4-(cyclopropyl- -

hydroxy-methylene)-3,5-dioxy-cyclohexanecarboxylic acid ethyl ester) application on

shade tolerance, and summer month performance following a winter shade environment.

Under shade stress, applying TE every two weeks during winter negatively impacted

bentgrass growth and color, while morning or afternoon shade minimally impacted

parameters measured. Based on this study, moderate to heavy winter shade may not limit

194

creeping bentgrass performance as a putting green in the transition zone. In a winter

traffic field study, treatments consisted of no traffic (control), foot traffic, and walk

behind mower traffic (rolling) at 0700 and 0900 when canopy temperatures were at or

below 0oC. The 0700 rolling traffic treatment decreased TQ by ~1.1 units compared to

foot traffic at 0700. However, by the end of March, all treatments had acceptable TQ.

This study indicates bentgrass damage due to winter traffic is limited to winter and early

spring months and full recovery should be expected by summer.

Shade is a unique stress. In a natural environment, shade is dynamic and ever-

changing making it very difficult to capture this unique environment through traditional

field and greenhouse studies. Due to this, conducting shade research is difficult and

perhaps an explanation why bermudagrass shade stress research is minimal. Although

this dissertation has addressed many gaps in the literature, many questions remain

regarding bermudagrass and shade.

This dissertation has shown that fairway type bermudagrasses vary in response to

shade stress. Future studies to establish why these bermudagrass cultivars are relatively

shade-tolerant include determining photosynthetic rates, characterizing GA levels (i.e.,

GA1, GA12, or GA53 via mass spectroscopy), exploring anatomical development, and

investigating the importance of sunflecks and its contribution to photosynthesis. While

fairway type bermudagrasses are diverse in response to shade, ultradwarf bermudagrass

shade research is minimal. Although ultradwarf bermudagrasses are gaining popularity,

relative shade-tolerance of many of these cultivars remains unknown.

195

The majority of shade research focusing on light quality has been greenhouse

studies, therefore, field evaluations are warranted to confirm results obtained from an

artificial greenhouse environment. Also, comparing the response of turfgrass species

and/or cultivars to altered R:FR ratios is lacking. This dissertation has indicated different

light spectrums impact warm-season turfgrasses differently. However, the same type of

light was filtered all day, which is a limitation of this study. A future field study of

interest would be to compare how alternating between different types of spectral shade in

the morning or afternoon effect turfgrass performance.

While this dissertation and previous research have proven N reductions is

beneficial for turfgrass shade performance, many question still remain regarding fertility

regimes when shade is problematic. For example, while reducing N is prudent, numerous

N forms and sources exist in the market. Future studies addressing how N form (liquid,

granular, combination of both forms) and N type (calcium nitrate, ammonium sulfate,

urea, and ammonium nitrate) effect turfgrass growth and development under shade is

warranted. Also, investigating other macro and micronutrient rates for shade-tolerance

improvement is needed. Another nutrient of interest is silicon (Si). In other plant

disciplines, Si has improved salt stress in rice (Matoh et al., 1986), barley (Liang et al.,

1996), cucumber (Zhu et al., 2004), tomato (Romero-Aranda et al., 2006), and wheat

(Ahmad et al., 1992) and aluminum stress in Zea Mays (Barcelo et al., 1993; Corrales et

al., 1997). Silicon has also been proven to enhance drought tolerance and photosynthetic

capacity in bentgrass (Schmidt et al., 1999). Future studies determining the importance

of Si as a stress reducing nutrient in turfgrass is needed.

196

Plant growth regulator applications have become a routine component of turfgrass

management. This dissertation and previous research has firmly established TE improves

warm- and cool-season turfgrasses response to shade when temperatures are optimal for

growth. However, questions still remain about PGR applications under shade stress.

Future studies investigating various TE rates, intervals of TE applications, tank mixing

TE with other PGRs, and comparing TE to other GA inhibiting PGRs to further improve

the response of turfgrasses under shade stress are needed. Perhaps the most significant

aspect ignored in this dissertation and previous bermudagrass shade research is traffic

effects when TE is used. Adding a traffic stress component when applying TE under

shade stress would be a practical research area to pursue with great benefit to the

industry.

Another interesting area to pursue in shade research is to study the impact of tree

roots and air restriction on the performance of turfgrasses. Only two studies found have

focused on tree root competition with turfgrasses (Whitcomb, 1972; Whitcomb and

Roberts, 1973). However, difficulty in quantifying exactly how much water and nutrients

a tree root system out-competes a turfgrass root system is a limiting factor for this type of

future research. Previous research has established that air restriction is a stress

independent of shade, however, the few studies that exist have been limited to only a few

turfgrass cultivars. Future studies of interest would be to determine turfgrass species

and/or cultivar genetic variation to wind restriction stress.

Finally, utilizing bio-technology may be a future avenue in improving responses

of turfgrasses to shade stress. At Ohio State University, Yan (2007) overexpressed GA 2-

197

oxidase genes responsible for gibberellic acid production, overexpressed PHYB genes

from Arabidopsis causing dwarfing characteristics, and overexpressed BAS1 gene

regulating brassinosteroid levels causing dwarf-type growth. For all genes

overexpressed, results indicated improved shade tolerance in creeping bentgrass.

Continuing to explore the potential of transgenic approaches and determine the feasibility

of this technology to enhance shade tolerance of existing turfgrass species would be

beneficial.

198

APPENDICES

199

Appendix A

Additional Tables and Figures

Table A.1. Bermudagrass (Cynodon dactylon (L.) Pers.) cultivars selected for a field and greenhouse

study to evaluate morphological and physiological characteristics and shade-tolerance at the

Clemson University field research plots and greenhouse research complex.

Cultivar Type Sponsor Address

„Sunstar‟ Seeded Lesco, Inc. 1301 East 9th St., Suite 1300, Cleveland, OH 44114

„B-14‟ Seeded Lesco, Inc. 1301 East 9th St., Suite 1300, Cleveland, OH 44114

„SWI-1003' Seeded Seeds West, Inc. 508 East 16th Street, Yuma, AZ 85365

„SWI-1012‟ Seeded Seeds West, Inc. 508 East 16th Street, Yuma, AZ 85365

„'SWI-1014‟ Seeded Seeds West, Inc. 508 East 16th Street, Yuma, AZ 85365





„Arizona

Common‟ Seeded Standard Entry ------------------------------------------

„NuMex Sahara‟ Seeded Standard Entry ------------------------------------------

„Princess 77‟ Seeded Standard Entry ------------------------------------------

„Mohawk‟ Seeded Seeds West, Inc. 508 East 16th Street, Yuma, AZ 85365

„FMC-6‟ Seeded Seeds West, Inc. 508 East 16th Street, Yuma, AZ 85365

„SWI-1001 Seeded Seeds West, Inc. 508 East 16th Street, Yuma, AZ 85365

„Tift No.3‟ Vegetat-

ive

Wayne Hanna -- USDA-

ARS P.O. Box 748, Tifton, GA 31793

„Tift No.4‟ Vegetat-

ive



„Tifway‟ Vegetat-

ive Standard Entry ------------------------------------------

„Midlawn‟ Vegetat-

ive Mississippi State University P.O. Box 9555, Mississippi State, MS 39762

„Tifsport‟ Vegetat-

ive Standard Entry ------------------------------------------

„Sundevil‟ Seeded Jacklin Seed/Simplot 5300 W. Riverbend Ave., Post Falls, ID 83854

„Southern Star‟ Seeded Jacklin Seed/Simplot 5300 W. Riverbend Ave., Post Falls, ID 83854

„MS-Choice‟ Vegetat-

ive Mississippi State University P.O. Box 9555, Mississippi State, MS 39762

„Transcontinental‟ Seeded Turf-Seed, Inc. 7644 Keene Rd. NE, Gervais, OR 97026

„CIS-CD5‟ Seeded DLF International Seeds 175 W. H St., P.O. Box 229, Halsey, OR 97348



„Panama‟ Seeded Barenbrug USA 33477 HWY 99E, P.O. Box 239, Tangent, OR 97389

„La Paloma‟ Seeded Seed Research of OR, Inc. 27630 Llewellyn Rd., Corvallis, OR 97330

200

Table A.1. Bermudagrass (Cynodon dactylon (L.) Pers.) cultivars selected for a field and greenhouse

study to evaluate morphological and physiological characteristics and shade-tolerance at the

Clemson University field research plots and greenhouse research complex (continued).

„SR 9554‟ Seeded Seed Research of OR, Inc. 27630 Llewellyn Rd., Corvallis, OR 97330

„Yukon‟ Seeded Seed Research of OR, Inc. 27630 Llewellyn Rd., Corvallis, OR 97330

„Aussie Green‟ Vegetat-

ive Greg Norman Turf Co. 4366 E. Kinsey Rd, Avon Park, FL 33825

„GN-1‟ Vegetat-

ive Greg Norman Turf Co. 4366 E. Kinsey Rd, Avon Park, FL 33825

„Premier‟ Vegetat-

ive Trinity Turf Nursery 17199 Zipper Rd., Pilot Point, TX 76258

„Ashmore‟ Vegetat-

ive Blue Moon Farms, LLC 811 Mountain River Rd., Lebanon, OR 87355

„Patriot‟ Vegetat-

ive Oklahoma State University 136 Ag Hall, Stillwater, OK 74078

„OKC 70-18‟ Vegetat-

ive Oklahoma State University 136 Ag Hall, Stillwater, OK 74078

„Celebration‟ Vegetat-

ive Sod Solutions P.O. Box 460, Mt. Pleasant, SC 29465

„TiftNo.1‟ Seeded



„TiftNo.2‟ Seeded



„Sunbird‟ Seeded Turf-Seed, Inc. 7644 Keene Rd. NE, Gervais, OR 97026

201

Table A.2. Average monthly surface and soil (7.6 cm depth) temperatures (oC)

of ‘L93’ creeping bentgrass during each 24 traffic treatment applications at

0700, 0900, and solar noon from 1 December, 2005 and 2006 to 1 March 2006

and 2007.

Surface temperatures (oC) Soil temperatures (

oC)

Time December January February December January February

0700 -4.0 -3.1 -3.5 3.3 3.5 2.6

0900 8.3 6.8 7.8 3.1 3.8 2.6

Solar

Noon 20.0 17.0 15.2 6.0 6.7 6.1

LSD 2.5† 2.5 2.6 1.3 1.7 1.5



LSD = least significant difference.

Figure A.1. Daily and historical average maximum temperatures at Clemson University,

Clemson, SC in year I and II from 1 December to 28 February 2005 – 2007.

0

5

10

15

20

25

30

Year 1

Year 2

Average

1 December to 28 February 2005 - 2007

oC

202

Figure A.2. Daily and historical average minimum temperatures at Clemson University,

Clemson, SC in year I and II from 1 December to 28 February 2005 – 2007.

-10

-5

0

5

10

15

Year 1

Year 2

Average

1 December to 28 February 2005 - 2007

oC

oC

203

Appendix B

Chlorophyll Extraction with DMSO

1. Weigh 0.1 g fresh shoot tissue into Erlenmyer flasks.

2. Add 10 mL of Dimethyl Sulfoxide to each flask. Cover with rubber stopper.

3. Incubate in 65 C water shake bath for 1.5 h.

4. Transfer extract into spectrophotometer using pipetter.

5. Measure and record absorbance values at 663 nm and 645 nm wavelengths.

6. Chlorophyll content is determined by the following formula (Arnon, 1949).

(20.2 * D645 + 8.02 * D663) * 0.1 = mg chlorophyll g-1

fresh tissue

D663 and 645 = absorbance values at given wavelengths

204

Appendix C

Procedure for Nelson‟s Assay for TNC Analysis

Aliquot preparation

1. Weigh 50 mg dry tissue sample in 13 x 100 mm test tube.

2. Add 100 µl of 80% ethanol.

3. Add 2 ml of 0.1 M sodium acetate buffer.

4. Place test tubes in boiling water for 1 h; allow cooling for 1 h, and repeat. Allow

solution to cool before adding enzymes.

5. Add 1.0 ml of each enzyme solution. Keep enzyme solutions on ice.

a. Invertase (Sigma I-4753, 433 units mg-1

)

- 5 units / ml in 0.1 M acetate buffer

b. Amyloglucosidase (Sigma A-7255, 23,000 units g-1

)

- 50 units / ml in 0.1 M acetate buffer

6. Incubate for 3 days at 40-45 C and vortex 3 times day-1

.

7. Allow to settle until clear.

8. Remove 25 µl of aliquot for TNC analysis.

205

Buffers, Reagents, and Standard Glucose Curves

Sodium Acetate Buffer

1. For 2000 ml of 0.1 M buffer, weigh 5.56 g of sodium acetate.

2. Dissolve in approximately 1600 ml deionized water.

3. Adjust pH to 4.5 using 1 N acetic acid.

4. Bring to 2000 ml volume.

5. Store at 3 C.

Copper Reagent

1. Dissolve 28 g of anhydrous sodium phosphate dibasic (Na2HPO4) and 4 g K-Na-

tartate (Rochelle salt) in approximately 650 ml of deionized water.

2. Add 100 ml of 1 N NaOH (4g NaOH 100 ml-1

H2O) while stirring.

3. Add 80 ml of 10% copper sulfate (8g CuSO4 80 ml-1

H2O)

4. Add 180 g of anhydrous Na2SO4.

5. Bring to 1000 ml volume and mix well.

6. Allow to settle at room temperature for 24 h.

7. Decant and save clear supernatant.

8. Store in brown bottle at room temperature.

Arseno-Molybdate (ASMO) Reagent

1. Dissolve 25 g of ammonium molybdate (NH4MoO4) in approximately 400 ml.

206

2. Add 21 ml of concentrated sulfuric acid.

3. Add 3 g of sodium arsenate (Na2HAsO4•7H2O) dissolved in 25 ml of deionized water.

4. Bring to 500 ml and mix well.

5. Incubate at 37 C for 24-48 h.

6. Store in brown bottle at room temperature.

Glucose Standards

Glucose Concentration glucose (g l-1

) Dilution for 10 ml of Standard

0.8 µmol 100 μl-1

(stock) 1.4408 g l-1

10.00 ml stock : 0.00 ml water

0.7 µmol 100 μl-1

(stock) 1.2607 g l-1


0.6 µmol 100 μl-1

(stock) 1.0806 g l-1


0.5 µmol 100 μl-1

(stock) 0.9005 g l-1


0.4 µmol 100 μl-1

(stock) 0.7204 g l-1


0.3 µmol 100 μl-1

(stock) 0.5403 g l-1


0.2 µmol 100 μl-1

(stock) 0.3602 g l-1


0.1 µmol 100 μl-1

(stock) 0.1801 g l-1


0.0 µmol 100 μl-1

(stock) 0.0000 g l-1


TNC Calculation

1. Pipette 25 µl of aliquot (samples and glucose standards) into 13 x 100 mm test tubes.

2. Add 1.0 ml of copper reagent, mix, and place in boiling water bath for 20 minutes.

3. Remove samples and allow cooling for 5 minutes in room temperature water bath.

207

4. Add 0.5 ml of ASMO, mix well with vortex, and pipette into cuvettes.

5. Read absorbance at 520 nm.

6. Calculate linear regression of glucose standard curve.

7. Solve for glucose concentration using linear regression equation and absorbance

value.

Figure C.1. Standard curve used in Nelson‟s assay for determining total nonstructural

carbohydrate content in bermudagrass and bentgrass shoots and roots.

y = 0.8805x - 0.0288

R2 = 0.9704

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 0.2 0.4 0.6 0.8 1

Glucose standard (μg glucose 100 μL-1

)

Ab

sorb

an

ce (

52

0 n

m)

208

Appendix D

Illustrations

Illustration D.1. TiftNo.5 bermudagrass anatomical features including bundle sheath (a),

mesophyll cells (b), vascular bundle (c), and epidermal cells (d). Image recorded on 20

December 2005 at the Clemson University Research Park, Clemson, SC, using a SEM-

Hitachi S3500N electron microscope.

D

B

A

C

209

Illustration D.2. Overview of 42 bermudagrass cultivars from the 2002 National

Turfgrass Evaluation Program located at the Clemson University field research plots.

210

Illustration D.3. Spring green-up comparison of „Riviera‟ (left) and „Tifway‟ (right)

bermudagrass selected from the 2002 National Turfgrass Evaluation Program at the

Clemson University field research plots. Image recorded: 18 April 2006.

Illustration D.4. Spring green-up comparison of „Midlawn‟ (left) and „Celebration‟ (right)

bermudagrass selected from the 2002 National Turfgrass Evaluation Program at the

Clemson University field research plots. Image recorded: 14 April 2007.

211

Illustration D.5. Percent dormancy comparison of „Aussie Green‟ (top-left), „Celebration‟

(top-right), and „TifSport‟ (bottom) bermudagrass selected from the 2002 National

Turfgrass Evaluation Program at the Clemson University field research plots. Image

recorded: 21 November 2006.

212

Illustration D.6. Overview of a greenhouse study investigating the impact of shade on 42

bermudagrass cultivars at the Clemson University greenhouse complex.

213

Illustration D.7. „Tifway‟ (a), „TiftNo.4‟ (b), and „Celebration‟ (c) bermudagrass

response to 5 weeks of 64% continuous shade at the Clemson University greenhouse

research complex.

A

C

B

214

Illustration D.8. Root biomass of Celebration (left) and Tifway (right) bermudagrass

following 8 weeks of 55% continuous shade at the Clemson University greenhouse

complex.

215

Illustration D.9. Overview of a shade structure to investigate the response of

bermudagrass spring transition impacted by 55% continuous shade located at the

Clemson University field research plots.

216

Illustration D.10. Comparison of „Celebration‟ grown under full-sunlight (a) and 55%

continuous shade (b), TiftNo.4 grown under full-sunlight (c) and 55% continuous shade

(d) and „Tifway‟ grown under full-sunlight (e) and 55% continuous shade (f) adjacent to

the Clemson University field research plots.

D

B

C

A

E F

217

Illustration D.11. Spring performance comparison of „TifEagle‟ bermudagrass treated

with a colorant (left) and untreated (right) in the winter grown under full-sunlight. Image

recorded on May 1, 2007.

Illustration D.12. Spring performance comparison of „TifEagle‟ bermudagrass

overseeded in the winter grown in full-sunlight (left) and 55% continuous shade (right).

Image recorded on May 1, 2007.

218

Illustration D.13. Overview of „Champion‟ bermudagrass shade study at the Clemson

University field research plots.

219

Illustration D.14. „Champion‟ bermudagrass response to 147 (a), 294 (b), and 441 (c) kg

a.i. ha-1

yr-1

of nitrogen (urea) when grown under 55% continuous shade for 8 weeks at

the Clemson University field research plots.

A B

C

220

Illustration D.15. „Champion‟ bermudagrass response to 147 kg a.i. ha-1

yr-1

of nitrogen

(urea) with TE (0.02 kg ha-1

2wk-1

) (a) and 294 kg a.i. ha-1

yr-1

of nitrogen (urea) without

TE (b) when grown under 55% continuous shade for 8 weeks at the Clemson University

field research plots.

A B

221

Illustration D.16. Overview of a greenhouse study investigating the impacts of different

light spectral qualities on various warm-season turfgrasses at the Clemson University

greenhouse complex.

222

Illustration D.17. Root biomass comparison of „Sea Isle 2000‟ seashore paspalum (top-

left), „Celebration‟ bermudagrass (top-right), „Tifway‟ bermudagrass (bottom-left) and

„Diamond‟ zoysiagrass (bottom-right) grown under full-sunlight for eight weeks in the

Clemson University greenhouse complex. Image recorded: 13 June 2007.

223

Illustration D.18. Visual quality comparison of „Diamond‟ zoysiagrass (top-left), „Sea

Isle 2000‟ seashore paspalum (top-right), „Celebration‟ bermudagrass (bottom-left),

„Tifway‟ bermudagrass (bottom-right) grown under blue shade for six weeks in the

Clemson University greenhouse complex. Image recorded: 20 August 2007.

224

Illustration D.19. Overview of „L93‟ creeping bentgrass putting green shade study

initiated at the Clemson University field research plots.

225

Illustration D.20. „L93‟ creeping bentgrass response to rolling traffic at 0700 (a) and

rolling traffic at 0900 (b) at the Clemson University field research plots.

A B

226

Illustration D.21. „L93‟ creeping bentgrass response to rolling traffic at 0700 (a) and foot

traffic at 0700 (b) at the Clemson University field research plots.

A B

227

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