the effect of genotype, environment and time of harvest on

The effect of genotype, environment and time of harvest on

sugarcane yields in Florida, USA

R.A. Gilbert a,*, J.M. Shine Jr.b, J.D. Miller c, R.W. Rice b, C.R. Rainbolt a

aUniversity of Florida, EREC, 3200 E. Palm Beach Road, Belle Glade, FL 33430, USAb Sugar Cane Growers Cooperative of Florida, P.O. Box 666, Belle Glade, FL 33430, USAcUSDA-ARS, Sugarcane Field Station, 12990 US Hwy. 441, Canal Point, FL 33438, USA

Received 11 February 2005; received in revised form 11 February 2005; accepted 12 February 2005

Abstract

Sugarcane (Saccharum spp.) is grown across different production environments and is harvested over a 5-month (mid-

October–mid-March) period in Florida. While many studies have examined genotype � environment interactions and their

implications for breeding program design, knowledge is limited regarding interactions of genotype, environment and time of

harvest and their implications for growers. Three non-confounded data sets (‘‘case studies’’) were analyzed to determine the

effects of these three factors on kilograms of sugar per ton (KST), tons of cane per hectare (TCH) and tons of sugar per hectare

(TSH) for recently released cultivars in south Florida. Cultivar (genotype), environment, time of harvest and their interactions

had significant effects on KST, TCH and TSH. Sugarcane KST and TSH were reduced by 28 and 29%, respectively, when

harvested in mid-October compared to optimum harvest dates in February. TSH varied from 2 to 46% across environments. The

Lakeview ‘‘warmland’’ site near Lake Okeechobee recorded significantly higher TCH and TSH than other sites, and cultivars

CP88-1508 and CP88-1834 recorded higher relative yields at Lakeview. Cultivar TSH varied up to 51% across the case studies.

CP89-2143 had significantly higher KST than other cultivars in all 21 pairwise comparisons in the three case studies, and a

remarkably high, stable KST ranking across environments. Growers in the Everglades Agricultural Area interested in improving

sugarcane crop sucrose concentration should plant CP89-2143. However, significant genotype � environment interactions for

other cultivars support continued multi-locational evaluation of sugarcane germplasm both during the breeding program and

following cultivar release.

# 2005 Elsevier B.V. All rights reserved.

Keywords: Sugarcane; Genotype; Environment; Time of harvest

www.elsevier.com/locate/fcr

Field Crops Research 95 (2006) 156–170

* Corresponding author. Tel.: +1 561 993 1535;

fax: +1 561 993 1582.

E-mail address: [email protected] (R.A. Gilbert).

0378-4290/$ – see front matter # 2005 Elsevier B.V. All rights reserved

doi:10.1016/j.fcr.2005.02.006

1. Introduction

Sugarcane (Saccharum spp.) is harvested over a

5-month period (mid-October–mid-March), across

differing agroecologies in the Everglades Agricultural

Area (EAA) of south Florida. Both environment

.

R.A. Gilbert et al. / Field Crops Research 95 (2006) 156–170 157

and time of harvest influence sugarcane sucrose

accumulation. Growers must factor in sugarcane

genotype and environment when scheduling their

harvests.

Environmental effects on sugarcane yields may be

due to differing nutrient deficiencies (Anderson et al.,

1995), disease pressures (Magarey and Mewing, 1994)

or climatic differences between locations. However,

the vast majority of studies addressing the effects of

location on sugarcane yields have focused on the

interaction of genotype � environment. Although

numerous studies have reported significant G � E

interactions and recommended sugarcane selection in

differing environments (Arceneaux and Hebert, 1943;

Glaz et al., 1985; Milligan et al., 1990; Bull et al.,

1992; Mirzawan et al., 1994; Bissessur et al., 2000),

other studies have concluded that the number of

environments in sugarcane breeding programs could

be reduced (Gravois and Milligan, 1992; Milligan,

1994; Jackson and McRae, 1998; De Sousa-Vieira and

Milligan, 1999).

For example, Jackson and McRae (1998) con-

cluded that selecting families based on broad rather

than specific environmental adaptation was a more

productive breeding strategy in Australia. Milligan

(1994) reported that the number of final testing sites in

the Louisiana breeding program could be reduced

from 13 to 10 and still maintain 96% sucrose yield

repeatability. De Sousa-Vieira and Milligan (1999)

found that family � environment (environment-years)

variances had a minor effect on gains through

selection. However, Bull et al. (1992) concluded that

G � E interaction was large enough to reduce gains

made from selection at a central experiment station.

Mirzawan et al. (1994) tested G � E interaction

repeatability in Australia, and found that each

environment generated a different pattern of discri-

mination among the cultivars.

While G � E interactions have been studied

primarily as a decision aid for the design of sugarcane

breeding programs, less information has been pub-

lished in the scientific literature on G � E interactions

of released commercial sugarcane germplasm. In

Mauritius, Julien and Delaveau (1977) examined

sugarcane dry matter and sucrose content at three

dates of harvest for three varieties in four locations.

Partitioning of dry matter was affected more by date of

harvest and cultivar than by location. Chang (1996)

studied brix, purity and sugar content for six cultivars

grown at six locations for three crop years in Taiwan.

The G � E and G � E � year interactions were

significant for brix and sugar content, but not for

purity.

In Australia, Ellis et al. (2001) used district level

mill production data to examine sugarcane productiv-

ity trends over a 38-year period. The G � E interaction

term accounted for 4% of total variation in TCH, 5%

of KST and 7% of TSH. Cultivars performed well in

the first few years following release but poorly in late

ratoons. The authors noted that aggregated production

data confounded variety performance with other

factors. Ellis et al. (2004) also compared variety

trials to commercial production data in Australia.

Anomalies in ranking between data sets were

attributed to uneven deployment of clones in

commercial fields. Released variety trials have been

conducted in South Africa since 1966 (Redshaw,

2000) to produce varietal recommendation domains

for growers.

The examination of the significance of environment,

genotype and G � E interaction in recently released

germplasm is important both for grower choice of

cultivars and for verification of breeding program

results. In addition, since breeding programs often lack

the resources to allow replanting of the same cultivars at

the same location (Brown and Glaz, 2001), data sets in

which environment, crop age and year are not

confounded are often limited or simply not available.

Since the south Florida harvest season extends over

a 5-month period, it is also important to examine

trends of sucrose accumulation and yield over time as

well as space, as sugarcane harvested prior to

physiological maturity will not have reached peak

sucrose content (Miller and James, 1977; Gilbert et al.,

2004).

The objective of this experiment was to determine

the effect of genotype, environment, time of harvest

and their interactions on sucrose content and yield in

commercial sugarcane germplasm. Three non-con-

founded data sets (termed ‘‘case studies’’) were

examined separately to strengthen the inference base

for the analysis. While agronomic studies usually

report the results of a single experiment, the

magnitude of data collected in this project allowed

for the analysis of a total of three separate experi-

mental data sets. Each data set was non-confounded

R.A. Gilbert et al. / Field Crops Research 95 (2006) 156–170158

with respect to environment (different locations

within any given case study employ the same

year, crop age, cultivars, and biweekly harvest

periods). We chose to use all available data (three

data sets rather than one) to strengthen the inference

base for the analysis. This approach allowed us to

determine if the environmental effect on sugarcane

growth and its interaction with genotype and time of

harvest were consistent across different experimental

conditions.

2. Materials and methods

The trial was conducted in Florida at five locations

(some locations were repeated in different years)

across two different cropping seasons (Table 1). The

data analyzed for this experiment was part of a larger

cultivar � time sucrose accumulation trial (Gilbert

et al., 2004). From the larger data set, it was possible to

construct a total of three unique data sets (case studies)

to examine the non-confounded effect of environment

in each case study. The same year, crop age, cultivars

and sampling times were used for the different

environments in each case study. The effects of year

and crop age were thus not included in the statistical

analysis. The EREC environment was located at

268390N, 808380W, with a Lauderhill muck (euic,

hyperthermic Lithic Haplosaprist) soil type. The

Hillsboro environment was located at 268310N,

808280W, also with a Lauderhill muck soil. The

Lakeview environment was located at 268480N,

808410W, with a Torry muck (euic, hyperthermic,

Typic Haplosaprist) soil type. This environment is

Table 1

The three case studies

Case study Planting date Locations Year Cr

1 9 September 1997 Lakeview 1999/2000 Fir

21 November 1997 Hundley

8 January 1998 EREC

2 19 December 2000 EREC 2001/2002 Pla

31 October 2000 Hillsboro

3 16 November 1999 Hundley 2001/2002 Fir

31 August 1999 Lakeview

21 December 1999 Sundance

Within a given case study, calendar year, crop age, cultivar and sampling

regarded as ‘‘warmland muck’’ due to its proximity to

Lake Okeechobee. The lake effect reduces the risk of

freezes at this site. None of the cropping seasons

included in this study included a freeze event. The soil

at the Lakeview site also has a higher mineral content

(68–75%) than the other sites (20–48%). The Hundley

site was located at 268410N, 808270W, with a Lauderhill

muck soil. The Sundance site was located at 268360N,

808520W, also with a Lauderhill muck soil. The

Sundance environment is a ‘‘transitional area’’ with

higher sand content than the other Histosols included in

this study.

Cultivars included in this study, from the ‘‘CP’’

breeding program at Canal Point, FL, were released

from 1977 to 1996. They comprised > 78% of the

Florida sugarcane acreage in 2003 (Table 2), and were

thus representative of the range of commercial

germplasm used in Florida.

All experiments were planted in a randomized

block design using three or four replications with

cultivar as the main treatment. Table 1 lists the

planting date for each site. All sites were mechanically

harvested in mid-March of each year. Each plot was 4

rows wide by 10.7 m long with 1.5 m row spacing.

Plant populations were determined by whole-plot stalk

counts performed in July or August of each season.

Millable stalks with significant diameter at observer

breast height are normally counted during July and

August in Florida when stalk population has

stabilized, and lodging from tropical storms has not

yet occurred. Five-stalk plant samples were harvested

from each plot on 11 occasions roughly at 2-week

intervals starting from October 14. Sampling dates

were grouped by 2-week intervals (biweeks). Biweek

op age Cultivars

st ratoon CP 70-1133, CP 72-1210, CP 72-2086, CP 80-1743,

CP 80-1827, CP 88-1508, CP 88-1762, CP 89-2143

nt CP 72-2086, CP 78-1628, CP 80-1743, CP 84-1198,

CP 85-1382, CP 88-1762, CP 89-2143, CP 89-2377

st ratoon CP 72-2086, CP 80-1743, CP 84-1198, CP 85-1382,

CP 88-1762, CP 88-1834, CP 89-2143, CP 89-2377

dates were consistent across different environments (locations).


Table 2

Commercial cultivars included in the three case studies including year of commercial release, Crop Science registration reference, percent of

Florida 2003 acreage and sucrose yield as percent of check when released

Cultivar Year released Crop Sci. Reference 2003 FL areaa (%) TSH yield (%) (check)

CP 70-1133 1977 1978, 18:526 1.1 136 (CP 63-588)

CP 72-1210 1980 1981, 21:797 <1.0 125 (CP 63-588)

CP 72-2086 1982 1984, 24:210 9.1 113 (CP 63-588)

CP 78-1628 1989 1991, 31:236 12.3 91 (CP 70-1133)

CP 80-1743 1989 1991, 31:235 28.7 88 (CP 70-1133)

CP 80-1827 1987 1990, 30:232 <1.0 106 (CP 70-1133)

CP 84-1198 1992 1994, 34:1404 4.8 100 (CP 70-1133)

CP 85-1382 1993 1995, 35:1214 <1.0 109 (CP 70-1133)

CP 88-1508 1995 1997, 37:1387 <1.0 106 (CP 70-1133)

CP 88-1762 1995 1997, 37:1388 11.4 100 (CP 70-1133)

CP 88-1834 1996 2000, 40:576 <1.0 105 (CP 70-1133)

CP 89-2143 1996 2000, 40:577 10.7 117 (CP 70-1133)

CP 89-2377 1996 2000, 40:577 <1.0 107 (CP 70-1133)

a Glaz and Vonderwell (2004).

1 was October 14–October 27, biweek 2 (October 28–

November 10), biweek 3 (November 11–November

24), biweek 4 (November 25–December 8), biweek 5

(December 9–December 22), biweek 6 (December

23–January 6), biweek 7 (January 7–January 20),

biweek 8 (January 21–February 3), biweek 9

(February 4–February 17), biweek 10 (February 18–

March 3) and biweek 11 (March 4–March 17). For

Case Study 2, inclement weather and logistical

difficulties prevented sampling events during biweeks

1, 4 and 5.

Harvested sugarcane samples were topped in the

field, and millable fresh stalk weight was recorded.

Plant fresh weights were used to determine individual

stalk weight (kg stalk�1), and tons of cane per hectare

(TCH, t ha�1) were calculated as the product of stalk

number and stalk weight. To determine sucrose

concentration (KST, kg sucrose t�1), the harvest

samples were ground and the crusher juice analyzed

for Brix and pol. Brix, a measure of % soluble solids,

was measured using a refractometer which automa-

tically corrected for temperature (Meade, 1963). Pol, a

unitless measure of the polarization of the sugar

solution, was measured using a saccharimeter. Sucrose

yield (TSH, t sucrose ha�1) was calculated as the

product of TCH and KST (divided by 1000 to convert

kg sucrose to metric tons). A theoretical economic

index (EI, US$ ha�1) was also calculated which takes

into account harvesting, transport and milling costs

associated with TCH (Deren et al., 1995). This index is

not an exact measure of grower profits but rather a

method to rank genotypes based on economic criteria.

Repeated measures analysis of variance (Littell et al.,

2002) using SAS1 was performed to determine the

significance of the main effects of genotype, environ-

ment, and time, and the interaction of environ-

ment � time and genotype � environment. The proc

mixed procedure in SAS was used to perform the

repeated measures ANOVA. The covariance model for

each analysis was chosen based on procedures

outlined by Littell et al. (2002, pp. 281–285). The

interaction of genotype � time was analyzed sepa-

rately (Gilbert et al., 2004).

Paired t-tests were performed using least square

means estimates in SAS1 (Littell et al., 2002) to

contrast each pair of treatment means individually for

all effects. Due to space limitations, these pairwise

contrasts are discussed in the text, but are not

presented in tables. Instead, the least significant

difference at P = 0.05 (LSD.05) value is presented.

Cultivar KST, TCH and TSH rankings between

environments were correlated for the genoty-

pe � environment interaction means using Spear-

man’s rank correlation coefficient (rs):

rs ¼ 1 � 6X

d2� �

=ðn3 � nÞ (1)

where d is the difference in the rank of a given cultivar

between two environments, n the number of cultivars

in common between two environments.


Where noted, statistical significance refers to

P < 0.05 (*), P < 0.01 (**) and P < 0.001 (***) levels.

3. Results

3.1. Environment

The effect of environment was significant

(P < 0.01) on KST, TCH and TSH in all three Case

Studies (Table 3). Due to the extremely large F-test

values (Table 3) for the main effects of environment

(F-test range 26–104; mean 58.2), time (5.4–409;

111), and genotype (0.6–74; 19.6) relative to the

interaction terms of environment � time (1.04–38;

10.6) and genotype � environment (1.97–19.7; 6.77)

both main effects and interaction terms are discussed

when statistically significant. Three-way interactions

Table 3

Repeated measures ANOVA results for KST, TCH and TSHa for the thre

Case Study 1 C

DF F-test D

KST

Environment (E) 2 26.1***

Time (T) 10 311***

Genotype (G) 7 21.7***

Rep 2 2.65 NS

E � T 20 7.45***

G � E 14 4.31***

G � E � T 140 1.02 NS 4

TCH


Time (T) 10 13.8***

Genotype (G) 7 0.70 NS

Rep 2 7.06**

E � T 20 1.42 NS

G � E 14 2.57*

G � E � T 140 1.15 NS 4

TSH


Time (T) 10 90.3***

Genotype (G) 7 0.64 NS

Rep 2 4.67*

E � T 20 2.51***

G � E 14 1.97 NS

G � E � T 140 1.12 NS 4

a KST: kg sucrose t�1; TCH: t cane ha�1; TSH: t sucrose ha�1.* Indicates F-test significance at the P < 0.05 level.

** Indicates F-test significance at the P < 0.01 level.*** Indicates F-test significance at the P < 0.001 level.

of genotype � environment � time were not signifi-

cant (F-test range 0.69–1.54; mean 1.12) in the

majority of cases and are not discussed. In Case Study

1, the EREC site had significantly lower KST, TCH

and TSH compared to the Hundley and Lakeview sites

(Table 4). However, in Case Study 2, the EREC site

had significantly higher KST, TCH and TSH than the

Hillsboro site. The ranking of sites in Case Study 3 for

mean KST, TCH and TSH was Lakeview > Hundley

> Sundance.

In addition to higher soil mineral content, the

Lakeview site is distinguished by its location in the

‘‘warmland’’ muck area <1 km from Lake Okeecho-

bee. Air temperature data was not collected at all the

study sites, however 1999 and 2001 weather station

data from the University of Florida EREC (0.5 km

from the EREC test site) and the USDA-ARS

sugarcane field station at Canal Point (also <1 km

e case studies

ase Study 2 Case Study 3

F F-test DF F-test

1 53.9*** 2 104***

7 51.4*** 10 409***

7 26.1*** 7 74.1***

3 1.25 NS 3 6.17**

7 2.56* 20 6.35***

7 4.58** 14 19.7***

9 1.54* 140 1.27*

1 10.0** 2 91.0***

7 8.63*** 10 5.37***

7 16.2*** 7 4.23**

3 3.37* 3 0.90 NS

7 38.1*** 20 1.04 NS

7 7.92*** 14 4.65***

9 0.69 NS 140 1.11 NS

1 41.3*** 2 104***

7 24.0*** 10 89.6***

7 20.9*** 7 7.99***

3 4.11* 3 0.50 NS

7 33.1*** 20 2.91***

7 11.4*** 14 3.88***

9 0.98 NS 140 1.24*


Table 4

Sugarcane sucrose content, biomass yield, sucrose yield and economic index for the three case studies averaged by environment (location)

Location KST (kg sucrose t�1) TCH (t cane ha�1) TSH (t sucrose ha�1) EI (US$ ha�1)

Case Study 1

EREC 128 ca 87 b 11.2 b 1940 b

Hundley 136 a 124 a 16.9 a 3380 a

Lakeview 132 b 125 a 16.5 a 3230 a

Case Study 2

EREC 132 a 133 a 17.7 a 3510 a

Hillsboro 125 b 125 b 15.8 b 2930 b

Case Study 3

Hundley 131 b 136 b 18.0 b 3560 b

Lakeview 134 a 151 a 20.2 a 4140 a

Sundance 125 c 87 c 11.0 c 1900 c

a Means within a case study followed by the same letters are not significantly different (P < 0.05).

from Lake Okeechobee), document a 2.3–2.8%

warmer average annual temperature at Canal Point,

and a 7.0–8.8% higher average annual cumulative

thermal time (using a base temperature of 10 8C) at

Canal Point. Sugarcane leaf development and tonnage

is strongly influenced by temperature (Inman-Bamber,

1994; Bonnett, 1998; Sinclair et al., 2004) thus the

documented temperature differences are consistent

with the higher yields measured at Lakeview. High

yields at Lakeview also translated into higher

economic indices at this site (Table 4).

3.2. Time of harvest

Time of harvest is an important consideration in

commercial use of varieties. Given present milling

capacity in south Florida, a full 5 months are required

Table 5

Sucrose content by time of harvest (biweek) for all three case studies

Biweek Period Case Study 1 (kg sucrose t�1)

1 October 14–October 27 103

2 October 28–November 10 116

3 November 11–November 24 122

4 November 25–December 8 130

5 December 9–December 22 132

6 December 23–January 6 137

7 January 7–January 20 141

8 January 21–February 3 140

9 February 4–February 17 143

10 February 18–March 3 144

11 March 4–March 17 144

LSD.05 1.51

to process the 450,000 acres planted to sugarcane

(Saccharum spp.). Some sugarcane must be harvested

before achieving physiological maturity to sustain early

season (October–November) milling operations.

‘‘Early maturing’’ cultivars are preferentially harvested

during this time, recognizing that they may not have

reached their peak sucrose content, but may have higher

sucrose content than other later-maturing cultivars at

the onset of mill operations (Gilbert et al., 2004).

Time of harvest had a highly significant (P < 0.001)

effect on KST, TCH and TSH in all three case studies

(Table 3). KSTincreased significantly with each biweek

up to biweek 6 in Case Study 1 (Table 5). In Case Study

2, biweek 2 (the first sampling date for this case study)

and 3 had significantly lower KST than later harvest

periods. For Case Study 3, KSTwas significantly lower

in biweeks 1–5 than subsequent dates in 38 of 40

Case Study 2 (kg sucrose t�1) Case Study 3 (kg sucrose t�1)

– 100

117 113

124 125

– 130

– 135

132 136

131 137

134 140

133 141

132 140

127 136

1.82 1.34


Table 6

Sucrose yield and economic index by time of harvest (biweek) for all three case studies

Biweek Period Case Study 1

(t sucrose ha�1)

Case Study 2

(t sucrose ha�1)

Case Study 3

(t sucrose ha�1)

Case Study 1

(US$ ha�1)

Case Study 2

(US$ ha�1)

Case Study 3

(US$ ha�1)

1 October 14–October 27 10.5 – 12.2 1390 – 1630

2 October 28–November 10 12.4 14.5 13.5 1940 2470 2180

3 November 11–November 24 13.2 15.8 15.2 2300 2890 2810

4 November 25–December 8 14.7 – 16.3 2770 – 3170

5 December 9–December 22 15.6 – 17.1 3020 – 3430

6 December 23–January 6 15.7 17.8 17.4 3110 3520 3570

7 January 7–January 20 15.9 16.6 17.7 3250 3230 3640

8 January 21–February 3 15.2 17.1 17.5 3070 3410 3640

9 February 4–February 17 16.6 17.6 18.1 3450 3510 3790

10 February 18–March 3 16.9 16.9 18.0 3540 3300 3760

11 March 4–March 17 16.8 17.7 17.7 3510 3420 3590

LSD.05 0.62 0.52 0.67 190 140 170

pairwise mean comparisons (Table 5). Sugarcane

harvested in mid-October (biweek 1) had 29% lower

sucrose concentration (100–103 kg sucrose t�1) than

optimal harvest dates (141–144 kg sucrose t�1).

The trend of TSH over time followed a similar trend

to KST. In Case Study 1, sugarcane harvested from

biweeks 1–4 had significantly lower TSH (10.5–

14.7 t sucrose ha�1) in 33 of 34 pairwise contrasts

relative to later biweeks (15.2–16.9 t sucrose ha�1;

Table 6). Similarly, sugarcane harvested during biweeks

2 and 3 in Case Study 2 (14.5–15.8 t sucrose ha�1) and

biweeks 1–4 in Case Study 3 (12.2–16.3 t sucrose ha�1)

had significantly lower TSH than all subsequent

sampling dates (Table 6). Compared to time of optimum

TSH, harvesting sugarcane in mid- to late-October

resulted in yield reductions of 37% (Case Study 1), 18%

(Case Study 2) and 33% (Case Study 3). Economic

indices in mid-October were only 40% those in mid-

February (Table 6).

3.3. Genotype

The effect of genotype was highly significant

(P < 0.001) on KST in all three case studies (Table 3),

and significant (P < 0.01) on TCH and TSH in Case

Studies 2 and 3.

Across all three case studies, CP89-2143 consis-

tently averaged significantly greater KST (139–

144 kg sucrose t�1) than any other cultivar. Compared

to other cultivars, CP89-2143 KST was 7–13% greater

in Case Study 1, 2–12% greater in Case Study 2 and 5–

16% greater in Case Study 3.

In the two case studies including CP85-1382, the

cultivar consistently rankedat ornear the bottomofKST

responses. Although CP89-2143 KST was greatest

across all cultivars and case studies, CP88-1762 KST

was also favorably high in Case Study 1 (132 kg

sucrose t�1) and Case Study 3 (135 kg sucrose t�1).

CP72-2086 KST profiles were consistently high across

all three case studies, ranging from 133 to 136 kg

sucrose t�1.

TCH values were similar across cultivars in Case

Study 1. CP89-2377 and CP80-1743 had the highest

TCH levels that exceeded 140 t cane ha�1 in Case

Study 2. CP89-2377 is a high tonnage, low KST cultivar

(Gilbert et al., 2004). CP88-1762 and CP89-2143 were

the only cultivars approaching 140 t cane ha�1 in Case

Study 3, while CP85-1382 was notable for its poor TCH

(109–114 t cane ha�1) relative to other cultivars in both

Case Studies 2 and 3.

Although TSH for CP 89-2143 numerically

exceeded other cultivars, there were no significant

differences in pairwise comparisons of cultivar TSH in

Case Study 1 (Table 7). CP78-1628, CP89-2143 and

CP89-2377 all had TSH > 18.0 t sucrose ha�1 in Case

Study 2, which was significantly greater than CP85-

1382, CP72-2086 and CP84-1198 (Table 7). CP85-

1382 was notable for having the lowest TSH (13.4 t

sucrose ha�1) in Case Study 2. CP85-1382 (14.4 t

sucrose ha�1) and CP88-1834 (13.0 t sucrose ha�1)

had the lowest TSH in Case Study 3 (Table 7). In a

related study assessing cultivar sucrose accumulation

over time, CP85-1382 also performed poorly (Gilbert

et al., 2004). Economic indices of CP85-1382 were


Table 7

Sucrose yield and economic index by genotype for all three case studies

Cultivar Case Study 1

(t sucrose ha�1)

Case Study 2

(t sucrose ha�1)

Case Study 3

(t sucrose ha�1)

Case Study 1

(US$ ha�1)

Case Study 2

(US$ ha�1)

Case Study 3

(US$ ha�1)

CP 70-1133 15.1 – – 2840 – –

CP 72-1210 14.0 – – 2660 – –

CP 72-2086 15.0 14.7 15.8 2930 2900 3080

CP 78-1628 – 18.5 – – 3740 –

CP 80-1743 15.0 17.6 16.4 2710 3300 3240

CP 80-1827 14.6 – – 2780 – –

CP 84-1198 – 15.3 16.6 – 2780 3210

CP 85-1382 – 13.4 14.4 – 2370 2630

CP 88-1508 14.4 – – 2710 – –

CP 88-1762 14.7 17.8 18.9 2830 3420 3860

CP 88-1834 – – 13.0 – – 2290

CP 89-2143 16.0 18.4 19.7 3350 3820 4180

CP 89-2377 – 18.2 16.5 – 3430 3130

LSD.05 NS 0.88 1.55 380 190 360

only 63% those of CP89-2143, implying a severe

penalty to growers when using the wrong cultivar.

Recently released CP cultivars varied widely in

sucrose accumulation and yield. Superior sucrose

concentration is a favorable trait of CP89-2143, and

has been the main factor for the increase in CP89-2143

acreage in the EAA over the last few years (Glaz and

Vonderwell, 2004). Given the clear economic super-

iority of CP89-2143 to other cultivars (Table 7) its

acreage is likely to continue to increase. In the case of

CP89-2143 the pre-release breeding program data

(Table 2), variety trial data from this study (Table 7),

and commercial census data (Glaz and Vonderwell,

2004) are all indicative of its profitability. In contrast,

CP80-1743 is a profitable cultivar ranked #1 in Florida

sugarcane acreage, yet it performs poorly in small

plots (Tables 2 and 7).

3.4. Environment � time

The interaction of environment � time of harvest

was significant for KST and TSH in all three case

studies, but was not significant for TCH in Case

Studies 1 and 3 (Table 3).

The EREC site had particularly low KST early in

the season compared to other sites in Case Study 1.

Early season KST differences in Case Study 3 were

not significant in biweeks 1–2 between the Lakeview

and Sundance environments. However, Sundance KST

was significantly lower than both Lakeview and

Hundley at every sampling date beginning with

biweek 3.

TCH differences between environments were gen-

erally consistent across sampling times. Differences in

TCH between EREC and both Hundley and Lakeview

were highly significant on every sampling date in Case

Study 1, while Hundley and Lakeview TCH were never

significantly different in this case study. The EREC and

Hillsboro environment TCH were not significantly

different on 10 of 11 dates in the Case Study 2. The

Sundance environment had highly significant reduc-

tions in TCH compared to both Hundley and Lakeview

environments at every sampling date in Case Study 3.

TSH differences between sites also were generally

maintained across sampling times. EREC TSH was

significantly lower than Hundley and Lakeview

throughout the harvest season in Case Study 1. The

Sundance site in Case Study 3 had significantly lower

TSH than Hundley and Lakeview at every sampling

date. The Lakeview site was superior to Hundley on 10

of 11 dates in this case study.

3.5. Genotype � environment

The genotype � environment (G � E) interaction

term was significant for KST and TCH in all three case

studies, and for TSH in Case Studies 2 and 3 (Table 3).

Four of eight cultivars had non-significant differ-

ences in KST between environments in Case Study 1

(Fig. 1A). However, CP80-1743 and CP72-1210 had


Fig. 1. Genotype (Cultivar) � environment sucrose content (KST) means for (A) Case Study 1, (B) Case Study 2, and (C) Case Study 3.yDifferent letter indicates significant difference between locations for a given cultivar at P < 0.05 level. zNumber indicates cultivar rank at a

given location.


Fig. 2. Genotype (Cultivar) � environment biomass yield (TCH) means for (A) Case Study 1, (B) Case Study 2, and (C) Case Study 3. yDifferent

letter indicates significant difference between locations for a given cultivar at P < 0.05 level. zNumber indicates cultivar rank at a given location.


Fig. 3. Genotype (Cultivar) � environment sucrose yield (TSH) means for (A) Case Study 1, (B) Case Study 2, and (C) Case Study 3. yDifferent

letter indicates significant difference between locations for a given cultivar at P < 0.05 level. zNumber indicates cultivar rank at a given location.


highly significant differences in KST between

Hundley and EREC environments in this case study.

CP72-2086 and CP89-2143 had highly significant

differences in KST between environments in Case

Study 2 (Fig. 1B). CP84-1198 also had highly

significant differences in KST between Lakeview

and both Hundley and Sundance in Case Study 3

(Fig. 1C). CP72-2086 and CP88-1762 had stable KST

across environments in this case study.

The significant interaction terms for genotype �environment implies changes in cultivar ranking for

mean KST across environments. In Case Study 1,

CP72-1210 was ranked seventh in KST at EREC but

second in KST at Lakeview (Fig. 1A). Large shifts in

cultivar KST rank between environments also

occurred for CP80-1743 (Fig. 1B) and CP84-1198

(Fig. 1C).

In contrast, CP89-2143 maintained a remarkably

high, stable KST ranking across all three case studies.

CP89-2143 was ranked first in KST in 7 of the 8

environment-years, and second in one environment-

year (Fig. 1). CP89-2143 has clearly superior KST

compared to recently released CP cultivars across a

wide range of environments in the EAA.

The genotype � environment interaction term for

TCH was significant in all case studies (Table 3).

There were changes in cultivar TCH rank between

EREC, Hundley and Lakeview in Case Study 1

(Fig. 2A). For example, across all cultivars in Case

Study 1, CP88-1508 recorded both the lowest mean

TCH values (EREC) and highest mean TCH values

(Hundley and Lakeview; Fig. 2A). CP70-1133 and

CP80-1743 reflected the greatest stability (no sig-

nificant differences across sites) in TCH trends across

Case Study 1 environments. Although CP72-2086,

CP80-1743 and CP89-2143 recorded significantly

greater TCH at EREC than Hillsboro (Case Study 2;

Fig. 2B), the exact opposite trend was observed for

CP88-1762. In Case Study 3, CP88-1834 was notable

for its high TCH at Lakeview compared to Sundance,

although all cultivars recorded significantly lower

TCH values at Sundance compared to the other

environments in Case Study 3 (Fig. 2C).

Genotype � environment TSH was not significant

(P = 0.073; Table 3) for Case Study 1 (Fig. 3A). CP70-

1133 was the only cultivar not to have significant

differences in TSH between environments in this data

set. CP88-1508 and CP89-2143 had highly significant

reductions in TSH at EREC compared to the other

sites in Case Study 1. The genotype � environment

interaction term was significant for Case Studies 2 and

3 (Table 3). CP72-2086 and CP89-2143 had highly

significant increases in TSH at EREC compared to

Hillsboro (Fig. 3B). In contrast, CP88-1762 had

significantly greater TSH at Hillsboro (ranked first)

than EREC (ranked sixth). In Case Study 3 (Fig. 3C),

the three most recently released cultivars (CP88-1834,

CP89-2143 and CP89-2377) had the three highest

TSH ranks at the Lakeview site. CP88-1834 relative

performance was markedly better at Lakeview (ranked

third) than Hillsboro or Sundance (ranked last).

Spearman rank correlation coefficients (rs) were

significant (>0.83) between Hundley and Sundance

environments for KST and TSH in Case Study 3,

whereas rs was not significant (�0.17 to 0.28) in any

contrast with Lakeview in this case study. Even though

mean yield was closer between the Hundley and

Lakeview sites (Table 4), relative cultivar performance

was closer between Hundley and Sundance. A

significant negative correlation (�0.85) was found

between cultivar TSH rank at EREC versus Lakeview

in Case Study 1. This indicates that Lakeview is

located in a different agroecology than the other sites

included in this study.

4. Discussion

Our results highlight the influence of environment

on sugarcane yields in a visually homogenous region.

The EAA sugarcane production area is characterized

by flat basin topography, well-drained organic soils

with high N mineralization rates, and high to very high

organic matter contents (Bottcher and Izuno, 1994).

Unlike other sugarcane production areas in the world,

rainfall is not considered a limiting factor to sugarcane

production in the EAA due to the excellent water-

holding capacity of the organic soils and abundant

water supply from Lake Okeechobee (Alvarez et al.,

1982). TSH yields averaged over the same cultivars,

growing season, crop age and time of harvest varied

greatly from 2 to 46% among environments. In

contrast to the results of Julien and Delaveau (1977) in

Mauritius, this study supports arguments for multi-

locational evaluation of sugarcane germplasm in

Florida both during the breeding program and


following cultivar release. South Africa has had a

released variety trial program in place since 1966

(Redshaw, 2000) to recommend cultivars to growers in

different agroclimatic zones. Released variety trials

make inherent sense in S. Africa where 23 bioresource

regions have been identified in Kwa-Zulu Natal

province, and sugarcane production areas range from

loamy sandy soils in warm coastal areas to clayey soils

in cooler highlands. This study indicates that a similar

approach to released variety trials may be useful in

more homogenous regions.

Temporal trends in KST and TSH were consistent

with other investigations on older germplasm (Miller

and James, 1977; Rice, 1974) which found that

sugarcane harvested prior to mid-December in the

EAA will possess sub-optimal sucrose content.

Grower harvest strategies should include harvesting

cultivars with high ‘‘early season’’ sucrose levels

during October and November (Gilbert et al., 2004).

Cox et al. (1998) advocated a similar strategy to

increase grower gross returns in Australia. Both

selection and post-release trials should be harvested at

different stages of the season to identify such cultivars.

Although time of harvest had a significant effect on

TCH, there were no clear trends. One reason for this

complexity is that fresh weights, not dry weights, are

customarily measured for sugarcane. Crop fresh

weight may vary both over the season as plant relative

water content changes, and diurnally due to plant

stomatal activity (Liu and Helyar, 2003). Thus both

time of season and time of day affect fresh weight at

harvest. In addition, there is a direct relation in

repeated measures experiments between size of

individual samples and total plot size required. The

five-stalk samples used had higher variability in TCH

than KST, which may have been ameliorated by

increased number of stalks per sample. However

increasing sample size would have greatly increased

the resources required for land and labor to implement

these experiments.

It is interesting to note the extent of variation in

harvest traits of commercially released germplasm.

With the notable exception of CP89-2143, CP

cultivars have generally recorded yields within 10%

of the breeding program check in pre-release variety

trials (Table 2). However, across the case studies, KST

varied 13–18%, TCH 11-36%, and TSH 14–51%. Part

of this variability is due to genetic gain over time.

Edme et al. (2005) estimated that commercial sucrose

yield in the EAA had improved at the rate of

0.10 t sucrose ha�1 year�1 over a 33-yr period, 69%

of which was attributed to the CP breeding program.

However our current study indicates overall gain in

sugarcane yields will not translate into consistently

improved performance from each new cultivar.

Sucrose yields recorded by CP85-1382 and CP88-

1834 were inferior to earlier germplasm.

Sugarcane germplasm is released after numerous

years of replicated on-farm trials, yet considerable

variation in cultivar relative performance may be

expected following cultivar release. Many breeding

programs do not have the resources available to assess

cultivar performance following release. Relative

performance of new cultivars compared to industry

standards is often obtained ad hoc from mill managers

and industry professionals without replicated tests.

Ellis et al. (2004) compared variety trials to

commercial production in Australia, and reported

that differences in cultivar ranking between data sets

were due to uneven deployment of cultivars in

commercial fields. They concluded that variety trials

could not be enhanced to evaluate uneven deployment

effects. However, in S. Africa (Redshaw, 2000) post-

release variety trials have been used to recommend

varieties to growers. Our study indicates that a

systematic agronomic evaluation of released germ-

plasm is valuable in determining relative cultivar

performance and recommendation domains.

The environment � time of harvest interactions

indicate that relative differences in TSH between

environments at the beginning of the harvest season

are unlikely to change, whereas relative differences in

KST between environments may shift during the first

4–6 weeks of the harvest season. KST appears to

fluctuate both over time and space in the first 2 months

of the harvest season. Changes in KST should be

monitored across environments during the early

harvest period to ensure that the most profitable

environments are harvested during that time.

Significant G � E interactions indicated that the

Lakeview site was located in a different agroecolo-

gical zone than the other sites. Differences in soil

depth, mineral content and air temperature may

contribute to G � E interactions in the EAA. Lake-

view is <1 km from Lake Okeechobee in a ‘‘warm-

land’’ area, with soils containing appreciably greater


mineral content than the other sites included in this

study. Early breeding strategies in the EAA recog-

nized the importance of selection for both ‘‘warm-

land’’ sites and ‘‘coldland’’ sites further from Lake

Okeechobee (Bourne, 1972). Cultivars F31-962, F31-

436 and CL41-223 occupied over 50% of the EAA

acreage in the 1940–1960s, but faded from promi-

nence as sugarcane acreage spread further from the

lake. Rates of leaf appearance versus thermal time

differ among sugarcane cultivars (Bonnett, 1998;

Sinclair et al., 2004). Differing cultivar growth rates at

different cumulative thermal time may be part of the

mechanism involved in the G � E interaction of

‘‘warmland’’ versus ‘‘coldland’’ sites. Although the

CP program breeds new cultivars in a ‘‘warmland’’

environment adjacent to Lake Okeechobee, all

cultivars are tested in multiple ‘‘coldland’’ areas

and one ‘‘warmland’’ environment before cultivar

release. This data set indicates that a significant G � E

interaction still exists in many recently released

cultivars, with the recommendation domain of CP88-

1508 and CP88-1834 closer to Lake Okeechobee than

CP72-2086 or CP80-1743.

The vast majority of the scientific literature has

focused on the significance of G � E interactions for

breeding program design (Kang and Miller, 1984;

Glaz et al., 1985; Milligan et al., 1990; Bull et al.,

1992; Milligan, 1994; Mirzawan et al., 1994; Jackson

and McRae, 1998; Bissessur et al., 2000; Brown and

Glaz, 2001; Kimbeng et al., 2002). This study

indicates that significant G � E interactions persist

beyond cultivar release in commercially grown

germplasm. The high variation in sugarcane harvest

traits encountered in ‘‘elite’’ germplasm point to the

value of systematic agronomic monitoring following

cultivar release.

Acknowledgements

The authors gratefully acknowledge the assistance

of Mr. Robert Taylor, Mr. Matthew Duchrow, Mr.

Vincent Sampson and Mr. Henry Westcarth in sample

collection and processing. This research was sup-

ported by the Florida Agricultural Experiment Station

and a grant from the Sugar Cane Growers Cooperative

of Florida and approved for publication as Journal

Series No. R-10014.

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