Effects of Mixed Species Cover Crop on Tomato Biomass and Plant Disease Suppression Emily Nguyen1, Sun-Jeong Park2 and Brian McSpadden Gardener2

1California State University of Fullerton, Fullerton CA2Department of Plant Pathology, OARDC, The Ohio State University, 1680 Madison Ave, Wooster OH

Results

No-weeding Herbicide No-weeding Herbicide

Literature Cited

AcknowledgementsFunding to support the development of these materials was provided by the

USDA's Organic Agriculture Research and Extension Initiative Grant 2009-

51300-05512 and SROP at the Ohio State University.

Conclusion

Future Study

AbstractThe benefits of cover crops are based on substrate-induced changes of soil

chemistry and biology. The study objectives are to compare the effects of mixed

and single species cover crops on plant disease suppression in organic tomatoes

and isolate diverse bacteria samples from tomato rhizophese, which were

screened for strains of Mitsuaria and Burkholderia as biocontrol inoculants with

cover crops for later disease plant management in organic farming. It is

hypothesized that tomatoes grown on mixed species cover crops will have a

higher biomass and show less disease symptoms than those grown on single

cover crops. Mixed of winter rye and hairy vetch, and mixed species of hay and

three single species of winter rye, hairy vetch, and tillage radish were compared

at separate locations in Wooster, OH. Tomato Foliage was inoculated with

bacterial pathogen, Xanthomonas euvasicatoria; percentage of disease foliage

was measured, at the flowering stage height and shoot biomass was measured.

We predict that tomatoes grown on mixed cover crops will have a higher

biomass and show less disease symptoms than those grown on single cover

crops. Tomato plants from mixed hay tended to have larger biomass; those from

rye vetch tended to have less disease symptoms. Double freeze-thaw was a

successful method to screen for Mitsuaria and Burkholderia

IntroductionFarmers are seeking alternative tools to manage their farm; and cover crop

strategy is one of the approaches. Such substrate-induced changes of soil

bacterial community may be linked to specific cover crop and plant disease

suppression. Suppression of plant disease under incorporation of cover crop in

crop rotation has been observed2. Rotating mixed species of hay prior to

growing tomato plants has been tested as a tool to increase yield and to control

plant disease2. Yet the specific bacteria and mechanism associated with such

cover crop has not been identified. This study aims to test whether mixed cover

crop can provide more added values to the organic vegetable farming and link to

beneficial soil bacteria that may contribute to soil borne plant disease

suppression.

HypothesisMixed cover crops contribute to higher tomato biomass and less disease

symptom than single cover crops.

• Randomized complete block design was used to compare mixed (mixed

species of hay and rye + vetch) and single species (radish, rye, and vetch)

cover crops at two separate locations in Wooster, OH. Fry was added compost.

• Bacterial pathogen Xanthomonas at 10^8 cells/ml rate was inoculated on one

leaflet and percentage of foliage developed disease symptom was measured.

• Tomato fresh shoot biomass was measure at flowering stage of the plants, late

July.

• ~ 8000 bacteria isolates were collected from tomato rhizosphere using four

media (1/2 R2A, ½ R2A with root extract, 1/3 King’s medium B and

Leptothrix strain media) at flowering stage, late July.

• Whole cell PCR method used to screen Mitsuaria and Burkholderia was

optimized.

Fig. 1: Fresh shoot tomato biomass in July, 2011.

Fig.1: Disease symptoms on tomato leaflets after being sprayed with

Xanthomonas, plant pathogen

Fig. 2: Percentage of leaf surface showed disease symptoms about a week after

the Xanthomonas inoculation.

1.Baysal, F., M. S. Benitez, M. D. Kleinhenz, S. A. Miller, and B. B. McSpadden

Gardener. 2008. Field management effects of damping-off and early season vigor of crops

in a transitional organic cropping system. Phytopathology 98:562-570.

2.Benitez, M. S., and B. B. McSpadden Gardener. 2009. Linking Sequences to Function

in Soil Bacteria: Sequence-Directed Isolation of Novel Bacteria Contributing to Soilborne

Plant Disease Suppresion. Appl. Environ. Microbiol. 75:915-924.

Methods

• Tomato plants from rye and vetch tended to be lower percent disease pressure

significant in one the three fields (Fig. 3).

•Tomatoes from East Badger tended to have higher percent disease pressure

than those from Fry and Fry A (Fig. 2).

•Tomato plants grown after mixed species of hay tended to have greater

biomass (Fig. 1). A diverse plant material from mixed hay cover crop might

have variable nutrient favorable for plant growth.

•Tomato plants grown following the rye + vetch cover crop tended to be lower

in percent disease pressure, significantly so in one of three fields (Fig. 3). A

greater amount of rye + vetch biomass added to the field may have been a

contributing factor for being more effective plant disease suppressor .

•Compost amendment on Fry had been a contributing factor to higher tomato

biomass and less disease pressure.

•Double freeze-thaw has been successful optimized to screen for Mitsuaria

and Burkholderia PCR.

•This method will be used to screen bacterial collection in the future.

Screen and identify potential bacterial biocontrol isolates using a sequence

marker following the method of Benitez et al. (2009).

L

• Repeated pattern of tomato plants having higher biomass grown after mixed hay

cover crop was observed all three locations.

Mixed hay > Radish > Vetch > Rye > Rye + Vetch

•There was no statistically significant difference among five cover crop treatments

on tomato biomass (p-value > 0.05).

•There was a significant field effect for tomato biomass. Tomato plants from Fry

having additional compost amendments had highest biomass followed by those

from Fry A and East Badger.

Fig. 3: Ranking score of percentage disease symptoms

Field

Cover Crop

FryAFry

East Badger

Vetch

Rye Vetc

hRye

Radish

Mix

ed hay

Vetch

Rye Vetc

hRye

Radish

Mix

ed hay

Vetch

Rye Vetc

hRye

Radish

Mix

ed hay

1800

1600

1400

1200

1000

800

600

400

200

Fres

h sh

oot

biom

ass,

g

Field

Cover Crop

FryAFry

East B

adger

Vetch

Rye Vetc

hRye

Radish

Mix

ed hay

Vetch

Rye Vetc

hRye

Radish

Mix

ed hay

Vetch

Rye Vetc

hRye

Radish

Mix

ed hay

40

35

30

25

20

15

10

5

% L

eafle

t su

rfac

e sh

owin

g di

seas

e sy

mpt

om

Fig. 4: Mitsuaria and Burkholderia optimization screening PCR. 12A DNA

sample was collected from 3 different media. Ladder (L), negative control (NC)

was PCR water, whole cell positive (WC+), and DNA positive control (DNA +).

•Burkholderia PCR side, bands with correct size resulted from the DNA spike.

There was no spiking on Mitsuaria PCR side.

•Double freeze-thaw method was working for both Mitsuaria and Burkholderia

whole cell PCR screening.

L LN

C

W

C

+

D

N

A

+

N

C

D

N

A

+

Burkholderia PCR

500400

MitsuariaPCR W

C

+100bp L

~450 bp