Mixed species cover crops of winter rye and hairy vetch tended to increase tomato biomass and suppress plant diseases compared to single species cover crops. The study aimed to compare the effects of mixed and single species cover crops on tomato biomass and disease suppression. Preliminary results found that tomato plants grown in soil with previous mixed hay cover crops had higher fresh shoot biomass. Tomato plants from soil with a previous winter rye and hairy vetch mix also tended to show less disease symptoms, significantly in one-third of fields tested. Optimization of screening methods identified potential disease-suppressing bacteria in the plant rhizosphere.

1. Effects of mixed species cover
crop on tomato biomass and
plant disease suppression
Presenter: Emily Nguyen1
Brian B. McSpadden Gardener2 and Sun-Jeong Park2
Department of Biological Science, California State University
of Fullerton, Fullerton CA
Department of Plant Pathology, OARDC, The Ohio State
University, 1680 Madison Ave, Wooster OH
1

2. Introduction
• To get certified as organic farming, farmers can not
apply chemicals up to 3 years.
• Cover crops rotation can increase microbial diversity &
organic matter (Schonbeck and Morse, 2006).
• Benitez el al. (2009)
o Mixed hay soil increase tomato biomass & disease
suppression.
o Mitsuaria & Burkholderia, 2 novel biocontrol
bacteria were isolated from mixed hay soils.
2

3. Intro (cont.)
Cover
Crop
Planting
time
Mature
time
Benefits
Radish Early
Spring
Late
summer
NR= take up and holds soluble soil
nitrogen
B= harbors beneficial insects
TS= conditions, mellow top soil
Winter
Rye
Fall May NR= takes up and holds soluble soil
nitrogen
K= makes soil potassium more available
Hairy
Vetch
Early fall May N= fixed nitrogen
B= harbor beneficial insects
P= make soil phosphorous more available
3
Schonbeck and Morse (2006)
Table 1: Benefits of some cover crops to soil. Letters in bold indicate a strong effect.

4. 4
Winter Rye Hairy Vetch
Intro. (cont.)
Winter rye and hairy vetch cover crops were photographed in May, 2011.

5. Objectives and hypothesis
Objectives:
1) To compare effects of mixed vs. single species
cover crops on tomato biomass &
2) Compare effects of mixed vs. single species on
plant disease suppression
3) To isolate bacteria associated with plant disease
suppression & mixed species cover crops.
Hypothesis:
Mixed cover crops contribute to higher tomato
biomass and less disease symptom than single
cover crops.
5

6. Methods
6
Experimental Design
Randomized Complete Block
Mixed Hay, Rye+Vetch
Radish, Rye, & Vetch
East Badger, Fry (compost),
& Fry A
1) Soil fertility test
% organic matter & P
2) Fresh shoot biomass
above ground shoot
weight
3) Bacteria collection
~ 8000 bacteria isolates from
rhizosphere (1/2 R2A, ½ R2A+ Root
extract, 1/3 King’s Medium B, &
Leptothrix strain
Whole cell PCR
Pathogen
inoculation
108 Xanthomonas
cells/ml on 1
leaflet

7. 7
Fig. 1: % Organic Matter
Results_ Soil fertility
No significant difference of cover crops on % organic matter

8. 8
Fig. 2: Extractable Phosphate analysis from soil
Results_ Soil fertility
No significant difference of cover crops on P

9. Results_ fresh shoot weight
Fig. 3: Fresh shoot tomato biomass in July, 2011.
Field
Cover Crop
FryA
F
ry
East
Badg
er
Vetch
Rye
Vetch
R
ye
R
adish
M
ixed
h
ay
Vetch
Rye
Vetch
R
ye
R
adish
M
ixed
h
ay
Vetch
Rye
Vetch
R
ye
R
adish
M
ixed
h
ay
1800
1600
1400
1200
1000
800
600
400
200
Freshshootbiomass,g
9Plants from mixed hay soil have more fresh shoot weight

10. Results_ % disease symptoms
10
Fig. 4: Ranking score of percentage disease symptoms
Less disease symptom plants from rye + vetch soil,
significantly 1/3 fields

11. 11
NC
WC PC
DNA PC
DNA PC
WC PC
Mitsuaria_H24L5 Burkholderia_R2F4
Samples spiked with 6ul
of R2F4 DNA
100bp L
~450 bp
500
400
Fig. 5: Optimization of Mitsuaria and Burkholderia screening PCR.
Results_ Double freeze/thaw whole cell PCR
Burkholderia side, bands matched with positive control band
Successful double freeze/thaw screening method

12. Conclusion
• Tomato plants from mixed species of hay tended to
have more fresh shoot biomass.
• Tomato plants from rye + vetch tended to show less
disease symptom, significantly in 1/3fields.
• Double freeze-thaw has been successfully optimized
to screen for Mitsuaria and Burkholderia PCR.
12

13. Future Study
Screen and identify potential bacteria isolates
using a sequence marker following the method
of Benitez et al. (2009).
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14. Literature Cited
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.
3) Pal, K. K., and B. B. McSpadden Gardener. 2006. Biological Control of Plant Pathogen.
The Plant Health Instructor DOI: 10.1094/PHI-A-2006-1117-02.
4) Schonbeck, M., and Morse, R. 2006. Cover Crops for all Seasons: Expanding the cover
crop tool box for organic vegetable producers. Virginia Association for Biological Farming
Information Sheet.
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15. Acknowledgements
• Funding to support the development of these materials
was provided by the USDA’s Organic Agriculture
Research and Extension Initiative Grant 2009-51300-
05512.
• Many thanks to Summer Research Opportunity Program
at the Ohio State University
• Special thanks to Chunxue Cao, Xiaoqing Rong,
Veronica Cepeda and Matthew Worth for assisting with
field works.
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16. McSpadden Gardener’s Lab Members
Summer 2011
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Thank You!