What makes a compost disease suppressive? Allison L H Jack Dr. Eric B. Nelson’s Laboratory Group Veg Expo

Disease suppression… What do we know? Single organism biological control is well understood in specific cases Suppression of disease by a complex community of microbes is much more complicated!

Example: Pythium spp. (damping off) Post-emergence damping off [

A.Jack Cornell University 2008 vegetative hyphae sporangium germinating sporangium zoosporangiumzoospores antheridium oogonium oospore Germinating oospore asexual sexual direct indirect DISEASE [modified from Matthews 1931] P. aphanidermatum

Mechanisms of biocontrol Single organism: –Antibiosis –Competition for nutrients –Parasitism –Induced systemic resistance

Antibiosis Root surface Bacillus subtilis “Kodiak TM ” Zwittermicin A (antibiotic) [Shang et al. 1999] Pythium zoospore

Competition for nutrients Seed exudates Cucumber seed Linoleic acid Pythium sporangium [van Dijk and Nelson 2000] Enterobacter cloacae Linoleic acid Pythium sporangium

Induced Systemic Resistance (ISR) Pseudomonas corrugata Pythium sporangium [Chen et al. 2000]

Parasitism

Multiple organism biocontrol Often associated with high microbial biomass and activity, but not always Unclear which organisms are involved and how they interact with each other and the pathogen Goal: –Understand how disease suppression works in a single system so we can make the practice more effective

Effect of suppressive amendment on pathogen populations decrease null increase [Bonanomi et al 2010]

Microbiological Chemical Enzymatic Suppression Index (SI) If negative: negative correlation between factor measured and suppression If positive: positive correlation If zero: neutral [Bonanomi et al 2010]

Predictive factors vary by pathogen species

Thermophilic compost Static aerated (indoor) Windrows (outdoor) 6-9 months curing Relies primarily on action of microbes Vermicompost Usually follows a hot composting step Worm beds (indoor) Windrows (outdoor) Entire process: ~70 days What is vermicompost?

Vermicomposts can protect plants from disease Multiple cases documented in scientific literature But, suppression depends on: –Amendment rate –Type of feedstock –Temperature –Presence of synthetic fertilizers –Potting media substrate

Vermicompost is added to tops of plug trays, aerated vermicompost extract is piped directly into overhead irrigation 2008

Aerated compost extract Expensive equipment ($20,000) No shelf life Additives needed Cheap equipment ($250) Long shelf life No additives needed Non-aerated compost extract sump [Elzinga Hoeksema Nurseries, MI] 100 gallon tub Timer Sump pump (circulates 2x a day) 1:60 vermicompost: water ratio

Zoospore pre-infection events

Conclusions Vermicomposts can be a valuable cultural practice for suppressing plant disease Scientific understanding is not yet at a level where we can make predictions for specific composts and specific pathosystems Consider collaborating with regional researchers to further develop these practices

Acknowledgements Nelson Lab: Mary Ann Karp Eric Carr Monica Minson Hillary Davis Ellen Crocker Sarah Arnold Dave Moody My committee: Eric Nelson (PPPMB) Anthony Hay (MICRO) Anu Rangarajan (HORT) Kathie Hodge (PPPMB) Scott Peters (EDUC) Financial support: Department of Plant Pathology and Plant Microbe Biology USDA BARD Knight Institute for Writing in the Disciplines New York Farm Viability Institute NYSTAR Center for Advanced Technology & USDA SBIR Phase I & II (with Worm Power) Organic Farming Research Foundation Organic Crop Improvement Association Andrew W. Mellon Fellowship Kent Loeffler – photo credits SBIR Program Industry collaborator: Tom Herlihy Worm Power