What makes a compost disease suppressive?
Allison L H JackDr. Eric B. Nelson’s Laboratory Group
Veg Expo 1-27-10
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
[www.ipmimages.org]
A. Jack Cornell University 2008
vegetative hyphae
sporangium
germinating sporangium
zoosporangium zoospores
antheridium
oogonium
oogonium oospore
Germinatingoospore
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
www.nysaes.cornell.edu/ent/biocontrol/pathogens/trichoderma
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]
Mic
robi
olog
ical
Chem
ical
Enzy
mat
icSuppression 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
AcknowledgementsNelson Lab:Mary Ann KarpEric CarrMonica MinsonHillary DavisEllen CrockerSarah ArnoldDave 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