biological control
TRANSCRIPT
The Plant Disease Triangle
Path
ogen H
ost
Environment
Take home message: Microorganisms, whether indigenous or introduced are an important component of the environment.
Biological control
Reduction of the amount of inoculum or disease-producing activity of a
pathogen accomplished by or through one or more organisms
other than humans.
Biological control gained strength as a subdiscipline of Plant Pathology in the 1960s, when a group of scientists recognized that epidemics of soilborne plant diseases could not be understood without considering the the ecology of soil fungi and Oomycetes and the resident soil microflora.
Biological Control of Plant Diseases
Kinds of Biological Control
• Conservation- cultural practices Suppressive soils
General suppression
Specific suppression• Classical – self sustaining following a single release of a “natural enemy”
• Augmentative – periodic introduction to supplement natural reproduction Chestnut Blight and hypovirulence
• Innudative – mass introduction of biocontrol agent Crown gall Heterobasion root rot Fire blight Postharvest diseases
Suppressive Soils
• The pathogen does not establish or persist
• The pathogen establishes but causes little or no disease
General Suppression
A fixed level of the pathogen causes less disease in the presence of indigenous soil organisms.
Propagule level
Dis
ease
sev
erit
y
field soilsterilized soil
Take all of wheat caused by Gaeumannomyces graminis var tritici
Take-all decline with monoculture of wheat
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Years of Monoculture
Disease severity
Associating populations of organisms with soil suppression
Pseudomonas fluorescens produces an antibiotic that is toxic to the take-all pathogen
The antibiotic 2-4-diacetylphloroglucinol
is toxic to the take-all pathogen
CH3 CH3
OHOH
OHO O
No seed treatment Seed treatment with P.f.
Wheat seed treatment with Pseudomonas fluorescens for control of take-all
Seed treatment with mutant that does not produce an antibiotic
Borneman and Becker evaluated theMicroorganisms associated with cysts in suppressive and conducive soils
Associating populations of organisms with soil suppression
Olatinwo, R., Borneman, J., and Becker, J. O. 2006. Induction of beetcystnematode suppressiveness by the fungi Dactylella oviparasitica andFusarium oxysporum in field microplots. Phytopathology 96:855-859.
Kinds of Biological Control
• Conservation- cultural practices Suppressive soils
General suppressionSpecific suppression
• Classical – self sustaining following a single release of a “natural enemy”
• Augmentative – periodic introduction to supplement natural reproduction
Innudative – mass introduction of biocontrol agent Crown gall Heterobasion root rot Fire blight Postharvest diseases
Chestnut Blight and hypovirulence
Biological control with Introduced Antagonists
Biological control agent:
Hypovirulent isolates of Cryphonectria parasitica
Disease: Chestnut Blight
Pathogen: Cryphonectria parasitica
Mechanism: hypovirulence
History of the Chestnut Blight Pathogen in the United States
Transmission of hypovirulence decreases with diversity of vegetative compatibility groups in the pathogen population
Kinds of Biological Control
• Conservation- cultural practices Suppressive soils
General suppressionSpecific suppression
• Classical – self sustaining following a single release of a “natural enemy”
• Augmentative – periodic introduction to supplement natural reproduction Chestnut Blight and hypovirulence
• Innudative – mass introduction of biocontrol agent
Crown gall Heterobasion root rot Fire blight Postharvest diseases
Biological control with Introduced Antagonists
Biological control agent:
Agrobacterium radiobacter
Disease: Crown gall
Pathogen: Agrobacterium tumefaciens
Mechanism: antibiosis
Crown gall caused by
Agrobacterium tumefaciens
Infection byAgrobacteriumtumefaciens
Short period ofSusceptibility:Wound typicallyheals over after about 24 hours andis no longer an opening for infection
In nurseries growing woody perennials, wounds are inducedby root pruning. These can betreated with the biocontrol agent immediately
Treated with K84 Untreated
Why does biological control of crown gall work so well???
• Limited time of host susceptibility to disease This means the biocontrol agent doesn’t have to persist for a long time in the environment
• The infection court is defined and easily treatedThis means the biocontrol agent can be applied directly to the infection court, and doesn’tHave to move there on its own• There are no chemical controls available • The sensitivity of the pathogen population can be
predictedFor example, strains pathogenic to cherry are sensitive to agrocin 84, whereas strains pathogenic to apple are not uniformly sensitive.
Kinds of Biological Control
• Conservation- Suppressive soils
General suppressionSpecific suppression
• Classical – self sustaining following a single release of a “natural enemy”
• Augmentative – periodic introduction to supplement natural reproduction Chestnut Blight and hypovirulence
• Innudative – mass introduction of biocontrol agent Crown gall
Heterobasion root rot Fire blight Postharvest diseases
Heterobasidion root rot of pine
• The fungus Heterobasidion annosum is the most damaging root pathogen of coniferous trees in the Northern hemisphere.
• It progresses from the roots into the base of a tree, causing an economically important butt rot. • Once established in a site, the fungus is almost impossible to eradicate; it spreads
progressively by contact of healthy roots with infected roots
http://www.biology.ed.ac.uk/research/groups/jdeacon/microbes/heterob.htm
• Fruiting bodies release air-borne basidiospores that can spread the infection to new sites.
• Basidiospores land on freshly cut stump surfaces, and the fungus grows down through the stump tissues to the dead roots, from which it can infect the roots of adjacent healthy trees.
http://www.biology.ed.ac.uk/research/groups/jdeacon/microbes/heterob.htm
• Fresh pine stumps can be colonised by another fungus, Phlebiopsis gigantea (previously called Peniophora gigantea), which is weakly parasitic but poses no danger to healthy trees.
• If Phlebiopsis is applied first then it can prevent invasion by H. annosum, protecting the stump surfaces without the need for phytotoxic chemicals.
• P. gigantea is commercially available in Britain, Sweden, Norway, Switzerland and Finland, as either a spore suspension or a dry product (named "Rotstop").
• It was available in the USA until 1995 when the Environmental Protection Agency required it to be registered officially as a biological pesticide - a relatively expensive process that probably would not be cost-effective for the commercial producers.
http://www.biology.ed.ac.uk/research/groups/jdeacon/microbes/heterob.htmhttp://www.nysaes.cornell.edu/ent/biocontrol/pathogens/p_gigantea.html
Kinds of Biological Control
• Conservation- Suppressive soils
General suppressionSpecific suppression
• Classical – self sustaining following a single release of a “natural enemy”
• Augmentative – periodic introduction to supplement natural reproduction Chestnut Blight and hypovirulence
• Innudative – mass introduction of biocontrol agent Crown gall Heterobasion root rot Fire blight
Postharvest diseases
Decay management product
for • Citrus• Stone fruits• Pome fruits• Potatoes
a.i.: Pseudomonas syringae - ESC-10: EcoScience strain - ESC-11: USDA strain
Bio-Save
untreated
Why Postharvest Biocontrol?
• Market need:– few labeled chemicals– fungicide resistance problem
• System characteristics
bin dump
chlorine spray
Chlorine bath or spray
Clean Rinse or Fungicide Spray
fungicide in wax
Wax application
Bio-Save Application
Usage History of Bio-Save by Crop
0
1,000,000
2,000,000
3,000,000
4,000,000
5,000,000
Ca
rto
ns
Citrus
0
1,000,000
2,000,000
3,000,000
4,000,000
1999 2000 2001 2002 2003 2004 2005
Sa
cks
Potato
0
2,000,000
4,000,000
6,000,000
8,000,000
1999 2000 2001 2002 2003 2004 2005
Lug
s
Cherry
0
2,000,000
4,000,000
6,000,000
8,000,000
10,000,000
Ca
rto
ns
Pear and Apple
From Stockwell and Slack. Phytopathology 97: 244-249.
The Plant Disease Triangle
Path
ogen H
ost
Environment
Take home message: Microorganisms, whether indigenous or introduced are an important component of the environment.