Biological control

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Biological control

• Joyce E. Loper
• Research Plant Pathologist, USDA-Agricultural
  Research Service
• Professor (courtesy), Department of Botany and
  Plant Pathology
• loperj_at_science.oregonstate.edu
• 738-4057

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The Plant Disease Triangle
Take home message Microorganisms, whether
indigenous or introduced are an important
component of the environment.
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• 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.

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• 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.

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Biological Control of Plant Diseases
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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

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Suppressive Soils

• The pathogen does not establish or persist
• The pathogen establishes but causes little or no
  disease

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General Suppression
field soil
Disease severity
sterilized soil
Propagule level
A fixed level of the pathogen causes less disease
in the presence of indigenous soil organisms.
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Take all of wheat caused by Gaeumannomyces
graminis var tritici
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Take-all decline with monoculture of wheat
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Associating populations of organisms with soil
suppression
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Pseudomonas fluorescens produces an antibiotic
that is toxic to the take-all pathogen
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The antibiotic 2-4-diacetylphloroglucinol is
toxic to the take-all pathogen
O
O
O
H
C
H
C
H
3
3
O
H
O
H
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Wheat seed treatment with Pseudomonas fluorescens
for control of take-all
No seed treatment
Seed treatment with P.f.
Seed treatment with mutant that does not produce
an antibiotic
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Borneman and Becker evaluated the Microorganisms
associated with cysts in suppressive and
conducive soils
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Associating populations of organisms with soil
suppression
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Olatinwo, R., Borneman, J., and Becker, J. O.
2006. Induction of beetcyst nematode
suppressiveness by the fungi Dactylella
oviparasitica and Fusarium oxysporum in field
microplots. Phytopathology 96855-859.
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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
• Innudative mass introduction of biocontrol
  agent
• Crown gall
• Heterobasion root rot
• Fire blight
• Postharvest diseases

Chestnut Blight and hypovirulence
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• Biological control with Introduced Antagonists
• Biological control agent
• Hypovirulent isolates of Cryphonectria parasitica
• Disease Chestnut Blight
• Pathogen Cryphonectria parasitica
• Mechanism hypovirulence

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History of the Chestnut Blight Pathogen in the
United States
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Transmission of hypovirulence decreases with
diversity of vegetative compatibility groups in
the pathogen population
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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

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• Biological control with Introduced Antagonists
• Biological control agent
• Agrobacterium radiobacter
• Disease Crown gall
• Pathogen Agrobacterium tumefaciens
• Mechanism antibiosis

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Crown gall caused by Agrobacterium tumefaciens
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Infection by Agrobacterium tumefaciens
Short period of Susceptibility Wound
typically heals over after about 24 hours and is
no longer an opening for infection
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In nurseries growing woody perennials, wounds
are induced by root pruning. These can
be treated with the biocontrol agent immediately
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Untreated
Treated with K84
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• Why does biological control of crown gall
• work so well???
• Limited time of host susceptibility to disease
• This means the biocontrol agent doesnt
• have to persist for a long time in the
• environment
• The infection court is defined and easily treated
• This means the biocontrol agent can be
• applied directly to the infection court, and
  doesnt
• Have to move there on its own
• There are no chemical controls available
• The sensitivity of the pathogen population can be
  predicted
• For example, strains pathogenic to cherry are
• sensitive to agrocin 84, whereas strains
  pathogenic
• to apple are not uniformly sensitive.

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Kinds of Biological Control

• Conservation-
• 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

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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/jdeaco
n/microbes/heterob.htm
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• 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/jdeaco
n/microbes/heterob.htm
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• 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/jdeaco
n/microbes/heterob.htm http//www.nysaes.cornell.e
du/ent/biocontrol/pathogens/p_gigantea.html
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Kinds of Biological Control

• Conservation-
• 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

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• Decay management product
• for
• Citrus
• Stone fruits
• Pome fruits
• Potatoes

a.i. Pseudomonas syringae - ESC-10
EcoScience strain - ESC-11 USDA strain
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untreated
Bio-Save
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Why Postharvest Biocontrol?

• Market need
• few labeled chemicals
• fungicide resistance problem
• System characteristics

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Chlorine bath or spray
bin dump
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Clean Rinse or Fungicide Spray
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Wax application
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Bio-Save Application
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Usage History of Bio-Save by Crop
5,000,000
4,000,000
Cartons
3,000,000
2,000,000
Citrus
1,000,000
0
4,000,000
Potato
Cherry
8,000,000
3,000,000
6,000,000
Sacks
Lugs
2,000,000
4,000,000
1,000,000
2,000,000
0
0
1999
2000
2001
2002
2003
2004
2005
1999
2000
2001
2002
2003
2004
2005
From Stockwell and Slack. Phytopathology 97
244-249.
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Biological control
Not just a bug in a bag!
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The Plant Disease Triangle
Take home message Microorganisms, whether
indigenous or introduced are an important
component of the environment.