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Biocontrol
Biocontrol: the use of microbes to control plant diseases or insects

Biological Control of Plant Diseases
A number of microbes have been used to control soil-borne and air-borne plant diseases
caused by plant pathogens as well as nematode pests
In some cases, good success have been achieved by biological control
- Not in all cases

Tactics of Biological Control
Two main approaches:
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Protection of introduced antagonists of fungi and bacteria

Eradication or Reduction of Inoculum
Under some situations, biocontrol can be used to reduce or eradicate pathogen inoculation
It is achieved through suppressive soils and hyperparasites
Several soil-borne pathogens e
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- Fusarium oxysporum (vascular wilt)
- Phytophthora cinnamomi (root rot of fruits and trees)
- Pythium sp
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g
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Antagonistic to Streptomyces
scabies (which cause potato scab disease)
Pasteurization of soil at 60 C for 30 min completely eliminates the suppressiveness of the soil

Hyperparasites
Hyperparasites: living organisms which parasitize other parasites
Hyperparasites provide an ideal organism for several soil-borne and aerial plant pathogens
Soil-borne pathogens can be reduced or eliminated by using hyperparasites both fungi and
bacteria
The mycelium & resting spores of several soil-borne pathogens e
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- Pythium
- Rhizoctonia
- Phytophthora
- Sclerotium
Are attacked by non-pathogenic fungi, bacteria and Actinomycetes
Fungal Hyperparasites
Hyperparasites

Target pathogens

Laetisaria arvalis

Rhizoctonia, Pythium

Sporodesmium sclerotivorum

Sclerotinia sclerotium and other species

Talaromyces flavus

Verticillium (wilt)

Pythium spp
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Pythium

Pichia guilliermondii

Botrytis, Penicillium

Trichoderma harzianum

Rhizoctonia, Sclerotium, Phytophthora,
Fusarium

Bacterial Hyperparasites
Bacteria

Target Pathogens

Bacillus

Sclerotiourum

Entrobacter

Phytophthora

Pseudomonas

Pythium

Nematode Hyperparasite

Target Pathogen

Aphelenchus avenae

Rhizoctonia

Aerial Hyperparasites
Hyperparasites

Target pathogens

Tuberculina maxima

Cronartium (pine rust)

Darluca filum
Verticillium lecanii

Several rusts

Ampelomyces quisqualis

Several powdery mildews

Tilletiopsis spp
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Protection by Introduction of Antagonistic Fungi & Bacteria
These are successful only for soil-borne pathogens so far
Success Story of Root-rot pathogen of Conifers:
- This disease has been successfully controlled by using fungal antagonist
- Cause of disease is: Heterobasidion annosum
- This pathogen attacks freshly cut pine trees and spread into roots
- The infected trees are inoculated with oidia of the antagonistic fungus Phiebiopsis
gigantea

Examples of Effective Control of Phyllosphere
Chestnut blight is caused by Cryphonectria parasitica and is controlled by hypovirulent strain of
the same fungus which carries ds RNA virus
Example of Bacteria:
- Crown gall disease of fruits caused by Agrobacterium tumefaciens and is controlled by
treating the seeds, cuttings and seedlings with “Galltrol”, a suppression strain of
non-pathogenic Agrobacterium radiobacter, it produces “Agrocin-84” which is
antagonistic

Microbial Pesticides (Biopesticides)
Viral biopesticides
Bacterial biopesticides
Fungal biopesticides
Microbial pesticide: preparations of antagonistic microbial populations used to control
microbial plant pathogens
Bacterial insecticides
- Bacillus thuringienesis (Bf) (a bacterium) is the most successful biocontrol agent which
has been used successfully as bioinsecticide against several insects
- Ex
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Regulatory
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Physical
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Biocontrol
Commercial Reality of Microbial Herbicides
It is easy to evaluate the effectiveness of a herbicide in vitro but under field conditions its
effectiveness is not as much as under laboratory conditions because it is difficult to control the
environmental factors that affect the effectiveness of a biocontrol agent
Biocontrol is more effective in Rhizosphere as compared to Phylloplane
For soil-borne pathogens, the formulations containing bacteria:
- Pseudomonas fluorescens
- Agrobacterium radiobacter
- Bacillus subtilus
Are most commonly used in USA
Pellet formulations of Gliocladium is used as biocontrol against plant diseases such as:
- Damping off [Pythium sp
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g
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Biodeterioration of agricultural products causes heavy losses annually
- About 20-30% average loss is caused due to post harvest diseases

Mycotoxins in Biodeterioration
Some fungi produce poisonous metabolites, known as mycotoxins
They induce death and also cause other toxic effects when contaminated feed/food is
consumed by animals and human beings
Ingestion of mycotoxins cause intoxication, termed as mycotoxicosis
More than 100 species of fungi have been reported to produce mycotoxins and these belong the
the genera:
- Aspergillus
- Penicillium
- Fusarium

Mycotoxins
Four groups of mycotoxins are considered to be associated with diseases in humans
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Ochratoxins
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Trichothecenes

Aflatoxins
Maize (corn) is often contaminated with aflatoxin up to 97%
Aflatoxins are also found in tree nuts, copra, and other species
The common fungi that produce aflatoxins are:
- Penicillium Islandicum
- A

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