Tuesday, July 28, 2020

Microbes in Human Welfare - Notes | Class 12 | Part 3: Microbes as Biocontrol agents and Biofertilizers



-   Biocontrol is the use of biological methods for controlling plant diseases and pests. E.g. Lady bird (beetle) controls aphids. Dragon flies control mosquitoes.

-  Chemical pesticides and insecticides kill both useful and harmful organisms and cause pollution. Biocontrol method has no such problems.

Microbial biocontrol agents

o Bacillus thuringiensis (Bt): To control butterfly caterpillar.

   The dried spores of Bt (available in sachets) are mixed with water and sprayed on to vulnerable plants such as brassicas and fruit trees. These are eaten by the caterpillar. In their gut, the toxin is released and the larvae get killed.

   The scientists have introduced B. thuringiensis toxin genes into plants. E.g. Bt cotton.

o Trichoderma sp (fungus): These are free livings present in the root ecosystems. They control several plant pathogens.

o Baculoviruses (Especially genus Nucleopolyhedro-virus): Attacks insects and other arthropods.

It is suitable for species-specific, narrow spectrum insecticidal applications and desirable in IPM (Integrated Pest Management) program to conserve beneficial insects.


·   Biofertilisers are organisms that enrich nutrient quality of the soil. E.g. Bacteria, fungi, cyanobacteria etc.

·   Rhizobium (symbiotic bacteria in root nodules of leguminous plants) fix atmospheric N2.

·   Free-living bacteria in the soil (E.g. Azospirillum and Azotobacter) enrich the nitrogen content of the soil.

·   Mycorrhiza: Symbiotic association of fungi (E.g. genus of Glomus) with plants. The fungus gets food from plant.

The fungal symbiont performs the following:

o Absorb phosphorous from soil and passes it to the plant.

o Give resistance to root-borne pathogens and tolerance to salinity and draught.

o Give overall increase in plant growth and development.

·   Cyanobacteria (Blue green algae): Autotrophic microbes. They fix atmospheric nitrogen. E.g. Anabaena, Nostoc, Oscillatoria etc. In paddy fields, Cyanobacteria serve as an important biofertilisers. It also adds organic matter to the soil and increases its fertility.


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