10. MICROBES IN HUMAN
WELFARE
5. MICROBES AS BIOCONTROL AGENTS
- 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.
6. MICROBES AS BIOFERTILISERS
·
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.
amazing notes thank you for this seriously
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