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  • (a) Organic farmers prefer biological control of diseases and pests to the use of chemicals for the same purpose. Justify. (b) Give an example of a bacterium, a fungus and an insect that are used as biocontrol agents.   

(a) Organic farmers prefer biological control of diseases and pests to the use of chemicals for the same purpose. Justify.

(b) Give an example of a bacterium, a fungus and an insect that are used as biocontrol agents. 

 

 

 

 
 
 
 
 

Answers (1)

 a) The use of chemical fertilisers to meet the ever-increasing demand of agricultural produce has contributed significantly to pollution. There are problems associated with the overuse of chemical fertilisers and there is a large pressure to switch to organic farming – to use of biofertilisers. Biofertilisers are organisms that enrich the nutrient quality of the soil. The main sources of biofertilisers are bacteria, fungi and cyanobacteria. The nodules on the roots of leguminous plants formed by the symbiotic association of Rhizobium. These bacteria fix atmospheric nitrogen into organic forms, which is used by the plant as nutrient. Other bacteria can fix atmospheric nitrogen while free-living in the soil (examples Azospirillum and Azotobacter), thus enriching the nitrogen content of the soil.  

Fungi are also known to form symbiotic associations with plants (mycorrhiza).  The fungal symbiont in these associations absorbs phosphorus from soil and passes it to the plant. Plants having such associations show other benefits also, such as resistance to root-borne pathogens, tolerance to salinity and drought, and an overall increase in plant growth and development. 
Cyanobacteria are autotrophic microbes widely distributed in aquatic and terrestrial environments many of which can fix atmospheric nitrogen, e.g. Anabaena, Nostoc, Oscillatoria, etc. In paddy fields, cyanobacteria serve as an important biofertiliser.  Blue-green algae also add organic matter to the soil and increase its fertility. Currently, in our country, a number of biofertilisers are available commercially in the market and farmers use these regularly in their fields to replenish soil nutrients and to reduce dependence on chemical fertilisers. 
 
b) Biocontrol refers to the use of biological methods for controlling plant diseases and pests. This method relies on natural predation. 


Bacterium – Bacillus thuringiensis (Bt) is a bacterial Biocontrol agent that is used to control the caterpillars of butterflies. The dried spores of Bt are mixed with water and sprayed onto the plants. This toxin attacks the larval gut and kills them. 
 
Fungus – Trichoderma, a free-living fungus is used as a Biocontrol agent against numerous plant pathogens.  
 
Insect – Dragonflies are used to get rid of mosquitoes. A beetle, the ladybird is used to control aphids. 
 

Posted by

Priyanka Kumari

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