Question

Microbes can be used to decrease the use of chemical fertilisers and pesticides. Explain how this can be accomplished.

Answer 1

1. Biocontrol-Biocontrol refers to the use of biological methods for controlling plant diseases and pests. In modern society, these problems have been tackled increasingly by the use of chemicals-insecticides and pesticides. These chemicals are toxic and extremely harmful to human beings and animals. Toxic chemicals reach the bodies of living beings through the food chain. They also pollute the environment.
2. Microbes as biofertilisers - The main sources of biofertilisers are bacteria, fungi and cyanobacteria. The nodules present on the roots of leguminous plants are formed by the symbiotic association of Rhizobium bacteria. These bacteria fix atmospheric nitrogen into organic forms, which are used by the plant as a 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. This relationship is called Mycorrhiza. Many members of the genus Glomus form mycorrhiza. In this relationship, the fungal symbionts absorb water and nutrients from the soil and provide them to the plants and obtain food from the plants.
   Cyanobacteria are autotrophic microbes which are widely found in aquatic and terrestrial atmosphere. Most of them increase the fertility of the soil by fixing atmospheric nitrogen in the form of nitrogenous compounds. For example - Anabaena, Nostoc, etc. Cyanobacteria play an important role as bio fertilisers in paddy fields.
3. Biological Control of Pests and Diseases - Our dependency on toxic chemicals and pesticides can be reduced to a great extent through biological control method. The bacteria Bacillus thuringiensis is used to control butterfly caterpillars. Because of the development of methods of genetic engineering in the last decade or so, scientists have introduced B. thuringiensis toxin genes into plants. Such plants are resistant to attack by insect pests. Bt-cotton is an example of this, which is being cultivated in some states of our country. Dragonflies, mosquitoes and aphids etc. are unable to harm Bt-cotton. The fungus Trichoderma is being developed as a biological control for the treatment of plant disease. It is an effective biological control agent for many plant pathogens. Baculoviruses are pathogens that attack insects and other arthropods. Most baculoviruses used as biological control agents are in the genus Nucleopolyhedrovirus. These viruses are best suited for species-specific, narrow-spectrum insecticide treatments.