NCERT-NEET-MICROBES AS BIOCONTROL AGENTS and AS BIOFERTILISERS

Aspect	Description
Biocontrol Definition	Biocontrol involves using biological methods to control plant diseases and pests. This approach contrasts with conventional methods that rely on toxic chemicals like insecticides and pesticides.
Environmental Impact of Chemicals	Chemicals used in conventional farming are harmful to humans, animals, and the environment, leading to soil and groundwater pollution and contaminating food.
Biological Control Methods	Relies on natural predation rather than synthetic chemicals. Organic farming promotes biodiversity, maintaining pests at manageable levels through a balanced ecosystem.
Examples of Natural Predators	Ladybirds control aphids, and Dragonflies manage mosquito populations. These natural predators reduce the need for harmful chemicals.
Microbial Biocontrol	Bacillus thuringiensis (Bt) is used to control butterfly caterpillars. Bt spores are sprayed on plants, where they are ingested by larvae, releasing toxins that kill them without harming other insects.
Genetic Engineering	Bacillus thuringiensis toxin genes have been introduced into plants, like Bt-cotton, making them resistant to insect pests and reducing the need for chemical pesticides.
Fungal Biocontrol Agents	Trichoderma species are free-living fungi effective against plant pathogens. They naturally occur in root ecosystems, making them a sustainable biocontrol option.
Baculoviruses	Baculoviruses are another promising biocontrol tool. These viruses specifically target insects and arthropods, making them ideal for integrated pest management (IPM) programs. Nucleopolyhedrovirus, a type of Baculovirus, has shown great potential due to its species-specific action, which protects beneficial insects and avoids harming non-target species like mammals, birds, and fish. This targeted approach is particularly valuable in ecologically sensitive areas where maintaining biodiversity is crucial.
Conclusion	Using biocontrol agents like Bt, Trichoderma fungi, and Baculoviruses reduces reliance on harmful chemicals, supports biodiversity, and promotes sustainable agriculture.
Subtopic: Biotechnology in Agriculture and Bt Crops
Biotechnology and Pest-Resistant Plants	Biotechnology in agriculture has led to the development of pest-resistant plants, reducing the need for chemical pesticides. One significant advancement is the use of Bt toxin, a protein produced by the bacterium Bacillus thuringiensis (Bt). The gene responsible for this toxin has been cloned and expressed in various crops, creating what is known as a bio-pesticide. Examples include Bt cotton, Bt corn, rice, tomato, potato, and soybean.
Bacillus thuringiensis (Bt) Mechanism	Bacillus thuringiensis produces proteins toxic to specific insects like lepidopterans (e.g., tobacco budworm, armyworm), coleopterans (e.g., beetles), and dipterans (e.g., flies, mosquitoes). During a certain growth phase, B. thuringiensis forms protein crystals containing the insecticidal toxin. This toxin is initially inactive in the form of a protoxin. However, when ingested by an insect, the alkaline pH of the insect’s gut converts it into its active form. The active toxin binds to the midgut epithelial cells, creating pores that lead to cell swelling, lysis, and eventually, the insect’s death.
Specific Bt Toxin Genes in Crops	Specific Bt toxin genes, such as cryIAc, cryIIAb, and cryIAb, have been isolated from Bacillus thuringiensis and incorporated into various crops, like cotton. These genes are selected based on the crop and the targeted pest, as most Bt toxins are insect-group specific. For instance, cryIAc and cryIIAb target cotton bollworms, while cryIAb targets the corn borer.

Aspect	Description
Environmental Impact of Chemical Fertilisers	The use of chemical fertilisers to meet the ever-increasing demand for agricultural produce has significantly contributed to environmental pollution.
Shift to Organic Farming	There is growing pressure to switch to organic farming due to the problems associated with the overuse of chemical fertilisers. Biofertilisers are used as an alternative to enrich soil nutrient quality.
Biofertilisers	Biofertilisers are organisms that enrich the nutrient quality of the soil. The main sources of biofertilisers are bacteria, fungi, and cyanobacteria.
Bacterial Biofertilisers	Rhizobium forms nodules on the roots of leguminous plants, fixing atmospheric nitrogen into organic forms used by the plant. Other bacteria like Azospirillum and Azotobacter fix atmospheric nitrogen while free-living in the soil, enriching nitrogen content.
Fungal Biofertilisers	Fungi like Glomus form mycorrhiza, where the fungal symbiont absorbs phosphorus from the soil and transfers it to the plant. This association provides additional benefits such as resistance to root-borne pathogens and tolerance to salinity and drought.
Cyanobacterial Biofertilisers	Cyanobacteria, such as Anabaena, Nostoc, and Oscillatoria, fix atmospheric nitrogen and add organic matter to the soil, increasing its fertility. They are especially important in paddy fields.
Commercial Availability	A variety of biofertilisers are available commercially and are used regularly by farmers to replenish soil nutrients and reduce dependence on chemical fertilisers.