Microbes as Biocontrol Agents: NEET MCQs with Answers

Explanation: Trichoderma species are free-living soil fungi that suppress several soil-borne plant pathogens and are therefore used as biological control agents.

Explanation: Trichoderma controls fungal plant pathogens, baculoviruses control insect pests and Bacillus thuringiensis controls caterpillars. Oscillatoria, Nostoc, Rhizobium and Azospirillum are biofertilizers.

Explanation: Insect hormones and pheromones are third-generation pesticides. Pheromones are chemical substances which, when released into the surroundings of an animal, influence the behaviour or development of other individuals of the same species. Inorganic substances, oils and plant extracts are first-generation and synthetic organic compounds second-generation pesticides.

Explanation: Paecilomyces lilacinus has proved effective for the biological control of nematodal disease in plants. It is easily produced in vitro and attacks the eggs of several nematode species, including root-knot nematodes and cyst nematodes.

Explanation: Trichoderma harzianum has an inhibitory effect on the growth of the mycelium of pathogens such as Pythium. By suppressing the growth of these fungi it allows the plant to grow favourably, and hence it is used for biological control of soil-borne plant pathogens.

Explanation: Xanthomonas campestris is itself the causative agent of a plant disease, black rot of cabbage, and hence is not a biopesticide. Bacillus thuringiensis, Trichoderma harzianum and NPV are all used as biopesticides.

Explanation: Bacillus thuringiensis is a Gram-positive, soil-dwelling bacterium used as an insecticide. It is an important reservoir of cry toxins and cry genes used for producing biological insecticides and insect-resistant genetically modified crops.

Explanation: Trichoderma is a free-living fungus used for foliar application, seed treatment and soil treatment to suppress various disease-causing plant pathogens.

Explanation: Trichoderma species are free-living fungi that act as effective biocontrol agents of several plant pathogens. Bt cotton is a genetically modified crop rather than a biocontrol application, and the lady bird beetle is an insect, not a microbe.

Explanation: Bacillus thuringiensis is a soil-dwelling bacterium used for the biocontrol of pest butterfly caterpillars. Its dried spores are mixed with water and sprayed on the plants; when eaten by the larvae the toxin is released in the gut and kills them.

Explanation: Baculoviruses attack insects and other arthropods; most of those used as biocontrol agents belong to the genus Nucleopolyhedrovirus. Trichoderma is used extensively against pathogenic fungi causing soil-borne diseases and Bacillus thuringiensis secretes toxin crystals that kill insect larvae. Rhizobium, Nostoc, Azospirillum and Oscillatoria are biofertilisers.

Explanation: Trichoderma species are free-living fungi that are very common in root ecosystems and act as effective biocontrol agents of several plant pathogens. Anabaena helps in nitrogen fixation, Lactobacillus in the production of lactic acid and Chlorella is a single-cell protein food supplement.

Explanation: A biocontrol agent used in an IPM programme must be species-specific and must have no negative impact on non-target organisms such as plants, mammals, birds, fish and other beneficial insects. It should kill only the targeted pest.

Explanation: Trichoderma is a microorganism applied against plant pathogens, which answers the question exactly. Bt cotton is a transgenic crop rather than an applied microbe, the ladybird is an insect and not a microbe, and baculoviruses attack insects rather than the fungus causing white rust.

Explanation: The fungus Paecilomyces lilacinus parasitises the eggs of root-knot and cyst nematodes and has proved effective for the biological control of nematode diseases in plants. Pisolithus is a mycorrhizal fungus.