How many of the following statements about biofertilisers are correct?
A. Azospirillum and Azotobacter can fix atmospheric nitrogen while free-living in the soil.
B. Many members of the genus Rhizobium form mycorrhiza with the roots of plants.
C. Blue green algae add organic matter to the soil and increase its fertility.
D. Plants having mycorrhizal associations show resistance to root-borne pathogens.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Three
Biofertilisers are organisms that enrich the nutrient quality of the soil. The main sources are bacteria, fungi and cyanobacteria, and each group helps the plant in its own way.
A. Azospirillum and Azotobacter can fix atmospheric nitrogen while free-living in the soil. — True. These bacteria do not need a host plant. They fix nitrogen while living free in the soil and so enrich its nitrogen content.
B. Many members of the genus Rhizobium form mycorrhiza with the roots of plants. — False. Mycorrhiza is an association of a fungus with plant roots, and many members of the genus Glomus form it. Rhizobium is a bacterium that forms root nodules in leguminous plants and fixes nitrogen.
C. Blue green algae add organic matter to the soil and increase its fertility. — True. Cyanobacteria (blue green algae) such as Anabaena and Nostoc fix nitrogen and also add organic matter to the soil. They are an important biofertiliser in paddy fields.
D. Plants having mycorrhizal associations show resistance to root-borne pathogens. — True. Besides getting phosphorus from the fungus, such plants show resistance to root-borne pathogens, tolerance to salinity and drought, and better overall growth.
A, C and D are correct, so three statements are correct.
NCERT Extract:
Microbes as Biofertilisers – “… You have studied about 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). Many members of the genus Glomus form 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.”
Microbes as Biofertilisers – “… In paddy fields, cyanobacteria serve as an important biofertiliser. Blue green algae also add organic matter to the soil and increase its fertility.”