LIFE SCIENCE

Detailed explanation-1: -Azolla is water fern which is also used as a biofertilizer. There are around 80, 000 symbiotic cyanobacteria present on its leaves. Symbiotic cyanobacteria Anabaena Azollae is responsible for nitrogen-fixation which increases the fertility of the soil and in turn enhances the yield.

Detailed explanation-2: -Azolla is a floating pteridophyte, which contains as endosymbiont the nitrogen-fixing cyanobacterium Anabaena azollae (Nostocaceae family). Widely cultivated in the Asian regions, Azolla is either incorporated into the soil before rice transplanting or grown as a dual crop along with rice.

Detailed explanation-3: -So the correct answer is ‘Nostoc’.

Detailed explanation-4: -Note: As Azolla serves as a green fertilizer for almost all staple crop plants, it is chiefly used in the cultivation of Rice. The primary reason being, paddies or rice fields are one of the few places Azolla thrives and grows and provides nitrogen to the growing Rice.