Question

Yield of rice is enhanced by
A. Azolla
B. Anabaena
C. Nostoc
D. Clostridium

Answer 1

Hint: Rice is a grass species called Oryza glaberrima and its seeds are used as a major cereal grain. Its yield is enhanced by a symbiotically living aquatic fern which fixes atmospheric nitrogen. This nitrogen is converted into ammonium or nitrates required by the rice plant to grow healthy.

Complete answer: Rice is one of the staple diet sources used as a cereal grain. It is the seed of the grass species and holds importance for its nutritional values. It is the third-highest agricultural commodity produced in large numbers. The rice yield is enhanced by a symbiotic relationship between an aquatic fern and a nitrogen-fixing bacteria. Anabaena is a nitrogen-fixing symbiotically living bacteria. It lives in close association with Azolla which is an aquatic fern. The Azolla grows like a mat under the soil and encloses the cells of Anabaena. The bacteria entraps the atmospheric nitrogen and converts it into ammonium or nitrates. In return, they get home in the aquatic fern. The products of nitrogen fixation are used by the rice plant for their growth and development. These products enhance the development of seeds and thus, resulting in high yield. Azolla is used as green manure for its symbiotic properties with nitrogen-fixing bacteria and is produced commercially for agricultural practices. It is a potent biofertilizer. A biofertilizer is a living culture of useful bacteria that is applied to a crop for its enhancement.
Hence, the correct answer is option A.

Note: Various other symbiotically living nitrogen-fixing bacteria like Rhizobium are also used as biofertilizers. Flower bloom, seed production, increase in height are all enhanced by biofertilizers. Also, they are $100%$ organic and increase soil fertility without harming other organisms. An additional benefit of biofertilizers is they also protect plants from pathogenic bacteria.