Question

Write short notes on
(a) Mycorrhiza,
(b) Role of VAM in crop improvement,
(c) Rhizobium-legume symbiosis,
(d) Green manure

Answer 1

Symbiosis is the mutual association between two organisms in which at least one of the species is benefitted. The association can be positive, negative or neutral. This type of interaction is close and prolonged and occurs between two different species.

Complete answer:
Mycorrhiza- It is a type of symbiosis which occurs between the fungus and the roots of the vascular plant. The plant provides the food and other nutrients obtained through photosynthesis whereas the fungi supply plants with the phosphorus which is essential for growth and development of the plant. Both the species are benefited by this association.

VAM- Vesicular Arbuscular Mycorrhiza is the symbiotic association between the fungi and the roots of angiosperm. The fungus forms vesicles and arbuscules in the root cortex and causes damage to the plant tissue. This association provides the plant with necessary strength to fight against diseases and also makes the soil fertile by supplementing phosphorus.

Rhizobium-legume symbiosis- It is the symbiotic relation between the rhizobium bacteria and the roots of the leguminous plants. It forms root nodules which help in fixing atmospheric free nitrogen and convert them into nitrates and nitrites. In turn, plants provide shelter and other nutrients needed by the bacterium.

Green manuring- It is the growing of the cover crop sown on agricultural land which help in fertilizing the soil by supplementing the nitrogen to the soil. It mainly includes the leguminous crops. It also helps in soil conservation.

Note: Green manuring is very useful for the plants as well as soil. It helps in improving the organic matter of the soil. It makes the soil arable. It provides food and energy to the microbes which help them to multiply rapidly. After the decomposition of these plants, the plant nutrients and other things are left to the soil which is utilised by the crops.