Write a note on heterosis.

Explanation

G.H.Shull in 1912 was the first scientist to use this term heterosis. This heterosis is the superiority of the `F_1` hybrid in performance over its parents. This is otherwise known as hybrid vigour. Increase in growth and crop yield, greater adaptability to resistance to disease, resistance to pest and droughy are the signs of hybrid vigour.
The best suited method for maintaining hybrid vigour is vegetative propagation because the desired characters are not lost over a period of time. The magnitude of heterosis is directly related to the degree of genetic diversity between two parents.