Question

Write a note on heterosis.

Answer 1

The superiority of the F₁ hybrid in performance over its parents is called heterosis or hybrid vigour. Vigour refers to an increase in growth, yield, greater adaptability of resistance to diseases, pest and drought. Vegetative propagation is the best-suited measure for maintaining hybrid vigour since the desired characters are not lost and can persist over a period of time. Many breeders believe that its magnitude of heterosis is directly related to the degree of genetic diversity between the two parents. Depending on nature, origin, adaptability and reproducing ability heterosis can be classified as:

1. Euheterosis- This is the true heterosis that is inherited and is further classified as
2. Mutational Euheterosis – The simplest type of euheterosis and results from the sheltering or eliminating of the deleterious, unfavourable often lethal, recessive, mutant genes by their adaptively superior dominant alleles in cross-pollinated crops.
3. Balanced Euheterosis – Well balanced gene combinations which are more adaptive to environmental conditions and agricultural usefulness.
4. Pseudoheterosis – Also termed as luxuriance. Progeny possesses superiority over parents in vegetative growth but not in yield and adaptation, usually sterile or poorly fertile.