Hybridization in plant breeding
India has several varieties of crops such as maize, tobacco, tomato,
potato and brinjal which were introduced from countries such as America, China and Australia. Introduced varieties sometimes do not get adjusted easily with our local environment.
It takes some time for these introduced crops to settle. Sometimes, it is essential to select suitable and desirable variety from the introduced plants. For example, a mung Phaseolus mungo variety was introduced from China but was not giving good yield and produced dull coloured seeds. From amongst the introduced mung crop, a plant suddenly produced large and bright coloured seeds.
This aspect may be due to sudden mutation. This variant plant was selected and further subjected to inter or intra specific crosses with our native crop. In this way, new varieties were produced and released as newly developed mung variety. Such a mung No.1 variety is now being cultivated in Punjab.
Hybridization is a method in plant breeding to improve the native crops by obtaining diverse genotypes that can be used as a source material for collection of crop with desirable characters and genes obtained from many parts of the world.
It involves crossing of two varieties or species or genera having desirable genes and breeding them together of the desirable traits into one progeny, which is called the hybrid. Hybrids are the products of first generation obtained by crossing genetically unrelated parents. When two individuals of the same species are crossed, it is called inbreeding or selfing or self-pollination.
This results in the increase of homozygosity. Particularly homozygous recessive alleles develop loss of vigor in plants. By careful observation of morphological features, we can remove these deleterious and harmful alleles by selection.
Protoplasmic fusion or somatic hybridization
A hybrid produced from fusion of protoplasts of two different species is called somatic hybridization. Naked protoplasts are obtained through dissolution of their cell walls by the macerating enzymes such as pectinase and cellulase.
Fusion of protoplasts from two different varieties can be enhanced by treatment with the chemical called polyethylene glycol (PEG) in the presence of high voltage electric current on a suitable medium.
By this method somatic hybrid plants with desirable changes can be obtained.
This method in plant breeding is called protoplasmic fusion. This concept
had been studied by you already in the chapter four.
The superiority of the F1 hybrid in performance over its parents is called heterosis or hybrid vigour. Vigour refers to increase in growth, yield, resistance to diseases, pests and drought.
F1 hybrids of maize show 25% increase in yield when compared to their own parent crop. 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.