Hybridization

Hybridization

In traditional terms, hybridization refers to the union of the male and the female gamete to produce a zygote. In plant science, hybridization also refers to the crossing or mating of two plants. The story of scientific hybridization of crop plants started with J G Kolreuter, who in 1761 published his work on the scientific bases of hybridization. Since then, hybridization followed by selection, has been the major tool of plant breeding.

In his quest to find more variability, man started experimenting with hybridization of plants so as to achieve the perfect plant type. This process was actually the beginning of expedited evolution since it led to the formation of new plant types artificially or due to human  intervention at a much faster pace than it would have happened in nature. For example, the bread wheat that we eat today has taken about 500 years to evolve to its present form through human intervention. This form of wheat would have taken thousands of years to evolve had it been left to the natural evolution process.

Ways in which hybridization is used

Some of the ways in which hybridization has been exploited in breeding crop plants are given below

Combination breeding: The main aim of combination breeding is to transfer one or more characters into a single variety or plant type from many others.

For this, an existing plant variety may be used as the recipient parent while many other crop varieties or wild relatives may contribute as donor parents. The most commonly used method to achieve this goal is known as the backcross method. The plant type in which the character or the trait is being transferred is known as the recipient parent and the other as the donor parent. For this, the two plants are mated or crossed and the progeny is screened for the desired trait. The progeny plants possessing the desired trait are then selected and crossed back to the recipient parent. This process is repeated until the desired plant type having all the characteristics of the recipient in addition to the trait being transferred is finally obtained. This exercise is known as backcrossing. Backcrossing involves both hybridization and selection.

Hybrid varieties: Plant scientists exploit the characteristic feature of better yielding ‘hybrids’ in plants. Hybrid vigour, or hetrosis as it is scientifically known, exploits the fact that some offspring from the progeny of a cross between two known parents would be better than the parents themselves. Many hybrid varieties of several crop species are being grown all over the world today. An example of this is the hybrid tomatoes that we eat commonly. The philosophy of hybridization has been extended from ‘within the same species or genera (the same type of plants)’ to ‘different species or genera (totally different plants)’. This is known as wide or distant hybridization. Wide hybridization has helped breeders to break what is known as the species or genera barrier for gene transfer, i.e. it has helped breeders to transfer beneficial characteristics from wild and weedy plants to the cultivated crop species.

      
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