Method of Plant Breeding in Self Pollinated Plants – Back Cross Method

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Method of Plant Breeding in Self Pollinated Plants – Back Cross Method

Definition of Back Cross Method:

A cross between F1 hybrid and one of its parents is known as a backcross. It is proposed by Harian and Pope in 1922, as a method breeding for small grains and is employed in improvement of both hybrid.

In this method two plants are selected and crossed and hybrid successively backcross to one of their parents. As a result the grain hybrid backcross progeny becomes increasingly similar to that of the parents to which it identical with the parent used for backcrossing. In this method the desirable variety which are lacking in some characteristics known as a recurrent or recipient parent, while the undesirable variety on wild variety processing only one or two desirable characteristics known as donor parent or non recurrent parent. The objectives of this method are to improve one or two specific defects of high yielding variety.

For the successful development of a new variety, following requirements must be fulfilled.

1) A suitable recurrent parent must be available which  lack in one or two characters.
2) A suitable donor parent must be available which passes the characters be transfer in highly intense form.  
3) The character to be transferred much have high heritability.
4) A sufficient number of backcrossed should be made so that the genotype of the recurrent parent is recovered in full .
Application of the Backcross Method:

This method is commonly used for the transfer of disease resistant from one variety to another. But is also suitable for the transfer of quantitative characters and is applied is both self and cross pollinated crops.

1) Intervarietal transfer of simply inherit characters such as disease resistance , seed colour , plant height etc.
2) Intervarietal transfer or quantitative characters. Such as earliness, seed size, seed shape may be transferred from one variety to another belongings to same species.
3) Interspecific transfer of simply inherited characters i.e disease resistance from related species to cultivated species. Ex. Transfer of leaf and stem rust resistance from Triticum monococum to Triticum aestivum.
4) Transfer of cytoplasm from one variety or species to another and is desirable in case of cytoplasmic male sterility.
5) Transgressive segregation – Backcross method may be modified to produce Transgressive segregants.
6) Production of isogenic line.   

Genetic Consequences of Back Crossing:

1) It results in rapid increase in homozygosity and frequency of homozygote.
2) The repeated backcrossing results in increase in frequency of desirable genotype thus the genotype of progeny become increasingly similar to recurrent parent.
3) The gene under transfer must be maintained by selection in the back cross generation. Therefore, there would be opportunity in each backcross generation for crossing over to occur between the gene being transferred and tightly linked genes.

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