Principles of Plant Breeding (2+1)

Applications of back cross breeding

1. Inter varietal transferring of simply inherited traits. Characters governed by one or two genes like disease resistance are successful. 2. Inter varietal transfer of quantitative characters and highly heritable quantitative characters like earliness, plant height, seed size and seed shape is transferred.
2. Inter specific transfer of simply inherited characters: Disease resistance is transferred from related species to cultivated species. Inter specific transfer of genes are easy when the chromosome of the two species pair regularly.
3. Transferring of cytoplasm: wild species cytoplasmic are transferred to cultivated species transfer of male sterility. The variety or species from which the cytoplasm is to be transferred is used as the female parent. The parent to which the cytoplasm is to be transferred is used as the male parent in the original cross and back cross. After 6-8 back crosses the progeny would have the nuclear genotype of the recurrent parent and the cytoplasm from the donor parent.
4. Transgressive segregation: F1 is back crossed to one or two times to the recurrent parent leaving much heterozygosity for transgressive segregation to appear. In the second modification two or more recurrent parent may be used in the back cross progeny to accumulate genes from them into the back cross. Progeny of the new variety is not exactly like any one of the recurrent parent.
5. Production of isogenic lines : Isogenic lines are identical in their genotype except for one gene
6. Germplasm conversion: When valuable germplasm cannot be utilized in breeding programmesand may be used as recurrent parent in separate back cross programme these lines are called converted lines.

   Non recurrent aa	X	Recurrent parent AA
   F1	Aa X AA
   BC1		50% X AA
   BC2		75% X AA
   BC3		81% X AA
   BC4		93% X AA
   BC5		98.1% X AA
   BC6		98.4%

7. Recurrent parent: In back cross breeding the parent to which one or few genes from the donor parent are transferred.
8. Non recurrent parent: The donor parent from which the character is to be transferred.