Principles of Plant Breeding (2+1)

Application of bulk method

1. Isolation of homozygous lines
It is used for the isolation of homozygous lines with a minimum of effort and expense. The population is carried to F6-F7 as Bulk, where it reaches homozygosity.Individual plants are selected and evaluated to derive pure line. So preliminary yield trails are conducted to derive homozygous lines.

2. Waiting for the opportunity for selection:
Selection for resistance to disease, lodging and cold depends upon the presenceof suitable environmental conditions favoring epidemic.Waiting till such environment do occur so the segregating generations are carried as bulk in such environment. Individual plants are selected and handled as in pedigree method.The duration of bulking depend upon the occurrence of the concerned environment. This is known as mass pedigree method of Harlan.

3. Opportunity for natural selection:
Maintainance of bulk is inexpensive and without much efforts. Some bulk populations are carried up to F20 to F30 to provide an opportunity for natural selection to act on their composition. Up to F6 the population is heterozygous and after F7 natural selection to act on homozygous plants and would change the frequency of homozygous genotypes present in the population. It is assumed that natural selection would favour higher yielding genotypes and eliminate poorer genotypes.