The bulk-population

The bulk-population
  • At maturity the crop is harvested in mass, and the seeds are used to establish the next generation in a similar plot. No record of ancestry is kept.
  • During the period of bulk propagation, natural selection tends to eliminate plants having poor survival value.
The bulk-population method of breeding differs from the pedigree method primarily in the handling of generations following hybridization. The F2 generation is sown at normal commercial planting rates in a large plot.
Two types of artificial selection also are often applied
  1. Destruction of plants that carry undesirable major genes and
  2. Mass techniques such as harvesting when only part of the seeds are mature to select for early maturing plants or the use of screens to select for increased seed size. Single plant selections are then made and evaluated in the same way as in the pedigree method of breeding.
  • The chief advantage of the bulk population method is that it allows the breeder to handle very large numbers of individuals inexpensively.
  • Often an outstanding variety can be improved by transferring to it some specific desirable character that it lacks.
  • This can be accomplished by first crossing a plant of the superior variety to a plant of the donor variety, which carries the trait in question, and then mating the progeny back to a plant having the genotype of the superior parent. This process is called backcrossing.
  • After five or six backcrosses the progeny will be hybrid for the character being transferred but like the superior parent for all other genes. Selfing the last backcross generation, coupled with selection, will give some progeny pure breeding for the genes being transferred.
  • The advantages of the backcross method are its rapidity, the small number of plants required, and the predictability of the outcome.
  • A serious disadvantage is that the procedure diminishes the occurrence of chance combinations of genes, which sometimes leads to striking improvements in performance.

Last modified: Thursday, 1 March 2012, 7:28 PM