Chapter 13 - The Pedigree Method

Abstract

The pedigree breeding method is the most widely used scheme for improving populations of self-pollinated plant species. The method begins with the hybridization of two homozygous parents that are selected for mutual phenotypic complementation. A small number of F1 plants are grown to produce a large population of F2 individuals. At this juncture, a program of recurrent selection and self-matings proceeds until the drive to allele fixation reaches a prescribed end point, usually the F7 or F8 generation. During the early generations (F2 to F4), selection intensity is low and conducted both within and among families due to VD effects. In later generations (F5 to F7 or F8), VD is a minimal factor, so selection intensity is stronger and practiced among families. As the number of parental polymorphisms increases, the theoretical necessary population sizes to recover all potential recombinants increases exponentially. Linkage, low heritability, and unintended cross-pollination can reduce the effectiveness of the method. The number of repulsion linkages and map distance between loci also proportionally increases the theoretical population size to recover targeted recombinant coupling linkages. The pedigree breeding method has been significantly improved by the availability of computer software programs that have reduced labor needs for field organization and data collection and analyses. The parents are chosen based on assortative properties for general “background” phenotypes and disassortative properties for phenotypes destined for transfer, complementation, or improvement. MAS for QTL is a tool of immense potential benefit in the pedigree method for improving the accuracy of selection for phenotype and fixation, improving the effectiveness and efficiency of the program. It is possible and under certain circumstances advisable to mix breeding strategies in a program; for example start with the pedigree strategy then switch to an alternative (see Chapter 14).