Research Objective 3

Objective 3 builds on Objective 2 to create germplasm appropriate for use in cultivar development. We will use populations of genetically distinct plants generated in Objective 2b to initiate a recurrent selection program. The goal will be to develop partially inbred lines fixed for major market traits.

Roles of Objectives 2 and 3 in the transition from tetraploid to diploid germplasm for breeding.

One of the major challenges with conventional potato breeding is the undesirable and unpredictable variation in offspring created by crossing tetraploid clones that have multiple alleles for each gene. We will address this problem by moving germplasm toward homozygosity where each gene has only a single allele. This is a new direction in potato breeding and it is not a trivial endeavor. However, the development of inbred lines is necessary as the foundation for the creation of diploid hybrid varieties. Phenotypic selection alone will identify clones with lower than expected levels of homozygosity for a given stage of inbreeding because of the negative relationship between vigor and homozygosity (i.e., inbreeding depression). To avoid this bias, during recurrent selection, plants will be genotyped with genome-wide markers, and percent homozygosity will be considered together with the phenotypic traits.

Generalized recurrent selection scheme. Solid lines show the expected loss of vigor and self-fertility during inbreeding. Dashed lines illustrate the restoration of traits after intermating. As cycle number increases, plants become more inbred (i. e. they have higher homozygosity) and for each level of homozygosity they become more vigorous.