Retrospective View of North American Potato Breeding in the 20th and 21st Centuries

Cultivated potato (Solanum tuberosum Group Tuberosum), a vegetatively propagated autotetraploid, has been bred for distinctive market classes. Breeding efforts have relied almost entirely on phenotypic selection of populations developed by making intra- and inter-market class crosses and introgressions from wild and cultivated Solanum relatives. To retrospectively explore the history of potato breeding at the genome level, we genotyped a 250 clone panel with release dates ranging from 1857 to 2011 using the SolCAP 8300 Infinium SNP chip. Population structure analysis revealed four subpopulations within the panel, with the cultivated potato clones grouping together. Pair-wise kinship estimates revealed clear separation of the market classes and three distinct sub-groups of chip processing clones. The chip processing market class, for which wild species introgression has been used to introduce market quality traits, had the greatest average percent heterozygosity (59%) while the average in all cultivated potato clones was 56%. Through modern breeding efforts there has been minimal change in percent heterozygosity or the frequency of homozygous, single dose, and duplex loci, suggesting that sufficient heterozygosity had been achieved prior to formal breeding efforts in the mid-1800s. Phenotypic evaluation of the panel revealed not only diversification among market classes for traits under selection pressure but also improvement within market classes over the course of historical breeding efforts such as chip color within the chip processing clones. While diversification and improvement have occurred through phenotypic selection, understanding the genetic basis of traits will allow for more rapid improvement in potato breeding.