Utilization of potato genetic resources in variety development

Potato varieties of Europe, widely grown prior to the late blight epidemic of the 1840s, were apparently derived mainly from Chilean Solanum tuberosum Group (Gp) Tuberosum and with contributions from Gp Andigena. A small number of these old varieties had field resistance and consequently survived the late blight. These survivors, along with a limited number of 19(th) and early 20(th) century introductions, provided the very narrow genetic base for our modern potato variety development. Beginning in the first half of the 20(th) century, resistance to diseases and pests from exotic species and primitive relatives was backcrossed into the existing parental stocks, with little improvement in broadening of the genebase. By the 1980s, 77% of European and somewhat fewer North American varieties had genes, derived by backcrossing, from S. demissum (late blight resistance) and Andigena (resistance to cyst nematode). Broadening of the Tuberosum genebase was undertaken in 1959 by creating long-day adapted Neo-Tuberosum (N-T) from large populations of Andigena. This took six or more cycles of recurrent mass selection. Simmonds, in England, was the first to begin this work, followed shortly after by Plaisted, in the U.S., and Tarn, in Canada. Varieties with N-T in their pedigrees include the New York releases "Rosa", which is 50% N-T, and "Eva", 25% N-T. The Tuberosum genebase has also been broadened with diploid Gp Phureja resulting in the releases of "Yukon Gold," with yellow flesh and high internal quality, and "NorValley," a chipper with resistance to cold sweetening. Over 5000 accessions of about 150 wild species are available to breeders from the U.S. Department of Agriculture, National Research Support Project 6 (NRSP-6) genebank. Many of these accessions have been evaluated for resistance to diseases and pests as well as other important traits. Six genebanks in other countries also have many accessions for breeders. These seven collections are a great source of valuable traits for breeding, but remain under-utilized, mainly because of the time and additional resources required in eliminating the "wildness" characters associated with the desired traits. "Pre-breeding" is needed to help breeders utilize the many needed genes and alleles in the wild species. There now are two projects with pre-breeding as an objective in the U.S., one at Madison, WI, and the other at Prosser, WA. Resistance to cold sweetening (low sugar build up in cold storage) has been backcrossed from several wild species into the Tuberosum background, as has resistance to late blight, the Columbia rootknot nematode, and the potato leafroll virus (PLRV). Resistance to potato virus Y (PVY) and PLRV obtained from N-T has been incorporated into Tuberosum parental stocks. Durable resistance to late blight in Polish breeding stocks, with S. demissum and S. stoloniferum background, and in improved Bolivian and Peruvian Andigena has also been utilized by North American programs.