Multiple-site identification of potato parent clones conferring high levels of late blight resistance with a corresponding genetic model for resistance

Abstract

Toluca Valley, Mexico, is the putative center of origin and diversity forPhytophthora infestans (Mont.) de Bary, the oomycete pathogen responsible for late blight, making it an ideal location for screening potato breeding populations for late blight resistance. Approximately 21,500 progeny from the USDA-ARS, Aberdeen, Idaho potato breeding program were evaluated from 1996 through 2005 by estimating the percentage of defoliation due to late blight throughout the growing season. Comparisons of the number of resistant progeny and their degree of resistance response from resistant x susceptible (RxS) and resistant x resistant (RxR) crosses were made across years. A clone of each progeny planted in Toluca Valley was also planted the same year near Aberdeen, Idaho, to screen for acceptable tuber type. Promising progeny phenotypes were then screened the following year for tuber late blight resistance at field plots near Corvallis, Oregon. The RxR late blight crosses produced 64% resistant progeny compared to 29% of the RxS crosses. The segregation for late blight resistance in progeny from specific RxS crosses best fits a 1R:3S ratio. This segregation ratio is best explained by a gene model in which resistance is conferred by the presence of a dominant allele at each of two loci. The greater percentage of resistant progeny from RxR crosses indicates the benefits of pyramiding resistance genes from diverse germplasm. Three promising late blight resistant parental clones with acceptable tuber type resulted from family A95053. Family A95053 has multiple sources of resistance that includeSolarium demissum andSolarium stoloniferum, via female parent AWN86514-2 and male parent, B0718-3.