The late blight resistance locus Rpi-blb3 from Solanum bulbocastanum belongs to a major late blight R gene cluster on chromosome 4 of potato

Late blight, caused by Phytophthora infestans, is one of the most devastating diseases in cultivated potato. Breeding of new potato cultivars with high levels of resistance to P infestans is considered the most durable strategy for future potato cultivation. In this study, we report the identiflcation of a new late-blight resistance (R) locus from the wild potato species Solanum bulbocastanum. Using several different approaches, a high-resolution genetic map of the new locus was generated, delimiting Rpi-blb3 to a 0.93 cM interval on chromosome 4. One amplification fragment length polymorphism marker was identified that cosegregated in 1,396 progeny plants of an intraspecific mapping population with Rpi-blb3. For comparative genomics purposes, markers linked to Rpi-blb3 were tested in mapping populations used to map the three other late-blight R loci Rpi-abpt, R2, and R2-like also to chromosome 4. Marker order and allelic conservation suggest that Rpi-blb3, Rpi-abpt, R2, and R2-like reside in the same R gene cluster on chromosome 4 and likely belong to the same gene family. Our findings provide novel insights in the evolution of R gene clusters conferring late-blight resistance in Solanum spp.