Screening of Wild Potatoes Identifies New Sources of Late Blight Resistance.

Late blight (LB) of potato is considered one of the most devastating plant diseases in the world. Most cultivated potatoes are susceptible to this disease. However, wild relatives of potatoes are an excellent source of LB resistance. We screened 384 accessions of 72 different wild potato species available from the U.S. Potato GeneBank against the LB pathogen Phytophthora infestans in a detached leaf assay (DLA). P. infestans isolates US-23 and NL13316 were used in the DLA to screen the accessions. Although all plants in 273 accessions were susceptible, all screened plants in 39 accessions were resistant. Resistant and susceptible plants were found in 33 accessions. All tested plants showed a partial resistance phenotype in two accessions, segregation of resistant and partial resistant plants in nine accessions, segregation of partially resistant and susceptible plants in four accessions, and segregation of resistant, partially resistant, and susceptible individuals in 24 accessions. We found several species that were never before reported to be resistant to LB: Solanum albornozii, S. agrimoniifolium, S. chomatophilum, S. ehrenbergii, S. hypacrarthrum, S. iopetalum, S. palustre, S. piurae, S. morelliforme, S. neocardenasii, S. trifidum, and S. stipuloideum. These new species could provide novel sources of LB resistance. P. infestans clonal lineage-specific screening of selected species was conducted to identify the presence of RB resistance. We found LB resistant accessions in Solanum verrucosum, Solanum stoloniferum, and S. morelliforme that were susceptible to the RB overcoming isolate NL13316, indicating the presence of RB-like resistance in these species.