The cultivated potato is a major crop worldwide. It is a high input crop with complex quality requirements at harvest and during storage. Potato breeders are fortunate to have access to a very diverse and accessible germplasm resource. Wild Solanum relatives provide genetic diversity as well as genes for valuable production and quality traits. In most cases, crossing success can be predicted based on endosperm balance number (EBN), or effective ploidy, of the parents. Crossing barriers between most wild species and the cultivated potato are the consequence of differences in EBN and can be easily overcome using ploidy manipulations and bridge crosses. The most common ploidy manipulations include haploid extraction to reduce EBN and 2n gamete production to increase EBN. Additional methods to produce fertile interspecific hybrids include mentor pollination, embryo rescue, hormone treatments, reciprocal crosses, selection of cross-compatible genotypes and somatic fusion. Knowledge of crossing barriers and mechanisms to overcome them allows potato breeders access to the rich gene pool in the genus Solanum.

Late blight 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 late blight resistance. We screened 384 accessions of 68 different wild potato species available from the U.S. Potato GeneBank against the late blight pathogen Phytophthora infestans in a detached leaf assay (DLA). Although all plants in 271 accessions were susceptible, all screened plants in 39 accessions were resistant. A mixture of resistant and susceptible plants were found in 34 accessions. All tested plants showed a partial resistance phenotype in 2 accessions, segregation of resistant and partial resistant plants in 9 accessions, segregation of partially resistant and susceptible plants in 4 accessions as well as segregation of resistant, partially resistant and susceptible individuals in 25 accessions. We found several species that were never before reported to be resistant to late blight. These new species could provide novel sources of late blight resistance. P. infestans clonal lineage-specific screening of selected species was conducted to identify the presence of RB resistance. We found late blight resistant accessions in S. verrucosum, S. stoloniferum and S. morelliforme that were susceptible to the RB overcoming isolate NL13316, indicating the presence of RB-like resistance in these species.

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