Evaluation of wild Solanum species for resistance to the US-8 genotype of Phytophthora infestans utilizing a fine-screening technique

Greenhouse assays were carried out to characterize Solanum accessions previously reported to be late blight resistant and to identify individuals within the accessions with high levels of resistance to late blight. Foliage of wild Solanum species accessions or hybrid cultivated potato x wild species (diploid or tetraploid) from Mexico, Russia, or South America was inoculated with Phytophthora infestans (US-8) and was scored for severity of foliar symptoms at 7 and 14 days after inoculation (DAI). Mexican accessions (S. brachycarpum, S. pinnatisectum, S. guerreroense, and S. fendleri) were significantly more resistant (1.1% infection at 14 DAI) than either Russian (59.1% infection at 14 DAI) or South American (53.4% infection at 14 DAI) accessions. Moreover, the genotypes within the Mexican accessions tended to be more uniformly resistant whereas genotypes within the Russian and South American accessions tended to segregate for resistance. The more resistant genotypes of Russian and South American accessions (176/546) were retested, and 56 genotypes were identified as having potential for use in potato breeding programs for resistance to late blight. Fifty percent of the selected genotypes were from S. microdontum accessions PI498124, PI595510, and PI595511. The potential of these species for incorporation into breeding programs for late blight resistance is discussed.