Identification of late blight, Colorado potato beetle, and blackleg resistance in three Mexican and two south American wild 2x (1EBN) Solanum species

Wild potatoes are important sources of genes for resistance to disease and insect pests. A collection of wild Mexican and South American Solanum species from the US potato Genebank was evaluated under laboratory and/or field conditions for their reaction to late blight (Phytophthora infestans), Colorado potato beetle (CPB, Leptinotarsa decemlineata Say), and blackleg (Erwinia carotovora subsp. atroseptica (van Hall) Dye) in order to identify individual genotypes with multiple resistance genes. Late blight inoculations using aggressive isolates (US-8/A2 and US-11/A1 mating types) of P. infestans revealed a wide range of variation for resistance between and within the accessions of the wild species tested. For late blight, susceptible as well as moderately to highly resistant genotypes were observed in all the species tested. However, at least one accession from the three Mexican and one South American wild diploid species tested showed a relatively uniform high level of resistance to P. infestans. These included S. bulbocastanum, S. pinnatisectum, S. cardiophyllum, and S. circaeifolium. Two accessions from South American species S. commersonii were highly susceptible to late blight. For the Colorado potato beetle test, only one species, S. pinnatisectum appeared uniformly resistant to CPB under field conditions. Results of screening for blackleg resistance showed that there were major differences between genotypes in the wild species. Accessions of S. circaefolium PI 498119 and S. bulbocastanum PI 243504 were identified as having significantly higher blackleg resistance than cultivated potato and the other wild species tested. However, genotypes from these two accessions were more susceptible to late blight and CPB. Characterization of the P. infestans isolate P1801C.16 used for late blight evaluation and multi-locus isolate tests using US-8/A2 and US-11/A1 races revealed that the resistance in S. pinnatisectum genotypes tested corresponded to a race-non-specific genetic system, which was different from any existing R genes. Solanum pinnatisectum genotypes with both high levels of late blight and CPB resistance as well as blackleg resistance genotypes identified in the present study represent a diverse gene pool that may be useful for development of new potato cultivars with multiple disease and insect resistance. The potential utilization of these valuable sources for improvement of cultivated potato is discussed.