Vertical resistance to late blight in wild potato species from Argentina

The possible presence of vertical resistance to late blight conferred by R genes in Argentine wild Solanum species, which presumably have not evolved under the pressure of the fungus, was investigated. Solanum microdontum, S. commersonii and S. chacoense clones were tested in the greenhouse and with detached leaves in the laboratory after inoculation with a complex race an d a non-virulent race of Phytophthora infestans. Two progeny tests were car ried out to assess the performance of contrasting parents in regards to the ir resistance. A varying frequency of incompatible clones was detected amon g the species, with S. microdontum having the higher proportion of clones y ielding incompatible reactions both in the laboratory and in the greenhouse . S. chacoense and S. commersonii showed a small but still considerable fre quency of incompatible clones. The progeny tests confirmed the presence of R genes in a S. commersonii cross and their absence in a S. chacoense cross . The unexpected presence of R genes, its evolutionary significance and the consequences on the use of these species in breeding is discussed.