A resistance gene against potato late blight originating from Solanum × michoacanum maps to potato chromosome VII.

Solanum ×  michoacanum (Bitter.) Rydb. is a diploid, 1 EBN (Endosperm Balance Number) nothospecies, a relative of potato originating from the area of Morelia in Michoacán State of Mexico that is believed to be a natural hybrid of S. bulbocastanum × S. pinnatisectum. Both parental species and S. michoacanum have been described as sources of resistance to Phytophthora infestans (Mont.) de Bary. The gene for resistance to potato late blight, Rpi-mch1, originating from S. michoacanum was mapped to the chromosome VII of the potato genome. It confers high level of resistance since the plants possessing it showed only small necrotic lesions or no symptoms of the P. infestans infection and we could ascribe over 80% of variance observed in the late blight resistance test of the mapping population to the effect of the closest marker. Its localization on chromosome VII may correspond to the localization of the Rpi1 gene from S. pinnatisectum. When mapping Rpi-mch1, one of the first genetic maps made of 798 Diversity Array Technology (DArT) markers of a plant species from the Solanum genus and the first map of S. michoacanum, a 1EBN potato species was constructed. Particular chromosomes were identified using 48 sequence-specific PCR markers, originating mostly from the Tomato-EXPEN 2000 linkage map (SGN), but also from other sources. Recently, the first DArT linkage map of 2 EBN species Solanum phureja has been published and it shares 197 DArT markers with map obtained in this study, 88% of which are in the concordant positions.