Characterization and mapping of Rpi1, a late-blight resistance locus from diploid (1EBN) Mexican Solanum pinnatisectum

Solanum is a diverse genus with over 200 species occupying a range of habit ats from the Southwestern United States to Central Chile. Germplasm evaluat ions have focused on species that can be crossed with S. tuberosum, while M exican diploid (2n = 2x = 24) Solanum species with an Endosperm Balance Num ber (EBN) of 1 have received less attention because of poor crossability du e to their ploidy and EBN. Recent changes in Phytophthora infestans populat ions have increased the need for new sources of genetic resistance to this fungus. We have characterized resistance to P. infestans in the Mexican 2x (1EBN) species S. pinnatisectum. An interspecific hybrid between resistant S. pinnatisectum and susceptible S. cardiophyllum plants was backcrossed to S. cardiophyllum to generate a family segregating for late-blight resistan ce. The diploid (1EBN) genetic map generated with 99 RFLP markers revealed extensive synteny with previously published potato maps. A single dominant late-blight resistance locus (Rpi1) from S. pinnatisectum was mapped to chr omosome 7, a region previously not associated with late-blight resistance. Characterization of the P. infestans isolate used for disease evaluations r evealed that it possessed the avirulence gene corresponding to the R9 resis tance locus, indicating that Rpi1 could possibly correspond to R9.