I. ALEKSEEV1, 3, M.A. KUZNETSOVA2, E.E. KHAVKIN1 1All-Russian Research Institute of Agricultural Biotechnology, Federal Agency of Scientific Organizations, 42, ul. <...> Timiryazevskaya, Moscow, 127550 Russia, e-mail katesokol83@mail.ru, seq@syntol.ru, jalex@iab.ac.ru, emil.khavkin@gmail.com; 2All-Russian Research Institute of Phytopathology, Federal Agency of Scientific Organizations, 5, ul. <...> Timiryazevskaya, Moscow, 127550 Russia Acknowledgements: The authors are grateful to the Center for Collective Use of Equipment «Biotechnology» (All-Russian Research Institute of Agricultural Biotechnology) for sequencing Avr clones and separating SSR amplicons by capillary electrophoresis. <...> The phytopathological evaluation of Phytophthora infestans isolates was performed as part of the State Commission 0598-2015-0018. <...> Received March 21, 2016 A b s t r a c t Potato late blight caused by oomycete Phytophthora infestans (Mont.) de Bary is economically significant disease of worldwide importance. <...> The traditional classification of specialized races of P. infestans is based on eleven resistance genes (R genes) introgressed from Solanum demissum to cultivated potato S. tuberosum. <...> The selection of potato varieties, each comprising one of these R genes, is referred to as the Mastenbroek-Black set of differential plants. <...> This set has been employed to establish the virulence genes (r genes) in isolates and strains of P. infestans, and collections of such individual strains have been maintained as tool sets of differential races for discerning R genes in cultivated and wild Solanum plants. <...> While widely used in potato breeding for late blight resistance, these differential races have not been sufficiently explored by present-day molecular methods. <...> When the differential races of P. infestans were genotyped with the standard set of 12 microsatellite (simple sequence repeat, SSR) loci, these races were distinct from reference A1 strains and highly aggressive lines lately dominant in the Western and Central Europe. <...> SSR clusters of differential races did not match their r gene profiles. <...> To assess the profiles of virulence genes in the differential races of P. infestans, we cloned three avirulence genes (Avr genes): ipiO = Avr-blb1, which recognizes the Rpi-blb1 = Rpi-sto1 gene of S. bulbocastanum and S. stoloniferum characterized by broad <...>