New races of Phytophthora infestans rapidly defeat potato late blight (LB) resistance based on Solanum demissum germplasm, and breeders search for new sources of durable LB resistance. We developed and verified six sequence characterized amplified region markers recognizing the race-specific genes R1 and R3 of S. demissum and the broad-spectrum resistance gene RB of S. bulbocastanum and the germplasms of these species and used them to screen 209 accessions of 21 wild Solanum species. In addition to S. demissum, homologues of R1 and R3 were found in several species of series Demissa,Longipedicellata and diploid Tuberosa; R3 homologues were also detected in S. bulbocastanum,S. cardiophyllum and S. ehrenbergii. The RB homologues were found in a wider range of Solanum species. The markers of R1 and R3 genes reliably discerned between germplasms of S. tuberosum ssp. tuberosum and wild sources of LB resistance. Following introgression, the species-specific markers of demissum and bulbocastanum germplasm were rapidly lost, whereas the markers of R1 and R3 genes lasted through several meiotic generations and were maintained at high frequencies in modern potato cultivars. The presence of these markers in demissoid potato cultivars was significantly associated with LB resistance, presuming that both genes contribute to overall defence response.

A coiled coil-nucleotide binding site-leucine-rich repeat gene RB/Rpi-blb1 isolated from Solanum bulbocastanum confers broad-spectrum resistance to Phytophthora infestans and is currently employed in potato breeding for durable late blight (LB) resistance. RB homologues were reported in several Solanum species; some of them retained defence function. Here, we report additional evidence on RB-like sequences in 21 Solanum species of the section Petota. The panel of Solanum species was screened with three RB-related PCR markers. RB-like sequences were found in every tested Solanum accession, suggesting universal distribution of RB structural homologues among Solanum genomes, while locus-specific RB-629 was found only in 15 species. Phylogenetic analysis of RB-629 sequences suggested a highly conservative pattern of polymorphisms that was neither species- nor series-specific. Apparently, duplication and evolution of RB-like loci preceded Solanum speciation. Marker presence and particular haplotypes were not immediately associated with high LB resistance.