Multiple R genes referring to resistance against Phytophthora infestants were identified in different potato species, and the majority of these R genes were applied in potato breeding programs. The aim of the study was to use gene-based markers to discriminate between resistant and susceptible potato genotypes to late blight (LB). Furthermore, we correlated phenotype data obtained from the detached leaf assay with genotypic results to confirm the polymerase chain reaction (PCR)-based screening results. A total of 17 potato genotypes were tested for resistance to P. infestans, using the detached leaf assay. These genotypes gave different responses to resistance against LB, ranging from highly resistant to moderately susceptible. Our results showed that the data from the laboratory evaluation were run in parallel with the greenhouse experiment. Besides, these genotypes were assayed by the sequence-characterized amplified region and cleaved amplified polymorphic sequence markers for R genes. The results of PCR products could be used to distinguish between potato genotypes resistant and susceptible to LB. On the other hand, there is no correlation between the levels of resistance to LB and the number of R gene markers. The highest number of resistance gene markers was scored in the moderately resistant wild species Solanum stoloniferum CGN 17605 (8), followed by the highly resistant potato variety Jelly (7). In contrast, the lowest number of markers was found in the moderately resistant potato variety Deta (3). Results of the study showed that the presence of more than allele of the same gene in a single genotype give a durable resistance against different races of P. infestans. Therefore, potato genotypes that have multiple R genes could be taken into consideration in potato breeding programs for resistance against LB disease.
Key words: Gene resources, Disease resistance, DNA markers, R genes, Solanum tuberosum L.
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