Phenotypic and molecular characterization of resistance to stem rust in wheat cultivars and advanced breeding lines from Iran and Syria

Seedling and adult-plant response to stem rust of 103 Iranian and Syrian bread and durum wheat genotypes was investigated using stem rust races TKTTC and TTKSK in seedling tests and TKTTC and TTKST at the adult-plant stage. The same genotypes were characterized with simple sequence repeat (SSR), sequence tagged site (STS) and cleaved amplified polymorphic sequence (CAPS) markers linked to Sr2, Sr22, Sr24, Sr25, Sr26, Sr31, Sr36, Sr39, and Sr46. In seedling tests, three phenotypic groups were identified: those lacking effective resistance genes, those postulated to carry Sr31, and those that were resistant to TKTTC and TTKSK. Adult-plant assessment indicated the presence of adult-plant resistance (APR) to TKTTC and TTKST mainly due to Sr2 and uncharacterized resistance gene(s). Using molecular markers, Sr2 was confirmed as the most common resistance gene detected in Iranian genotypes. It was detected alone in 38 genotypes, in combination with Sr31 in 11 genotypes, and combined with Sr31+Sr25 in one genotype. In total, Sr31 was postulated in 19 genotypes. Among Syrian genotypes, Sr2 was detected alone in one and in combination with Sr31 in two bread wheat cultivars. No diagnostic DNA fragment associated with the markers was present in the durum wheat genotypes. Haplotype analysis of 103 genotypes using Sr2-linked markers csSr2 and STS#Sr2 indicated that csSr2 was a better predictor of the presence of Sr2 gene in wheat.