Stem rust of wheat, caused by Puccinia graminis f.sp. tritici, has been historically one of the most important diseases of wheat in Iran. The disease has been reconsidered in Iran due to its re-emergence and the observation of the dangerous Ug99 race in some parts of the country. The present investigation was conducted to detect stem rust effective resistance genes by developing stem rust trap nurseries consisting of 49 lines of wheat each carrying a single resistance gene of stem rust (Sr) and seven lines each carrying Sr multigenes under natural disease infection in four locations for two cropping seasons of 2016-2017 and 2017-2018. All commercial wheat cultivars and candidate lines from Iran were also included to the nurseries to determine their reaction to stem rust. Disease was scored by recording disease severity and infection type at adult plant stage when disease well developed on flag leaves of susceptible checks. Results showed presence of virulence for several Sr genes in one or more locations/years. In contrast, the single genes of Sr24, Sr26, Sr36, Sr38, Sr39,

Sr40, and the complex genes of Sr24i-Sr31, Sr24i-Sr1RS-Am, Sr7ai-Sr6i-Sr12 and Sr6i-Sr24i-Sr36i-Sr1RS-Am were still effective against stem rust in all locations. However, virulence for Sr36 and Sr38 have already been reported from the locations investigated in the present study. The results of determination of reaction of commercial wheat cultivars and candidate lines showed that the wheat cultivars Atrak, Baharan, Karkheh, Arya, and Dena and the candidate lines of N93-5, N-93-17, N-94-8, N-96-22, N-96-23, S-92-11, CD-89-10, CD-90-4, M-92-18, MS-93-14, and DM-92-17 still have resistance to stem rust in all locations investigated for one or two years.