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The stem rust of wheat (Puccinia graminis f.sp. tritici) is one of the most important diseases of wheat in Iran and causes severe yield loss in some years when there is favourable condition for disease epidemic. In recent years, a new race of stem rust (Ug99) and its new variants have been emerged which are virulent on most resistance genes such as Sr31, Sr38, Sr36, etc., and have potential to spread rapidly and cause severe yield loss. The Ug99 race was first reported in 2009 from Lorestan and Hamadan provinces of Iran. Recent study which was conducted in 2011-2013 in Iran, showed that there was virulence on Sr36, Sr38, SrMcN and SrTmp genes and since these genes have been used widely in genotypes resistant to Ug 99, there is possibility of breakdown of these genes in Iran. Therefore, the genetic variability of the pathogen should be continuously investigated and based on these information, resistance sources should be developed. To achieve this goal, 56 stem rust differential cultivars/lines obtained from the Cereal Research Center, Manitoba, Canada were planted in Ardebil, Lorestan, East Azarbaijan, Hamadan, Khuzestan and Golestan provinces of Iran in natural field conditions. The seeds of each cultivar/line were planted in two 1 m length rows and irrigated every 10 days to promote the disease development. The disease severity and type of infection of each cultivar/line was recorded based on the standard protocol at late flowering stage. In the first year, the disease was developed only in Ardebil location, and there was no disease in other locations. In Ardebil, the SrMcN was the most susceptible gene, however, there was no virulence on Sr5, Sr21, Sr9e, Sr7b, Sr11, Sr6, Sr36, Sr9b, Sr30, Sr9a, Sr9d, Sr24, Sr31, Sr38, Sr8b, Sr9h, Sr12, Sr16, Sr19, Sr20, Sr22, Sr26, Sr27, Sr28, Sr32, Sr37, Sr39, Sr40, Sr41, Sr42, Sr43, Sr44, Sr45, Sr47, Sr50 and Sr53 genes. Other genes were moderately susceptible to susceptible. In the second year, the disease was developed in all locations except Golestan province. SrMcN, Sr9h and Sr42 were the most susceptible genes in all locations. However, there no virulence was observed on Sr24 and Sr47 genes (except Khuzestan). Other genes were moderately resistant to susceptible. The gene Sr31 was resistant in Ardebil and Khuzestan, moderately susceptible in Lorestanand, E. Azarbaijan and susceptible in Hamadan. The gene Sr36 was susceptible in Lorestan, moderately susceptible in Hamadan and Khuzestan and moderately resistant in E. Azarbaijan. Similarly, the gene Sr38 was susceptible in Ardebil, Lorestan and E. Azarbaijan, and resistant in Hamadan. It seems that Sr36 and Sr38 have no potential to be used in breeding for stem rust resistance in Iran. However, Sr24 and Sr47 genes which were resistant in locations (except Khuzestan) are recommended to be incorporated in breeding wheat for stem rust resistance. In addition, Sr31, Sr26, Sr27 and Sr28 genes which were relatively resistant in most locations have potential to be combined with Sr24 and Sr47 genes in wheat breeding programs. Key words: wheat, stem rust, trap nursery
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