Effective and ineffective resistance genes and reaction of promising wheat lines to stem rust in Ardabil

Stem (black) rust caused by Puccinia graminis f. sp. tritici is the most devastating of wheat diseases. Historically, it caused severe crop loss in many parts of the world. The cheapest and most environmentally friendly management strategy is the use of resistant wheat cultivars. Hence, the knowledge of effective resistance genes and determination of resistant sources will enable breeders to target those useful genes/resistant sources in their breeding programs. In order to determine effective resistance genes, virulence pattern of wheat stem rust was studied under the field conditions by planting of differential sets. Moreover, slow rusting parameters including final rust severity (FRS), apparent infection rate (r), relative area under disease progress curve (rAUDPC), and coefficient of infection (CI) were evaluated in a set of twenty-five wheat genotypes. The survey was conducted in Ardabil Agricultural Research Station, Northwest Iran, during two crop seasons 2013-2014 and 2015-2016. Results showed that there was no virulence for differential sets carrying resistance genes Sr5, Sr13, Sr22, Sr24, Sr26 + Sr9G, Sr27, Sr32, Sr35 and Sr36. But, virulence was observed for differential sets having resistance genes; Sr25, Sr7a, Sr23, Sr28, Sr29, Sr30, Sr33, Sr34, Sr37, SrDP2, SrGT, SrWLD, SrH. The genes found effective against stem rust under natural conditions may be deployed singly or in combinations with durable resistance genes to develop high yielding resistant wheat cultivars. Based on the results of evaluations for slow rusting parameters, seven lines together with susceptible check that had the highest values of FRS, CI, r and rAUDPC, were selected as susceptible lines. Six lines showed moderate or moderately susceptible reaction (M, MR, MS). Accordingly, these lines with low values of parameters are supposed to have gene (s) for varying degrees of slow rusting resistance. The remaining lines may have low level of slow rusting resistance that need further study to elucidate their nature of resistance.