Pathotypes of Blumeria graminis f.sp. tritici, the Causal Agent of Wheat Powdery Mildew from some Regions of Iran

Wheat powdery mildew is an important disease of wheat especially in humid areas. The disease which is caused by Blumeria graminis f.sp. tritici , has recently become serious in different provinces of Iran.The present study was carried out to investigate virulence factors and pathotypes of the pathogen in different provinces of Iran. Infected samples of wheat were collected from different provinces in 2005 and transferred to the greenhouse at Seed and Plant Improvement Institute in Karaj. After purification and multiplication of spores on susceptible cultivar Bolani, 18 isolates were evaluated for their virulence genes. Pure spores of each isolate was inoculated separately on the first leaves of 17 near isogenic lines (differentials) in the greenhouse. Infection types were assessed based on 0 to 9 scale, 12 and 16 days after inoculation. From the total of 18 isolates of Blumeria graminis f.sp. tritici , 14 pathotypes were identified. This indicated the high genetic variability in the population of the pathogen and presence of different pathotypes. Pathotypes No. 6 and 12 from Varamin with 87.8 % pathogenicity , were the most virulent pathotypes. Only one of the pathotypes were isolated from more than one region. High frequencies of virulence for genes Pm3b , Pm5 and Pm3d were found. Frequencies of virulence for Pm1,2,9 and Pm 2,4b,8 were low. Comparing the results of virulence surveys in different provinces during 2000 to 2006 showed an increase in frequencies of virulence for some resistance genes while virulence for some of genes had been decreased. It shows frequently variable pathotypes in every region.