Pathogenicity Variation in Isolates of Mycosphaerella graminicola the Septoria tritici Blotch Pathogen on Differential Cultivars

In the present study seedling response of 21 wheat differential cultrivars carrying different Stb resistance genes and four check cultivars to thirteen isolates of M. graminicola، collected from Golestan، Khuzestan and Ilam provinces during 2011، 2012 and 2013، were investigated in greenhouse، using a completely randomized design. Analysis of variance on leaf necrosis area and pynidial coverage percentage showed significant differences at 1% probability level among the isolates and also isolate × cultivar، indicating high variation in pathogenicity of isolates and specific interaction between isolates and cultivars. Cluster analysis of the data showed that Riband (Stb15) and Shafir (Stb6) cultivars were the highly resistant and highly susceptible cultivars to all isolates، respectively. Isolates showed different virulence patterns on differential cultivars. Isolate SPII91005 from Gorgan with 42% necrosis area and 41% pycnidial coverage had the highest and isolate SPII91004 from Sardasht with 19% necrosis and pycnidial coverage had the lowest disease severities. The results of this investigation showed a high variation in pathogenicity of the isolates which can be related to the virulence factors exist in these isolates.