A total of one hundred and seventeen isolates of Magnaporthe grisea , the causal fungus of rice blast, including fifty three isolates from different regions of Guilan province and sixty four isolates collected from experimental field of Rice Research Institute of Iran (RRII) in Rasht have been studied for evaluation of genetic diversity of fungus based on determination of vegetative compatibility groups (VCGs). VCGs among these populations were studied through isolating nitrate non-utilizing mutants in each isolate. The results reveald that M. grisea population can be divided into three VCGs, designated as VCG1, VCG2 and VCG3. VCG2 was the most common group in these areas, while VCG1 and VCG3 were the second and third most prevalent VCGs. Among isolates from different regions of Guilan, 42.30%, 55.76% and 1.92% of isolates belonged to VCG1, VCG2 and VCG3, respectively. Also, 34.37%, 60.93% and 4.68% of isolates from experimental field of RRII belonged to VCG1, VCG2 and VCG3, respectively. Totally, 37.93%, 58.62% and 3.44% of the total isolates of the two populations were grouped into VCG1, VCG2 and VCG3, respectively. Isolates of VCG1 and VCG2 were collected from cultivars Binam, Taroom-Molai and Hashemi. Most of the isolates from cultivars Khazar and Hasani belonged to VCG2. This investigation revealed the fact that the fungus population shows low genetic diversity. Moreover, characterization of vegetative compatibility groups is a useful method for evaluation of genetic diversity in M. grisea populations.
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