Pyricularia grisea, the causal agent blast disease in rice, is considered as one of the most important fungus in paddy fields. Isolates of Pyricularia grisea were analyzed by SSR to determine the amount of genetic variability in populations. Fourteen primers were applied and DNA bands of 95-640 bp were produced. Cluster analysis using UPGMA method gave three groups. Group 1 was the major group and most of isolates which collected from west of Guilan belonged to this group. Groups 2 and 3 belonged to the center of Guilan isolates and the east of Guilan isolates, respectively. The results revealed although genetic distance was high between isolates of west and east of Guilan and the genetic similarity among these isolates of these two populations was low, but there was the maximum of genetic distance or the minimum of genetic similarity between the population of center of Guilan isolates and population of east of Guilan isolates. The minimum of genetic distance or the maximum of genetic similarity there was between the population of center of Guilan isolates and population of west of Guilan isolates. Overall, results confirmed that microsatellite primers are good and suitable markers for analyzing the population structure of Pyricularia grisea.

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