Rhizoctonia solani RBL1, isolated from naturally infected rice plants with typical symptoms of sheath blight in a paddy field of Mazandaran province, Iran, was used in all experiments. R. solani strain RBL1 was obtained from the culture collection of the Iranian Rice Research Institute. The fungus was purified with the hyphal tip method and maintained on potato dextrose agar (PDA, Merck, Germany). To prove pathogenicity, inoculations were done in a glasshouse on Oryza sativa cv. Neda by placing a 5-mm mycelial plug of R. solani between the junction of the basal leaf sheath and the stem above the water line at the maximum tillering stage. R. solani was re-isolated from characteristic lesions of sheath blight. To confirm the anastomosis group (AG) and subgroup, a nuclear rDNA region, containing the ITS1 and 2 as well as the 5.8S gene (accession No. HM211085) was subjected to a BLAST search (Altschul et al., 1997) to find out the most similar sequences in the NCBI GenBank