characterizing different taxonomic groups of rhizoctonia spp. fungi associated with root and crown rot on sugar beet by analyses of rdna-its and pcr-rflp

abstract isolates of rhizoctonia spp., obtained from sugar beet roots and crowns with dry rot symptoms that had been collected from various sugar beet production regions in khorasan razavi province during 2008 and 2009, were investigated in this research. characterization by conventional techniques and molecular methods using species-specific primers was carried out. results showed that from 36 isolates, 31 were r. solani and 5 were r. cerealis. in restriction fragment length polymorphism analysis of pcr-amplified ribosomal dna internal transcribed spacer region of r. solani taxonomic group, isolates of subgroup ic of ag1 were recognized. of 31 isolates identified as r. solani, 17 were ag2-2 iiib, 12 were ag2-2 iv, and 2 were ag1-ic. pathogenicity tests on sugar beet cultivar fd0432 revealed that isolates of ag2-2 iiib and ag2-2 iv were more virulent on root and crown of sugar beet plants compared to ag1-ic and r. cerealis. whereas, isolates of r. cerealis had the most virulence on seedlings. this is the first report of characterization and investigating pathogenicity of various subgroups of r. solani ag1 and ag2-2, and also binucleate r. cerealis isolated from sugar beet in iran.