Rhizoctonia is one of the inhabitant Basidiomycets which is distributed unevenly in most soil and its isolation is difficult from soil. Rhizoctonia solani with AG-3 and AG-4 anastomosis groups are the most importat pathogene on plants in Isfahan region. During 2015-2016 potato, bean and onion samples were collected. Three hundred and two isolates of Rhizoctonia recognized as which based on nuclear numbers and hyphal dimentions 227 isolates were multinucleate and 25 isolates were binucleate. Anastomosis group of multinucleate were determined using 12 AG isolates. Of which AG-3, AG-4, AG-5, AG-2-1, AG-2-2, AG-13 on potato, AG-1-1, AG-2-1, AG-2-2-, AG-6, AG-4 on bean, AG-4 on onion were identified. Morphological features including form and color of colony, form, color and sclerotial formation in culture, and optimum temperature for growth were determined. Patogenecity test was performed using potato, bean and onion plants under green house condition. Based on the results obtained in this study, AG-4 and AG-2 have wide range of host than other anastomosis groups. However increasing the percentage of dead plants by AG-4 and AG-2 compared to other anastomosi groups which were identified in the three hosts, were also observed. All of the anastomosi groups which inoculated potato plant were virulent except AG-6 and AG-1 on bean plant. The highest percentage of potato plants which were inoculated by AG-3 and AG-4 were dead. All of the anastomosis groups which inoculated on bean plant except AG-5, AG-3 and AG-13 were pathogenic on potatoes. Most of dead plants were happened through inoculation of bean by AG-4. Only AG-4 which identified among three hosts was pathogen on onion. Through inoculation, symptoms of other AG didn’t observe on onion. This is the first report of AG-4 on onion and AG-13 on potato in Iran. In order to confirm morphological studies, after DNA extraction, ITS1/ITS2 and ITS1/ITS4 primer pairs we used. Amplified DNA was sequenced. The results of the Blast revealed the 99 and 100% similarity of isolates of Rhizoctonia to available sequences in Gen Bank. Due to the wide distribution of AG-4 on each hosts including potatoes, beans and onions and formation of sclerotia in the soil.The results of this study showed that crop rotation with these hosts need to be done carefully. Keywords : Isolation, culture media, Rhizoctonia solani , anastomosis group
