role of potato seed tubers in distribution of rhizoctonia solani ag-3

rhizoctonia disease of potato is one of the main causes of yield loss in this crop world- wide. in order to survey the importance of causal agent spread by seed tubers, 36 isolates of rhizoctonia solani were obtained from stored seed tubers and infected subterranean potato plant in the main potato production areas of hamedan and kurdistan provinces in the west of iran. the examination of anastomosis groups and nuclear conditions showed that all isolates were multinucleate and belonged to ag-3. in pathogenicity tests of 23 selected isolates, over 95 percent were able to cause rhizoctonia disease symptoms on potato sprouts in greenhouse. in molecular examinations, the genetic similarity of 10 selected isolates was surveyed through rapd marker using 12 random primers. results of band patterns revealed that collected isolates from different geographical areas were placed in one clued with 100 percent genetic similarity. presence of high genetic similarity among isolates obtained from various geographical areas is an indication that the pathogen has distributed in these areas through sclerotia on infested potato seed tubers. therefore, considering the importance of r. solani ag-3, as the main agent of potato rhizoctonia disease in hamedan and kurdistan provinces and the long survival time of this fungus in soil, the transmission and planting of potato seed tubers covered with rhizoctonia sclerotia to new fields need to be prevented.