Stem canker and black scurf of potato (Solanum tuberosum L.) caused by Rhizoctonia solani Kühn are important and epidemic diseases in potato-growing regions worldwide, including Iran. In this study, 120 isolates were retrieved from infected stem canker from six potato- growing regions in Iran (Isfahan, Ardebil, Fars, Hamedan, Kurdestan and Kerman). Out of these, 30 isolates were selected as representatives for genetic and virulence analysis. The isolates were analyzed by one sequence analyzes of the ITS-rDNA region, random amplified polymorphic DNA (RAPD) and inter-simple sequence repeat (ISSR), as well as virulence studies. Based on sequence analysis of the ITS-rDNA region, all 30 isolates were assigned to the anastomosis group (AG) and all were assigned to AG-3 PT. Cluster analysis using the unweighted pair group method with the arithmetic averages (UPGMA) method for both RAPD and ISSR markers revealed that they were divided into three main groups, with no correlation to geographical regions of the isolates. Pathogenicity tests showed that all isolates were pathogenic on potato cv. Agria; however, virulence variability was observed among the isolates. The grouping based on RAPD analysis and virulence variability was not correlated.

Potato leaf blight disease caused by Ulocladium atrum (Syn. Stemphylium atrum) is an important and epidemic disease in potato-growing regions of Iran. In this study, 30 isolates of the disease were collected from the main potato-growing regions of Iran and were analyzed on the basis of morphological characterization and pathogenicity. Based on morphological characteristics, all isolates were identified as U. atrum. Pathogenicity studies indicated that all 30 isolates were pathogenic on potato “Agria” to varying degrees. Five U. atrum isolates causing potato leaf blight disease, obtained from the Plant Pathology Laboratory, Isfahan Research Center for Agriculture and Natural Resources, Isfahan, Iran, were also examined in this study. A total of 35 isolates were genetically analyzed using random amplified polymorphic DNA (RAPD) and inter-simple sequence repeats (ISSR) markers. Cluster analysis using the un-weighted pair group method with the arithmetic average (UPGMA) method for RAPD marker revealed no clear grouping of the isolates obtained from different geographical regions. The groupings, based on morphological characteristics, virulence variability and RAPD analysis, were not correlated. Cluster analysis using Jaccard’s coefficient for ISSR divided the U. atrum isolates into four main groups, in which there was no significant correlation between the isolate groupings regarding their geographic location and pathogenicity. Using molecular techniques genetic variability was detected among the accessions, with cophenetic correlation coefficients (CCC) of 0.80 for RAPDs and 0.89 for ISSRs. The RAPD and ISSR marker results corresponded well, with a correlation of 0.55.