Pathogenic and Genetic Diversity among Iranian Isolates of Macrophomina phaseolina

charcoal rot, caused by macrophomina phaseolina (tassi) goid., is an economically important disease of oilseed plants in northern iran. seventy isolates of m. phaseolina were obtained from different hosts, including soybean (glycine max l.), and sunflower (helianthus annuus l.) in the northern oilseed planting regions of iran. rapd-pcr amplification profiles, by using of six random opa primers (kit a) showed polymorphisms among the isolates. the primer opa-13 (5'_ cagcacccac_3') amplified the genomic dna of all isolates of m.phaseolina producing 4-12 bands of sizes between 0.25 and 2.3 kb. unweighted pair-group method with arithmetic mean (upgma) analysis classified the isolates into the nine major groups with 64% similarity. pathogenicity of isolates was evaluated at seedling stage of soybean, sunflower, and maize (zea mays l.) plants under in vitro conditions. none of the isolates were pathogenic on corn, while all of the isolates infected soybean and sunflower seedlings. isolates were more virulent on soybean than sunflower. the disease index on sunflower and soybean varied between 19-24 and 27-30 respectively. these results indicated a significant pathogenic and genetic variability within the iranian isolates of m. phaseolina. cultivation with crop rotation was probably tended to induce less diversity of the pathogen isolates.