Twenty three (n=23) isolates of Rhizoctonia solani were obtained from root, crown and rhizosphere of cucumber, pumpkin, watermelon and melon plants. Investigation of the anastomosis groups (AGs) showed that all of the isolates belonged to AG4. Twenty three of R. solani AG4 were measured for disease severity according to their geographical origins and host plants. The pathogenicity test revealed that the disease severity varied from 8.3 to 91.6%, when all isolates were inoculated on their corresponding hosts. The disease severity indicated that R. solani isolates were classified into five groups. Genetic diversity was performed among isolates of R. solani AG4 by combination of random amplified polymorphic DNA (RAPD) and inter-simple sequence repeat (ISSR) techniques. Amplicon size of six RAPD primers out of fifteen and four ISSR primers out of ten, ranged from 0.5 to 3 Kb in isolates. All isolates were divided into seven groups at >30% similarity level. The results exhibited a high genetic variability in the R. solani AG4 population, without any correlation between genetic diversity, the host plants and geographical regions.
Key words: Cucurbits, genetic diversity, random amplified polymorphic DNA (RAPD), inter-simple sequence repeat (ISSR), pathogenicity, Rhizoctonia solani.
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