Characterization of molecular variability in Rhizoctonia solani isolates from different agro-ecological zones by random amplified polymorphic DNA (RAPD) markers

Rhizoctonia solani is a plant pathogenic fungus which is the causal organism of sheath blight of rice. Yield losses due to the sheath blight, caused by R. solani Kuhn is reported to range from 5.2 to 50%, depending on environmental conditions, crop stages at which the disease appears, cultivation practices and cultivars in India. Rice sheath blight has become a major constraint to rice production during the last two decades. In India, breeding for sheath blight resistant cultivars has been a priority area of research. Sheath blight disease caused by R. solani Kuhn was first recorded as minor disease of rice in West Bengal (a major rice growing province of India), later the disease was referred to as a major one in West Bengal, probably second only to blast in its crop damage potential. The present work was done to assess the molecular variability in 22 isolates of sheath blight fungus, collected from four different ecological regions of West Bengal, ranging from coastal, alluvial, red-lateritic to terai belts using random amplified polymorphic DNA (RAPD) markers. A total of 267 reproducible and scorable polymorphic bands ranging approximately as low as 200 bp to as high as 1500 bp were generated with eight RAPD primers. The similarity values of RAPD profiles ranged from 0.41 to 0.94 with an average of 0.67 among all the isolates. Most of the isolates collected from similar agro-ecological location clustered together in the present study. Our results indicate high genetic variability in the pathogen population in different epidemiological regions of West Bengal. Our study also reveals host-specific banding profile for the two isolates RS21 and RS22, which were collected from cabbage and were confirmed to belong to anastomosis group 4 (AG4).Key words: Rhizoctonia solani, rice, molecular variability, randomly amplified polymorphic DNA