Double‐stranded RNA: distribution and analysis among isolates of Rhizoctonia solani AG‐2 to ‐13

The occurrence, distribution, and genetic relatedness of double‐stranded RNA (dsRNA) components from 36 isolates of Rhizoctonia solani belonging to nine anastomosis groups (AGs) were studied using electrophoretic analysis and RNA–RNA blot hybridization. DsRNA was consistently detected in all 36 isolates. The size of the dsRNA components varied considerably, ranging from 0·74 to 23 kb. Two thirds of isolates possessed different size dsRNA components. Only two of the isolates had small size dsRNA between 0·5 and 1·0 kb. The biotin‐labelled dsRNA probes provided the sensitivity and specificity required to study genetic relationships of dsRNA. As little as 10 pg of ‘hybridizing’ dsRNA could be detected using biotin‐labelled total dsRNA with no detectable nonspecific‐hybridization. Results from several dot‐spot as well as RNA–RNA gel hybridization experiments revealed considerable sequence heterogeneity among dsRNA components within each isolate or isolates from the same AG.