Genetic Diversity of Double-Stranded RNA fromRhizoctonia solani

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Abstract
Genetic relationships among double-stranded RNA (dsRNA) components from 42 isolates of the basidiomycete Rhizoctonia solani were examined by Northern blot hybridization. Isolates from five anastomosis groups (AG) representing a wide range of virulence were included in the study. There exists a relatively high degree of genetic heterogeneity among dsRNAs from a single isolate or isolates from the same AG. Results from several RNA-RNA hybridization experiments revealed a lack of genetic relatedness among dsRNA populations from different AGs. Cross-hybridization did occur, however, among dsRNA segments from three hypovirulent isolates belonging to AG 2, 3, and 5. Evidence presented here confirms findings of earlier reports as to the ubiquitous presence of dsRNA in R. solani, irrespective of degree of pathogenicity. Given the genetic diversity of dsRNAs occurring in this plant pathogen, our data provide no support for broad generalizations made in the past as to the association of dsRNA with virulence or hypovirulence in R. solani. In contrast, there appears to be a direct or indirect correlation between specific dsRNA species and hypovirulence.