Spontaneous appearance of genetically distinct double-stranded RNA elements in Rhizoctonia solani

A tuberborne sclerotium of the plant-pathogenic basidiomycete Rhizoctonia solani gave rise to a culture (Rhs 1AP) that exhibited a sector (Rhs 1A1) with reduced pigmentation and growth rate. Rhs 1AP is virulent on potato, which is the only known host plant for Rhs 1AP. In contrast, Rhs 1A1 is hypovirulent or nonpathogenic on potato. The virulent isolate Rhs 1AP contains two double-stranded RNAs (dsRNAs) of 23 and 6.54 kb, whereas the hypovirulent Rhs 1A1 possesses three dsRNAs in addition to the two found in Rhs 1AP [...]