COMPARISON OF DOUBLE-STRANDED-RNA COMPONENTS AND VIRULENCE AMONG ISOLATES OF RHIZOCTONIA-SOLANI AG-1 IA AND AG-1 IB

Double-stranded RNA (dsRNA) was detected in 22 of 35 (63%) Rhizoctonia solani anastomosis group one (AG-1) intraspecific groups IA and IB isolates screened. Most AG-1 IA isolates had seven dsRNAs with molecular sizes ranging from 1.3 to 9.3 kb, whereas most AG-1 IB isolates had a 12-kb dsRNA. Not all isolates of AG-1 IA or IB obtained from the same soybean field had dsRNA. The dsRNAs were stable through six successive subculturings. Cell fractionation of R. solani revealed that dsRNAs were located in the microsomal fraction. The dsRNAs were no longer detected in two isolates of AG-1 IB and one isolate of AG-1 IA after 1 wk of growth at 35 C; however, the dsRNAs of one isolate of AG-1 IA were not lost at 35 C. The presence or absence of dsRNA in R. solani AG-1 IA or IB isolates did not correlate with virulence, mycelial growth, or phenol oxidase activity of the isolates. Extensive variation in the electrophoretic patterns of dsRNA was observed among the isolates of R. solani belonging to AG-1 IC, AGs-2, -3, -4, -5, and -7, and AG-BI. The dsRNA fingerprints of these anastomosis groups differed from those of AG-1 IA and IB.