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Abstract
One hundred ten isolates of Macrophomina phaseolina, the causal agent of charcoal rot of many different plant species, were obtained from Mexico, Somalia, and several locations in the United States, and analyzed for the presence of double-stranded RNA (dsRNA). Twenty-one isolates from the United States and Mexico contained dsRNA elements. The sizes of the dsRNAs ranged from ca 0.4 kbp to 10 kbp and the number of dsRNAs present among the isolates ranged from one to ten. Attempts to detect virus particles by sucrose gradient centrifugation were unsuccessful. Three isolates having dsRNA and three dsRNA-free isolates were evaluated for virulence on sorghum at two different field locations and for mycelial growth in PDA and V8 agar. For both locations, the isolates that had dsRNA were significantly less virulent (P < 0.05) than the dsRNA-free isolates. Differences between locations were not significant (P < 0.05). The contrasts between means of isolates with and without dsRNA suggest a strong association between the presence of dsRNA and a reduction in both mycelial growth and the capacity to cause disease. These results suggest an association between the presence of dsRNA and hypovirulence in the fungus.