Various viral genomes from plant pathogenic fungi have been reported. The most common of these genomes found are dsRNA which in some fungi are associated with hypovirulence and have been used or proposed as biological control agents. In this study 33 Iranian isolates of Fusarium graminearum, were examined for dsRNA infection. In 12 of these isolates, more than three viral fragments measuring 0.9, 1.2, 3, 3.2 and 5 kb were detected. The presence and nature of dsRNA was confirmed by RNaseA and DNaseI treatments. To obtain dsRNA-free isolates, hyphal tip cultures of six isolates were transferred to PDA containing different concentrations of cycloheximide. Three hyphal tip cultures were confirmed to be dsRNA-free. Mycelial growth in dsRNA-containing isolates was less than that of their counterpart cured isolates with no dsRNA. Meanwhile, no significant difference was observed for colony morphology, pigmentation and conidia production of viruliferous and cured isolates. However, the disease severity of the dsRNA-containing isolates was significantly (p < 0.01) less than that of the dsRNA-free isolates on susceptible wheat in greenhouse. Deoxynivalenol (DON) production by dsRNA-free and dsRNA-containing isolates was confirmed using HPLC analysis. The range of DON production levels for dsRNA-free and dsRNA-containing isolates varied from 0.07 to 1.6 ppm and 0.06-0.4 ppm, respectively. A very significantly reduced level of DON, up to 50%, was detected in dsRNA-containing derivatives compared to the dsRNA-free isolates.
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