Significance of dsRNA Genetic Elements in Plant Pathogenic Fungi

Phenotypic variability involving morphology, synthesis of secondary metabo­ lites, or virulence is not uncommon in filamentous fungi. Efforts to explain this phenomenon have stimulated interest in extrachromal genetic elements such as mycoviruses, plasmids, or transposons as modulators of fungal gene expression. DNA plasmids are not prevalent in filamentous fungi, and the incidence of transposable elements has only recently been reported (62). In contrast, mycoviruses and related double-stranded (ds) RNA genetic elements are found associated with fungi at a very high frequency. Consequently, the . contribution of these genetic elements to phenotypic variability has come under increased scrutiny. The first fungal viruses were isolated from mushrooms in 1962 (57), followed six years later by the discovery of viruses in Penicilliumfuniculosum