RNA virus in Allomyces arbuscula: ultrastructural localization during the life-cycle.

Strain Bali I of Allomyces arbuscula is infected with a RNA virus; strain North Carolina is not. The virus appears to be avirulent, for strain Bali I showed no signs of pathogenicity. Virus aggregates occurred mostly in the cytoplasm during different stages of the gametophytic and sporophytic generations. Small intra-nuclear aggregates were found only in differentiating gametophytic hyphae and immature gametangia. In motile cells (gametes and zoospores) the aggregates are exclusively contained within the nuclear cap. This represents a reliable mechanism of transmission throughout the life-cycle.