Ultrastructure of Plasmopara halstedii containing virus-like particles

Abstract

Mycoviruses have been found in more than 100 species of fungi and it is estimated that they may occur in as many as 500 species (Buck, 1986; Hollings, 1978; and Lemke, 1981). Mycoviruses range in size from small, isometric particles (25 nm in diameter) to long, flexuous rods exceeding 2000 nm in length, with the majority being isometric particles ranging in size from 25-50 nm (Buck, 1986). Mycoviruses hae been reported in all groups of fungi, but have been least frequently observed in the Oomycetes.Sunflower (Helianthus annuus) seedlings were inoculated with a North Dakota isolate of race 2 Plasmopara halstedii, the causal agent of sunflower downy mildew. Systemic disease symptoms developed within 14 days and samples were prepared for transmission electron microscopy using standard techniques.