Morphology and Viruslike Particle Content ofHelminthosporium victoriaeColonies Regenerated from Protoplasts of Normal and Diseased Isolates

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Abstract
Protoplast suspensions were prepared from cultures of 2 normal and 2 diseased isolates of H. victoriae [Victoria blight pathogen of oats]. Protoplasts from the normal isolates regenerated and formed colonies morphologically identical to the original cultures. Colonies regenerated from protoplasts of diseased isolates were of 3 morphologically-distinct types: type 1, normal vigorous colonies with dense aerial mycelium; type 2, colonies resembling the original diseased cultures; and type 3, severely stunted colonies with very sparse aerial mycelium. Diseased isolates previously were reported to contain 2 distinct types of isometric viruslike particles (VLP) designated 145S (Svedberg units) and 190S VLP. Normal isolates, on the other hand, either were VLP-free or contained only the 190S VLP. The normal colonies, type 1, obtained from protoplasts of diseased isolates either were devoid of or contained only traces of 145S VLP. The 145S VLP content of mycelia from the diseased colonies (type 2 or 3) correlated directly with disease severity; the highest yields of 145S VLP were obtained from mycelia with the most pronounced disease symptoms. These results suggest that the 190S VLP is not deleterious to its host and that the 145S VLP are associated with the disease.