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Morphology and Viruslike Particle Content of Helminthosporium victoriae Colonies Regenerated from Protoplasts of Normal and Diseased Isolates. S. A. Ghabrial, Associate professor, Plant Pathology Department, University of Kentucky, Lexington, 40506; R. S. Sanderlin(2), and L. A. Calvert(3). (2)(3)Former graduate student, and research associate, respectively, Plant Pathology Department, University of Kentucky, Lexington, 40506, (2)Present address: Pecan Station, Louisiana State University, P.O. Box 5519, Shreveport, 77105. Phytopathology 69:312-315. Accepted for publication 25 September 1978. Copyright 1979 The American Phytopathological Society. DOI: 10.1094/Phyto-69-312.

Protoplast suspensions were prepared from cultures of two normal and two diseased isolates of Helminthosporium victoriae. Protoplasts from the normal isolates regenerated and formed colonies morphologically identical to the original cultures. Colonies regenerated from protoplasts of diseased isolates were of three 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 two distinct types of isometric viruslike particles (VLPs) designated 145S (Svedberg units) and 190S VLPs. Normal isolates, on the other hand, either were VLP-free or contained only the 190S VLPs. 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 VLPs 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 VLPs are associated with the disease.