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Etiology

Association of Double-Stranded RNA with Low Virulence in an Isolate of Leucostoma persoonii. Sue Hammar, Graduate research assistant, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824; D. W. Fulbright, and G. C. Adams. Associate professor, and Assistant professor, respectively, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824. Phytopathology 79:568-572. Accepted for publication 4 January 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/Phyto-79-568.

Nine segments of double-stranded RNA (dsRNA) were identified in an isolate of Leucostoma persoonii (14.4A) demonstrating low virulence, abnormal culture morphology, and an inability to produce pycnidia when grown on culture media. Treatments of isolate 14.4A that altered the number of dsRNA segments also changed the virulence and morphology of the resulting cultures. When all dsRNA segments in isolate 14.4A were eliminated, the resulting cultures had increased virulence, sporulated, and grew similar to typical isolates of L. persoonii. Four segments of dsRNA were transferred by hyphal anastomosis from isolate 14.4A to a genetically marked strain. Based on dsRNA segment elimination patterns and dsRNA tranfer data, isolate 14.4A may be infected with at least two distinct dsRNA viruses.

Additional keywords: Cytospora, hypovirulence, mycovirus, Valsa, viruslike particle.