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Virulence Differences Between Fusarium roseum ĎAcuminatumí and F. roseum ĎAvenaceumí in Red Clover. J. C. Stutz, Graduate assistant, Department of Plant Pathology, Pennsylvania State University, University Park 16802, Current address of senior author: assistant professor, Division of Agriculture, Arizona State University, Tempe 85287; K. T. Leath, adjunct professor, Department of Plant Pathology, Pennsylvania State University, University Park 16802, also a research plant pathologist, USDA-ARS. Phytopathology 73:1648-1651. Accepted for publication 22 June 1983. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1983. DOI: 10.1094/Phyto-73-1648.

The virulence of isolates of Fusarium roseum ĎAcuminatumí was compared to that of isolates of F. roseum ĎAvenaceumí in roots of 5-wk-old red clover plants and also in red clover seedlings. Penetration and colonization of roots by isolates of the two pathogens were observed. In 5-wk-old plants, isolates of F. roseum ĎAvenaceumí were more virulent than isolates of F. roseum ĎAcuminatumí and caused more frequent and severe necrosis at all inoculation sites above the root tip. There were distinct differences in fungal development between the two pathogens in roots of 5-wk-old plants inoculated at least 2 cm from the root tip. F. roseum ĎAvenaceumí colonized the cortex via distributive hyphae, and caused necrosis in this area. F. roseum ĎAcuminatumí penetrated the epidermis in this area, but further colonization was limited to the formation of chlamydospores in the cortex. Neither distributive hyphae nor necrosis was observed. When 5-wk-old plants were inoculated at the root tip, both pathogens penetrated and colonized the root, formed distributive hyphae and caused necrosis. In inoculated seedlings, there were no differences in virulence between isolates of F. roseum ĎAcuminatumí and ĎAvenaceumí as measured by frequency and length of necrosis. Both pathogens formed distributive hyphae in the cortex of seedling roots.