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Fusarium Root Rot of Forage Species: Pathogenicity and Host Range. K. T. Leath, Research Plant Pathologist, Agricultural Research Service, U.S. Department of Agriculture (also Associate Professor of Plant Pathology, The Pennsylvania State University) U.S. Regional Pasture Research Laboratory, University Park, PA 16802; W. A. Kendall, Plant Physiologist, Agricultural Research Service, U.S. Department of Agriculture (also Professor of Agronomy, The Pennsylvania State University) U.S. Regional Pasture Research Laboratory, University Park, PA 16802. Phytopathology 68:826-831. Accepted for publication 29 November 1977 . Copyright 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-826.

The pathogenicity of Fusarium roseum, F. oxysporum, F. solani, and F. moniliforme, isolated from diseased roots of forage plants, was compared on eight forage species in nutrient solution culture. The fungi were grown on polyester cloth strips placed on V-8 juice agar, and these strips were used to inoculate individual roots. The length of rot, frequency of infection, and inhibition of root growth were used to rate pathogenicity. Root tips were more susceptible to attack by the Fusarium spp. than were areas 2 cm above the root tip. Some isolates of F. roseum did not cause rot symptoms except at the root tip. Roots inoculated at the root tip often ceased elongation before they were penetrated by the fungus. White clover and birdsfoot trefoil were the most susceptible to root rot caused by Fusarium spp.; orchardgrass and crownvetch were the most resistant; and alfalfa, red clover, subterranean clover, and Coronilla globosa were intermediate in susceptibility. Isolates of the four Fusarium spp. usually gave greater frequency of infection, linear extent of rot lesions, and inhibition of root growth on the host species from which they were originally isolated than on the other species tested. Stress treatments such as clipping, foliar disease, and darkness, reduced root growth but did not affect root rot development in red clover. The relative pathogenicity of isolates of F. roseum to plants grown in nutrient solution culture was confirmed by inoculations of severed taproots of 4-mo-old red clover and alfalfa plants in soil in the greenhouse.

Additional keywords: inoculation methods, Medicago sativa, Coronilla varia, Trifolium pratense, Trifolium repens, Trifolium subterraneum, Dactylis glomerata, Lotus corniculatus.