Fusarium Root Rot of Forage Species: Pathogenicity and Host Range

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Abstract
The pathogenicity of F. roseum, F. oxysporum, F. solani and F. moniliforme, isolated from diseased roots of forage plants, was compared on 8 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, infection frequency and root growth inhibition 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 [Trifolium repens] and birdsfoot trefoil [Lotus corniculatus] were the most susceptible to root rot caused by Fusarium spp.; orchardgrass [Dactylis glomerata] and crownvetch [Coronilla varia] were the most resistant; and alfalfa [Medicago sativa], red clover [T. pratense], subterranean clover [T. subterraneum] and C. globosa were intermediate in susceptibility. Isolates of the 4 Fusarium spp. usually gave greater infection frequency, 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.

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