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Etiology

A New Vascular Wilt Disease Caused in Crimson Clover by Fusarium oxysporum. R. G. Pratt, Research plant pathologist, U.S. Department of Agriculture, Agricultural Research Service, and Department of Plant Pathology and Weed Science, Mississippi State University, P.O. Drawer PG, Mississippi State 39762; Phytopathology 72:622-627. Accepted for publication 31 August 1981. 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, 1981.. DOI: 10.1094/Phyto-72-622.

Crimson clover (Trifolium incarnatum) plants with stunted, chlorotic, and necrotic foliage and discolored vascular systems were observed in three fields in Mississippi. Fusarium oxysporum was isolated from symptomatic root tissue; few other fungi were obtained. Vascular wilt symptoms were reproduced in roots and crowns of plants grown in the greenhouse 4–6 wk after roots were inoculated with blended cultures, infested mixtures of cornmeal and sand, or suspensions of conidia. F. oxysporum was reisolated from roots and crowns of most symptomatic plants. It was also reisolated from flowering stems 12 wk or more after roots were inoculated. Mortality and severe foliar symptoms usually occurred only in plants inoculated in early spring and grown under increasing day lengths. Five isolates of F. oxysporum differed in virulence, but all caused wilt symptoms and death of some plants. Five cultivars of crimson clover differed slightly in susceptibility. No symptoms developed in alsike, arrowleaf, berseem, red, subterranean, or white clovers inoculated with F. oxysporum from crimson clover. Few or no wilt symptoms developed in crimson clover inoculated with F. oxysporum isolates from alfalfa, bean, cowpea, pea, or soybean, and isolates from clover caused few or no symptoms in those species. Results indicate that the wilt-inducing isolates of F. oxysporum from crimson clover are specialized in virulence to that host.