Comparative Responses of Selected Cultivars of Four Annual Clover Species to Sclerotinia trifoliorum at Different Inoculum Levels in the Field. R. G. Pratt, Research Plant Pathologist, U.S. Department of Agriculture, and Departments of Plant Pathology and Weed Science and of Agronomy, Mississippi State University, Mississippi State 39762. W. E. Knight, Research Agronomist, Agricultural Research Service, U.S. Department of Agriculture, and Departments of Plant Pathology and Weed Science and of Agronomy, Mississippi State University, Mississippi State 39762. Plant Dis. 68:131-134. Accepted for publication 10 August 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, 1984. DOI: 10.1094/PD-68-131.

Six cultivars and one experimental line of annual clovers, representing four species, were grown in field plots at Mississippi State during three winter growing seasons. Sclerotia of Sclerotinia trifoliorum were added to soil at densities of 0, 20, 60, and 100 per plot (0.36 m²) in September of each year. Disease severity and forage yields were evaluated by observing symptoms and determining foliar dry weights of surviving plants in March. Symptoms differed among the species and were most severe in berseem and crimson clovers. Symptoms were progressively less severe in arrowleaf and subterranean clovers. Differences in yields usually corresponded inversely to severity of symptoms, but they also reflected differences in growth habits and sensitivity to freezing injury among species and cultivars. Yields of berseem clover were the lowest whenever Sclerotinia infection and freeze damage occurred together. Yields of Tibbee crimson clover were among the highest when disease was absent or slight but were often surpassed by yields of subterranean clover when disease was moderate or severe. Overall disease severity was greatest at the highest inoculum levels each season but varied greatly among seasons.

Keyword(s): Trifolium alexandrinum, T. incarnatum, T. subterraneum, T. vesiculosum.