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Flavones, Isoflavones, and Coumestans in Alfalfa Infected by Ascochyta imperfecta. Arthur F. Olah, Graduate Assistant, Department of Plant Pathology, North Carolina State University, Raleigh 27607, Present address of the senior author: Department of Biology, Frostburg State College, Frostburg, Maryland 21532; Robert T. Sherwood, Plant Pathologist, Crops Research Division, ARS, USDA, on assignment to Raleigh. Phytopathology 61:65-69. Accepted for publication 10 August 1970. DOI: 10.1094/Phyto-61-65.

Leaves and roots of healthy, chamber-grown Atlantic alfalfa plants, and of plants harvested daily for 7 days after inoculation with Ascochyta imperfecta, were assayed for flavonoid compounds. Glycosides of the following flavonoid compounds occurred in both healthy and infected leaves: formononetin, daidzein, 7,4’-dihydroxyflavone, 7,3’,4’-trihydroxyflavone, and tricin. As the leaf spots developed, the concentration of the flavonoid glycosides increased or remained unchanged. Flavonoid aglycones were not detected in healthy leaves. Aglycones were first detected in leaves 3-4 days after inoculation, and increased in concentration through the 7th day. These included formononetin, daidzein, 7,4’-dihydroxyflavone, 7,3’,4’-trihydroxyflavone, coumestrol, 7-hydroxy-11,12-dimethoxycoumestrol, 4’-0-methyl-coumestrol, sativol, and medicagol. Several additional fluorescent compounds, apparently flavonoid glycosides, were detected in healthy and infected leaves, but were not identified. Roots contained principally formononetin-glycoside and coumestrol-glycoside. Fewer flavonoid glycosides and aglycones were detected in roots than leaves. Infection of leaves by A. imperfecta did not alter the flavonoid contents of the roots. The results suggest that flavonoid pathways and constituents which occur in normal leaves may be involved in the formation of flavonoid estrogens and phytoalexins during pathogenesis.