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Effect of Common Leafspot on Coumestans and Flavones in Alfalfa¹

The coumestan and flavone content of ‘Atlantic’ and ‘Cayuga’ alfalfa (Medicago sativa L.) was determined after infection with Pseudopeziza medicaginis (Lib.) Sacc., the common leafspot organism. A fluorometric assay on one- and two-dimensional paper chromatograms was used to determine six phenolic compounds.

Uninoculated checks contained less than 2 ppm ofcoumestrol and trace amounts of medicagol + 4'-Omethylcoumestrol and 7,4'-dihydroxyflavone. Samples collected 12 days after infection had significant amounts of all compounds studied except 3'-methoxycoumestrol. Samples collected 18 days after infection showed increases of from about 2 to over 11 times the concentrations found in the 12-day samples. The greatest increase from the 12-day to the 18-day samples was of sativol in both alfalfa varieties. However, accumulation of the phenolics was greatest in the more disease-susceptible variety Atlantic.

A similar set of samples infected with the alfalfa rust organism, Uromyces striatus Schroet, var. medicaginis (Pass.) Arth., was too low in coumestan and flavone content to obtain meaningful information. Rust urediospores contained large amounts of coumestrol and other coumestans, and the loss of urediospores by spore discharge before the late sampling date is assumed to have been the cause of the extremely low coumestan content in the rust samples.

Key Words: estrogens • phenolics • fluorometric • infected • rust • urediospores

² Principal Chemist, Assistant Chemist, and Associate Chemist, respectively, Western Regional Research Laboratory, Western Utilization Research and Development Division, ARS, USDA, Calif.

³ Research Agronomists at Brookings, S. D., and Beltsville, Md., respectively, and formerly Plant Pathologist, U. S. Regional Pasture Research Laboratory, University Park, Pa., Crops Research Division, ARS, USDA.

Received for publication December 31, 1966.