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Coumestrol Content of Alfalfa as Affected by Selection for Resistance to Foliar Diseases¹

Studies were conducted on changes in coumestrol content of alfalfa which occurred in each of two germ-plasm pools as a result of recurrent selection practiced previously for resistance to two foliar diseases, common leafspot (Pseudopeziza medicaginis (Lib.) Sacc.) and rust (Uromyces striatus Schroet. var. medicaginis (Pass.) Arth.). For each disease, plants of each selection cycle were established from remnant seed and inoculated under uniform, controlled conditions. Selection for increased resistance to common leafspot resulted in fewer leafspots and lower coumestrol content in plants of both pools. Coumestrol content was positively associated with lesion size and number. In the rust phase of the study, coumestrol content was also positively associated with lesion size and number except in the most susceptible class. Urediospores were high in coumestrol, a factor which suggested that the massive spore fall which occurred in very susceptible plants resulted in a loss of coumestrol in very susceptible individuals. Selection in alfalfa for resistance to common leafspot and rust can be expected to reduce the increase in coumestrol content which results from growing the crop under conditions favorable for development of these diseases.

Key Words: disease resistance • plant estrogen • common leafspot • rust

² Research Agronomists at Brookings, S. D., and Beltsville, Md., and formerly Plant Pathologist, U. S. Regional Pasture Research Laboratory, University Park, Pa., CRD, ARS, USDA.

Received for publication October 14, 1966.