Effect of Aphid Infestation on the Coumestrol Content of Alfalfa Varieties Differing in Aphid Resistance1

Abstract

The effects of pea aphid and spotted alfalfa aphid infestations on the coumestrol content of three alfalfa (Medicago sativa L.) varieties and one alfalfa synthetic were determined in plant growth chambers. The alfalfas tested ranged from very susceptible to highly resistant to both aphid species. Coumestrol from aphid‐damaged tissue was identified by chromatography and ultraviolet spectroscopy. Aphid‐damaged portions of all varieties contained elevated coumestrol levels. Undamaged plant tissue and uninfested plants generally had less than 1 ppm coumestrol. The more resistant varieties accumulated less coumestrol than the susceptible variety ‘Vernal.’ Selection in alfalfa for aphid resistance can be expected to reduce the accumulation of coumestrol which results fiom aphid damage.