Formononetin in clovers as a feeding deterrent against clover root weevil

Abstract

The effect of leaf feeding by adult clover root weevils on the isoflavonoid content of red and white clovers was investigated in a glasshouse experiment. Lines of both clovers previously selected for variation in formononetin content were used. A higher percentage of white clover leaves than red clover leaves were damaged by the weevils, and the high formononetin red clover was least readily eaten. The formononetin content of the white clovers did not differ between the selections, was much lower than in the red clovers, and did not change in response to weevil feeding. In both red clover lines, formononetin and biochaninA levels rose in response to weevil feeding, suggesting that both compounds have antifeedant properties against clover root weevil. Because high foliar levels of oestrogenic compounds like formononetin threaten fertility of grazing sheep it is concluded that plant breeding programmes should increase the levels of formononetin and/or biochaninA in clover roots to mitigate the impact of weevil larval feeding on roots and nodules.