Levels of isoflavonoids as indicators of resistance of subterranean clovertrifoliates to redlegged earth mite Halotydeus destructor

The extracts, obtained with methanol from crushed trifoliates and from the surface layer of the trifoliates, contained isoflavones in both the free an d bound forms as the major components, compounds known to exhibit feeding d eterrence towards the redlegged earth mite. The levels of these compounds w ere quantified and showed considerable variation in extracts of one suscept ible variety and four varieties with differing levels of resistance. The re lative resistance of the five varieties established from field observations was compared with the amounts of isoflavone derivatives obtained in the tw o extracts. A better ranking of resistance was found with levels of isoflav ones on the leaf surface than with the total amount of isoflavones in the t rifoliates, These results suggest a simple method for determining the relat ive resistance of subterranean clover to the mite.