FIELD AND LABORATORY SELECTION OF MEDICAGO PLANT INTRODUCTIONS FOR RESISTANCE TO THE CLOVER ROOT CURCULIO (COLEOPTERA, CURCULIONIDAE)

Taproots of Medicago sativa L. plant introductions grown in field nurs eries for 2 yr were evaluated for injury by larvae of the clover root curculio, Sitona hispidulus (F.). Most plants had approximate to 20-25 % of the taproot surface injured by larvae, but PI 183060 and PI 18326 3 averaged < 10%. Half-sibling progenies of plants with < 10% taproot injury were infested with clover root curculio eggs in the laboratory and grown in cone containers for 5 wk. Significantly less taproot inju ry was found on PI 183060, PI 183263, and PI 183404, and larval surviv al was lower on PI 315456-3, compared with the control. Half-sibling p rogeny and hand-pollinated crosses of other plant introductions that h ad low amounts of tap root feeding were seeded in an advanced nursery. Progeny of PI 464719 x PI 445871 had significantly less taproot injur y than the control. Choice tests for antixenosis to adult feeding on I st trifoliate in the greenhouse showed that PI 494661 and PI 516906 ha d significantly less feeding than the control. Overall, there was no c orrelation between adult feeding in the greenhouse and larval injury t o the taproot in the held. Evaluating alfalfa plant introductions in t he field for 2 yr followed by evaluation of their half-sibling progeni es is a useful strategy for identifying sources of resistance to tapro ot injury by the clover root curculio.