MECHANISMS OF RESISTANCE TO THE POTATO LEAFHOPPER (HOMOPTERA, CICADELLIDAE) IN SELECTED ALFALFA CLONES

Selected clones of alfalfa, Medicago sativa L., from three populations ('Arc', B16, and Indiana Syn C) were subjected to free and no-choice laboratory and field tests to identify specific mechanisms of resistance to potato leafhopper, Empoasca fabae (Harris). Initial selection of clones used in this study was based on seedling survival under heavy potato leafhopper adult feeding pressure. In addition to those mechanisms of resistance associated with dense pubescence in B16 clones (feeding and oviposition nonpreference and nymphal antibiosis), this study identified specific clones in 'Arc' and Indiana Syn C populations demonstrating feeding or oviposition nonpreference or both. A small but significant level of nymphal antibiosis also was identified in several 'Arc' clones. No clones that had an adverse effect on adult survival or development were identified. The identification of individual clones with moderate levels of feeding and oviposition nonpreference and nymphal antibiosis in laboratory tests under controlled conditions suggests that greater progress would be achieved in identifying resistant clones if initial and recurrent selection for these resistance mechanisms were stressed using individual plant selection rather than seedling selection.