Resistance to the Spotted Alfalfa Aphid in Lahontan Alfalfa1

Abstract

All growth stages of Lahontan alfalfa demonstrated high resistance to the spotted alfalfa aphid, Pterocallidium sp. Antibiosis, as measured by reduced aphid survival and fecundity rates, and tolerance were the most important resistance mechanisms which contributed to Lahontan survival and satisfactory forage production under conditions which severely injured Caliverde, California Common 49 and African. In yield trials under heavy infestation conditions, Lahontan produced 289% of African, 359% of California Common 49, and 403% of Caliverde, based on dry forage from a single early season cutting. Lahontan parents C-84, C-89 and C-900 were unsatisfactory for sustained aphid development and reduction under warm summer conditions. The remaining 2 parents, C-901 and C-902 supported aphid reproduction and were classed intermediate. Plant injury appears to be partially due to a toxin which becomes systemic after injected by the aphid. Lahontan is apparently more tolerant to the toxin than other varieties tested.