Abstract
Pubescent plants selected from PI 406295 (PIs) and a pubescent selection from ‘San Pedro’ (SP) alfalfa, Medicago sativa L., were used to determine the effects of simple hairs on resistance to the spotted alfalfa aphid (SAA), Therioaphis maculate (Buckton). Two resistant commercial cultivars, ‘Baker’ and ‘Dawson,’ and a susceptible cultivar, ‘Buffalo,’ were used as control entries. Uninfested seedlings of all entries showed consistent growth throughout an 18-d test period. Under SAA infestation, the PIs initially exhibited resistance and grew faster than the other entries but appeared less resistant 16 d after seeding. The susceptible control cultivar and SP rapidly died from SAA injury. Fecundity of SAA reared on seedlings and mature PI plants was significantly less than that on SP and ‘Buffalo’ but greater than that on the resistant lines. Preference for the PI plants was similar to that on the resistant control entries. Trichomes did not appear to be involved in the SAA resistance of the PIs, because the PIs and SP had equal numbers of trichomes but differed greatly in SAA resistance. We speculated that seedling vigor and some degree of antibiosis were responsible for SAA resistance in the PIs.
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