Resistance to the Spotted Alfalfa Aphid (Homoptera: Aphididae) in Glandular-Haired Medicago Species 1

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Abstract
We evaluated glandular-haired Medicago species [perennial tetraploid M. sativa L. subsp. praefalcata (Sinskaya) C. R. Gunn, annual diploids M. blancheana Boiss., M. disciformis DC, and annual tetraploids, M. rugosa Desr., and M. scutellata (L.) Mill.] for resistance to the spotted alfalfa aphid, Therioaphis maculata (Buckton), in growth chambers. Resistant and susceptible perennial M. sativa clones were used for controls. In free-choice tests, the glandular-haired species and the resistant M. sativa control clone were less attractive than the susceptible control clone. Very few aphids reproduced on M. disciformis . Fewer aphids were on the annuals than on the perennial glandular-haired species. When the aphids' choices were limited to the annual species M. scutellata and M. disciformis , they departed from both and moved around the arena. Similarly, when only the resistant M. sativa clone and M. scutellata were available, the aphids chose the arena over the plants. In no-choice tests under three temperature regimes, resistance of M. disciformis and the resistant M. sativa clone was similar. Resistance of M. blancheana , M. rugosa , and M. scutellata was similar and lower than that of M. disciformis . Resistance of the glandular-haired M. sativa clone was low, but rate of aphid reproduction and total nymphs produced on it were lower than on the susceptible control clone under a constant temperature of 24°C or under 29°C day-16°C night temperature regimes.

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