VARIATION IN APHID ALARM PHEROMONE CONTENT AMONG GLANDULAR AND EGLANDULAR-HAIRED MEDICAGO ACCESSIONS

Pea (Acyrthosiphon pisum Harris) and blue alfalfa aphid (A. kondoi Shi nji) deterrency in alfalfa (Medicago sativa L.) may result from incorp orating higher levels of the aphid alarm pheromone, (E)-beta-farnesene relative to (E)-beta-caryophyllene. We evaluated five eglandular and two glandular-haired alfalfa accessions for differences in (E)-beta-fa rnesene and (E)-beta-caryophyllene content under glasshouse conditions using supercritical fluid extraction and gas chromatography, In addit ion, pea and blue alfalfa aphid olfactory behavioral tests were conduc ted upon Medicago species containing different ratios of (E)-beta-farn esene relative to (E)-beta-caryophyllene, No differences in (E)-beta-c aryophyllene content were observed among the seven entries (mu = 0.42 ng/g plant material). Significant differences (P less than or equal to 0.05) among entries were observed for (E)-beta-farnesene content, wit h KS94GH6 exhibiting the highest (1.18 ng/g), and CUF 101 the lowest l evels (0.35 ng/g). Elite tetraploid sources possessed significantly lo wer levels (mu = 0.42 ng/g) of (E)-beta-farnesene than did wild and cu ltivated diploid accessions (mu = 0.83 ng/g). Olfactory behavioral tes ts for both the pea and blue alfalfa aphids demonstrated KS94GH6 repel led aphids while cultivated alfalfa types attracted aphids in each cas e. Previously demonstrated aphid resistance in diploid KS94GH6 may res ult from superior (E)-beta-farnesene levels, but (E)-beta-farnesene is probably not a factor in cultivated alfalfa resistance. Finally, acce ssion KS94GH6 could act as an excellent germplasm resource for the inc orporation of higher (E)-beta-farnesene levels into cultivated alfalfa .