Field evaluation of lucerne (Medicago sativa L.) for resistance to aphids in northern China

Resistance of 9 lucerne cultivars and lines of predominantly overseas introductions to an aphid complex was evaluated in field experiments at Lanzhou city in Gansu province of northern China in 2004. The aphid complex, consisting of 3 aphid species, the spotted alfalfa aphid (SAA) Therioaphis trifolii Monell, black bean aphid (BBA) Aphis craccivora Koch, and pea aphid (PA) Acyrthosiphon pisum Harris, was found to be dominated by BBA at the early stage of plant growth in spring and by SAA at other stages. Plants infested by SAA showed the symptoms of either chlorotic leaf veins or yellow leaf. Cultivars performed similarly in Gansu as in their country of origin, with minor differences (e.g. Hunter River). ‘Aphid damage index’ and ‘% of resistant plants’ were found to be useful parameters for specifying the resistance of a given cultivar to the aphid complex. Based on the ‘% of resistant plants’, cvv. HA–3, Cropper 9, 8925MF, SARDI 7, and SARDI 10 were classified as highly resistant; HA–1 and Gannong 3, resistant; Jindera, moderately resistant; and Hunter River, low resistance.