Seedling resistance to pea aphid of lucerne, annual medic and clover species in Victoria

Twenty-two lines of lucerne, six of annual Medicago spp., seven of Trifolium subterraneum, six of T. repens and six of several other Trifolium spp. were tested for seedling resistance to pea aphid, Acyrthosiphon pisum (Harris), in glasshouse tests at Burnley, Victoria. In general, lucerne cultivars selected for resistance to North American biotypes of the aphid were resistant to the Victorian aphid population. However, in our tests, two cultivars (Matador and Pioneer Brand 545) that were classed as susceptible to pea aphid in the USA. were as resistant as WL 31 8, a cultivar selected in the U.SA. for resistance to pea aphid. Medicago truncatula cvv. Borung and Cyprus were highly susceptible to pea aphid. They were more severely damaged than M. sativa cv. Hunter River, which was the most susceptible of the lucerne cultivars tested. M. rugosa cv. Paragosa had a high level of resistance while M. truncatula cvv. Hannaford and Jemalong, and M. littoralis cv. Harbinger were stunted but had only a low level of seedling mortality. Of the seven cultivars of T. subterraneum tested, only cv. Clare had a high level of aphid resistance, and all lines of T. repens were susceptible. The lines of T. fragiferum, T. incarnatum and T. pratense were more resistant than the susceptible check, T. subterraneum cv. Daliak, and should at least be tolerant in the field.