Studies on alfalfa mosaic virus and alfalfa aphids

Abstract

Alfalfa mosaic virus (AMV), the only sap-transmissible virus detected in a limited survey of lucerne crops in New South Wales and the Australian Capital Territory, is more common and widespread now than 10 years ago. Twenty-four of 35 lucerne crops and test plots we sampled were infected; from 25 % to over 55 % of plants were infected in plots and crops at Ginninderra, A.C.T. Seven of 10 commercial lucerne seed lots (eight of them imported directly from the U.S.A.) contained seedborne AMV, which infected from 0.4 to 1.9% of seedlings. The three lucerne aphids, the bluegreen aphid (Acyrthosiphon kondoi), pea aphid (A. pisum) and the spotted alfalfa aphid (Therioaphis trifolii f. maculata), all transmitted AMV in the non-persistent manner. Feeding-preference tests indicate that spotted alfalfa aphids prefer to feed on AMV-infected Siriver lucerne than on healthy Siriver, but they do not discriminate between healthy and AMV-infected Hunter River lucerne. The implications of these results are discussed.