Effects of aphids on seedling growth of lucerne lines. 2. Spotted alfalfa aphid (Therioaphis trifolii f. maculata (Monell)) in field conditions

Abstract

Seedlings of 23 lucerne lines introduced from the USA, and 2 Australian cultivars (Hunter River and Falkiner), were screened for resistance to the spotqed alfalfa aphid (Therioaphis trifolii f. maculata (Monell) (SAA) under field conditions during summer. This was assessed by measuring changes in plant mortality and yields from surviving plants in plots infested with SAA at the unifoliate leaf stage, compared, over a period of 19 days, with controls sprayed with insecticide. Cultivar Hunter River was extremely susceptible to SAA. It was the only line in which all seedlings died. Cultivar Falkiner was relatively susceptible, but no more so than 12 imported lines. Seven imported lines (WL 508, WL 512, WL 514, WL 600, CUF 101, UC Cargo and PS 572, all of which are known to be winter-active) exhibited greater resistance than the others. There was no association between the total number of SAA carried and their seedling resistance among the imported lines.