Effects of different cultural practices on spread of cucumber mosaic virus in narrow-leafed lupins (Lupinus angustifolius)

Abstract

Lupinus angustifolius (narrow-leafed lupin) was sown in 7 field experiments to examine the effects of cultural practices on incidence of cucumber mosaic virus (CMV). The factors investigated were row spacing, banding fertiliser below seed, straw groundover, and tillage. The seed sown carried 5–15% CMV infection. Seed-infected plants were the primary source for subsequent virus spread by aphids. Incidence of seed-infected plants and the extent of virus spread were gauged by counting numbers of lupin plants showing typical seed-borne and current-season CMV symptoms. Due to greater competition with other plants within wide than narrow rows, wide row spacing diminished the survival of seed-infected plants by 46%. Increased plant growth from banding superphosphate below seed did not significantly decrease numbers of seed-infected plants surviving. Straw spread on the soil surface suppressed final CMV incidence by 25–40% and, when applied at different rates, diminished recorded CMV incidence more at 4 than 2 t/ha and least at 1 t/ha. Where there was no straw, CMV incidence increased faster with narrow spacing than wide spacing. Soil disturbance from sowing seed with double discs instead of tynes significantly increased incidences of both seed-borne and current-season infection and diminished grain yield. Neither straw nor row spacing treatments significantly affected grain yield, but the decrease in CMV spread due to straw ground cover significantly increased individual seed weight once and overall yields were greater with straw. Myzus persicae was the main colonising aphid species but Aphis craccivora and Acyrthosiphon kondoi also colonised the lupins. There were significantly fewer colonising M. persicae in plots with 4 t/ha of straw than in those with none. This work suggests that stubble retention, minimum tillage, and wide row spacing should be included as components of an integrated disease management strategy for CMVin L. angustifolius crops.