Further studies on cucumber mosaic virus infection of narrow‐leafed lupin (Lupinus angustifolius): seed‐borne infection, aphid transmission, spread and effects on grain yield

Abstract

SUMMARYFour field trials were done with narrow‐leafed lupins (Lupinus angustifolius) in 1988 ‐ 1989, to examine the effect of sowing seed with 5% and 0.5% cucumber mosaic virus (CMV) infection on subsequent virus spread, grain yield and percentage of infection in harvested seed. A proportion of the CM V‐infected seed failed to produce established plants and thus, plots sown with 5% and 0.5% infected seed contained 1.5‐2.9% and 0.2‐0.3% of seed‐infected plants respectively. The rate of virus spread by aphids was faster and resulted in more extensive infection at maturity in plots sown with 5% infected seed than with 0.5% infected seed. In three trials, sowing 5% infected seed resulted in yield losses of 34 ‐ 53% and CMV infection in the seed harvested of 6 ‐ 13%. The spread of CMV infection resulting from sowing 0.5% infected seed did not significantly decrease yield. However, late CMV spread in these plots caused > 1% seed infection. In the fourth trial, which was badly affected by drought, CMV spread only slowly, there was no significant effect of CMV on grain yield and the percentage of infected seed harvested was 3–5 times less than that in the seed sown.When CMV‐infected seed was sown at different depths, target depths of 8 and 11 cm decreased the incidence of seed‐infected plants by c. 15% and c. 50% respectively compared with sowing at 5 cm. However, in glasshouse tests, treatment with the pre‐emergence herbicide simazine failed to selectively cull out seed‐infected plants.The field trials were colonised by green peach (Myzus persicae), blue‐green (Acyrthosiphon kondoi) and cowpea (Aphis craccivora) aphids. When the abilities of these aphid species and of the turnip aphid (Lipaphis erysimi) in transmitting CMV from lupins to lupins were examined in glasshouse tests, short acquisition access times favoured transmission. With 5–10 min acquisition access times, overall transmission efficiencies were 10.8%, 9.4%, 6.1% and 3.9% for the green peach, cowpea, blue‐green and turnip aphids respectively.