Reduction of incidence of three persistently transmitted aphid-borne viruses affecting legume crops by seed-treatment with the insecticide imidacloprid (Gaucho®)

The effectiveness of using seed treatment with imidacloprid (Gaucho®) to reduce the incidence of Bean leaf roll virus (BLRV, family Luteoviridae), Faba bean necrotic yellows virus (FBNYV, genus Nanovirus) and Soybean dwarf virus (SbDV, family Luteoviridae) in faba bean and lentil was investigated, using artificial inoculation with an aphid vector, Acyrthosiphon pisum (Harris). Imidacloprid was applied as a seed dressing at the rate of 0.0, 0.35, 0.7, 1.4 and 2.8 g a.i./kg of seeds. Incidence of BLRV, FBNYV and SbDV in faba bean was reduced from 92, 28 and 98% in untreated plots to 23, 2 and 85% in plots treated with 1.4 g a.i./kg and 13, 1 and 85% in plots treated with 2.8 g a.i./kg, respectively. Moreover, the yield loss was reduced from 80, 37 and 56% in untreated plots to 14, 0 and 39% in plots treated with 1.4 g a.i./kg, and to 14, 0 and 34% in plots treated with 2.8 g a.i./kg, for the above three viruses, respectively. Results indicated that imidacloprid at 2.8 g a.i./kg reduced virus incidence in faba bean plants when they were inoculated with BLRV two months after sowing from 91.6% in untreated plots to 0%, but no effect was detected when virus inoculation was done three months after sowing. Moreover, imidacloprid seed treatment significantly improved lentil yields of moderately resistant and susceptible lentil genotypes, but had no effect on the yield of resistant genotypes. In addition, seed treatment was more effective in increasing seed yield of BLRV and FBNYV-inoculated plots compared to SbDV-inoculated plots. Based on these results, seed treatment with imidacloprid at 1.4 g a.i./kg of seeds can effectively reduce the incidence of two persistently transmitted aphid-borne viruses, BLRV and FBNYV, affecting faba bean and lentil crops.