Resistance of cowpea (Vigna unguiculata L. Walp) cultivars to single and single double infections with Potyvirus and Sobemovirus isolates

Abstract

Cowpea (Vigna unguiculata) is a staple food in sub-Saharan Africa. However, diseases induced by Cowpea aphid-borne mosaic virus (CABMV; Potyvirus) and Southern bean mosaic virus (SBMV; Sobemovirus) cause significant yield losses. Cultivation of resistant cowpea varieties remains the most effective and sustainable management approach to these viruses. Eight cowpea cultivars were evaluated for CABMV, SBMV, CAMBV+SBMV, and SBMV+CABMV resistance in Minna, Southern Guinea Savanna of Nigeria during the 2016 cropping season. Virus infected and control plants were evaluated independently using a randomised complete block design with three replicates. In single infections, cowpea seedlings were inoculated at 10 days after sowing (DAS) while in double infections the second virus inoculation was performed at 21DAS. Disease incidence, symptom severity and seed weight per plant were recorded. The data were subjected to analysis of variance and Duncan Multiple Range Test was used for means separation. One hundred percent infection was obtained regardless of the cultivar. Moderate tolerance (symptom score = 3.0) was found only in IT10K-973-1 to CABMV, IT07K-298-9 and IT10K-817-7 to SBMV, and in IT07K-298-9, IT10K-817-7 and IT10K-973-1 to SBMV+CABMV. Seed weight per plant was significantly (p<0.05) highest in the healthy plants of IT10K-843. In virus infected, seed weight per plant was significantly highest in IT10K-843 (3.0 g) infected with CABMV; IT07K-298-9 (1.9 g) inoculated with SBMV, IT10K-973-1 (2.6) under CABMV+SBMV infections; and in IT07K-299-6 (3.0 g) infected with SBMV+CABMV. The cowpea cultivars IT10K-843 and IT10K-973-1 which produced appreciable yield under single and double virus infections are recommended to cowpea farmers.