Growth and Yield Variability in Cowpea (Vigna unguiculata L. Walp.) Cultivars Infected with Cowpea Aphid-Borne Mosaic Virus and Southern Bean Mosaic Virus

Eight cowpea (Vigna unguiculata L. Walp.) cultivars were evaluated for Cowpea aphid-borne mosaic virus (CABMV), Southern bean mosaic virus (SBMV), CABMV+SBMV, and SBMV+CABMV resistance under screenhouse conditions at the School of Agriculture and Agricultural Technology Minna, Nigeria in 2016 (lat.9o40ʹN; long 6o30ʹE at an altitude of 220m.a.s.l). Virus infected plants were evaluated independently using a Completely Randomized Design with three replications. In single infections, cowpea seedlings were inoculated at 10 days after sowing (DAS) while in mixed infections the second virus inoculation was performed at 21 DAS. Disease incidence, symptom severity, plant’s growth and yield characters were recorded. The data were subjected to analysis of variance and Duncan’s Multiple Range Test was used for mean separation. Results showed that one hundred percent infection was obtained regardless of the cultivar. High disease severity with the symptom score of 4.0 was recorded for all the cowpea cultivars infected with CABMV alone and CABMV+SBMV, while moderate resistance with a symptom score of 3.0 was recorded only in cultivars IT09K-231-1 and IT10K-973-1 to SBMV, and in IT07K-299-6 and IT10K-973-1 to SBMV+CABMV. Through the four virus treatments, seed weight per plant was significantly (p<0.05) highest in IT10K-843 infected with CABMV which produced 3.5 g; cultivar, IT07K-299-6 inoculated with SBMV produced 4.9 g, while IT10K-973-1 under CABMV+SBMV infections produced 4.9 g; and IT07K-298-9 infected with SBMV+CABMV produced 4.4 g. The cowpea cultivar IT07K-299-6 which gave the highest seed weight under single and double virus infections can be exploited in hybridization studies to develop resistant cowpea varieties for use by farmers.