Evaluation of selected cowpea (Vigna unguiculata L. Walp) genotypes for resistance to Cowpea aphid- borne mosaic virus disease

Abstract

Cowpea (Vigna unguiculata), is one of the most important and versatile nutritive grain legume crops native to Africa. However, disease induced by Cowpea aphid-borne mosaic virus (CABMV; Potyvirus) causes significant yield losses. Adoption of cultivars with inherent genetic resistance is the most effective and sustainable management option to limit the effect of pathogen.Twenty-four cowpea genotypes were evaluated under screenhouse conditions for resistance to CABMV disease. The experiment was laid out in completely randomised design with three replications. Seedlings were mechanically inoculated with virus extract at 10 days after sowing. Observations were made on percentage disease incidence, symptom severity, days to flowering, number of pods per plant, pod length per plant and number of seeds per pod. The data were subjected to analysis of variance and Duncan Multiple Range Test was used for means separation. All the cowpea genotypes infected with CABMV showed mosaic, vein yellowing and leaf deformation symptoms. Disease incidence varied from 11.1 to100 % at 3 weeks after inoculation (WAI). The cowpea genotypes: 11D-24-25 (symptom score = 1.3), 99K-573-2-1 (symptom score = 2) and IT12K-425 (symptom score = 2) exhibited the mildest disease severity. The cowpea genotype IT12K-425 combined low symptom expression with the highest seed production (9 seeds per pod). However, the genotype IT12K-488 also combined high number of pods (3 pods per plant) and seed (10 seeds per pod) production attributes. Therefore, IT12K-425 and IT12K-488 which were the most promising under CABMV infection are recommended for further evaluations and possible candidate for release for commercial production.