Multi-locational Screening of Genotypes of Cowpea [Vigna unguiculata (L) Walp] for Resistance to Viral Infection

Viral diseases are an important biotic constraint to cowpea production in sub-Saharan Africa. The use of resistant varieties is the most effective approach in managing viral diseases. In order to identify sources of resistance, thirty two cowpea genotypes were evaluated in field trials at coastal savannah, Sudan savannah and semi-deciduous forest agro-ecological zones of Ghana during 2015 major cropping season. The experiments were laid out in a randomized complete block design with four replications. Viral disease severity was assessed at 8 weeks after planting (WAP) based on 1-5 visual scale (1= no symptom, 5= very severe symptom). All the cowpea genotypes at the various locations showed symptoms of viral diseases but at varying degrees. However, the levels of incidence and severity were generally low and varied significantly (P<0.05) with locations, with forest zone having the highest incidence of 30.79%, and severity score of 1.354 whilst Sudan savanna zone had the lowest incidence of 5.62% and severity score of 1.036. Genotypes Apagbaala, UCC-366, UCC-473, UCC-484, UCC-489, UCC-490, UCC-497, UCC-514 and UCC-523 showed field resistance (mild symptoms) at all three agro-ecological zones. Genotype x location (GXL) interaction effects on mean incidence and severity were however, not significant (P>0.05). Results also showed significant differences among genotypes, locations and GXL interaction effects on plant height, canopy diameter, 100-seed weight and seed yields (P<0.05). Overall mean seed yield at UCC (5.25 t ha-1) was significantly higher than Bunso (1.186 t ha-1) and Bawku (1,188 t ha-1). Therefore genotypes that was resistant to viral infection and also gave high seed yields should be further evaluated and released as a variety for the locations where they performed better.