Multi-location evaluation of yield and yield components of grain cowpea (Vigna unguiculata (L.) Walp.) grown in Southeastern Nigeria
An evaluation study was carried out on 14 cowpea genotypes grown across four locations representing different environments in southeastern Nigeria, namely, Umudike, Nsukka, Igbariam and Abakaliki. Differences among genotypes, locations and genotypes by location components of variation were highly significant (P<0.05) for all the traits studied. Cowpea genotype, IT98K-131-2 produced significantly higher grain yield in Umudike and Igbariam, and ranked second and third respectively, in Abakaliki and Nsukka locations. Genotypes IT84S-2246-4 and IT97K-1069-6 were the highest grain yielders in Abakaliki and Nsukka respectively, indicating specific adaptation. Analysis of variance and GGE biplot both revealed that IT98K-131-2 exhibited superior performance across the four testing environments. Most of the yield component traits such as number of pods per plant, 100 seed weight, pod weight, pod length, seed weight and grain yield were best expressed in Umudike while Abakaliki supported the highest expression of growth and reproductive traits. No trait was particularly best expressed in Igbariam and Nsukka locations except dry fodder weight that was well expressed in Igbariam. Umudike and Abakaliki locations were found to significantly support higher cowpea grain yield than the other two locations. The local variety, IT89KD-288, IT1069-6, IT90K-568-1 and IT98K-131-2 constituted the vertex genotypes within the biplot model, indicating that the five genotypes were genetically divergent from each other with respect to the traits assessed. Similarly, the four locations individually occupied the vertices of the biplot polygon indicating that they are inherently different from each other justifying their use for this study. The local variety and IT89KD-288 (an improved photosensitive long duration genotype) gave significantly higher dry and fresh fodder weight and took longer time to bloom and attain maturity. However, the two genotypes performed significantly poorer for grain yield in all the locations suggesting that they are purely fodder type cowpea. Brown seeded cowpea genotypes out yielded the white seeded in all the locations of the study revealing that cowpea with brown seed coat color are better adapted to southeastern Nigeria than white seeded genotypes.
Keywords: Grain cowpea, genotypes, yield component, multi-location, evaluation