Genotype W environment interaction effects on some physiological yield determinants in cowpea (Vigna unguiculata (L.) Walp)

A simple crop physiological model was employed to study the yield basis and environmental effects on 31cowpea genotypes of early, medium and late maturities. The tests were carried out at four sites in northern Ghana between 1992 and 1994. Genotypic variations observed for pod yields (Y), reproductive duration (RD), crop growth rates (CGR) and partitioning coefficients (p) were wide. Pod yields averaged 2032, 2170 and 1983 kg ha-1 for the early, medium and the late lines, respectively. The interaction effects of years with genotypes were quite substantial for pod yield and all the other physiological parameters. Partitioning coefficient was more stable than pod yields in the medium and late lines as shown by the non-significant interactions of genotype W location effects. Regression of pod yields and partitioning coefficients with their respective environmental means also showed the latter to be more stable. Plant breeders may, therefore, put selection pressure on p when developing cowpea varieties for the Guinea and Sudan savanna agro-ecological zones, because of its relative stability compared with pod or grain yields. Pod yields correlated with p in all the maturity groups. CGR correlated better with Y for medium and late lines than the early genotypes. This indicates good possibilities for identifying lines which canproduce both haulms for livestocks and pods for human consumption in the medium and late lines. (Ghana Journal of Agricultural Science, 1997, 30(1): 15-22