Phenotypic Stability for Selected Traits of Some Cowpea Lines in Nigerian Agro-ecologies

Eight advanced breeding lines of cowpea [Vigna unguiculata (L.) Walp.] were evaluated in a multi-environment trial for phenotypic stability of grain yield, maturity and grain size. There was highly significant genotype x environment interaction for all traits. Simple correlation coefficient was computed to ascertain the level of relationship between stability parameters and agronomic traits. Line IT93K-452-1 was identified as most stable genotype and can be grown all over the Nigerian cowpea belt. The line IT90K-503-1 was the most unstable genotype in terms of grain yield and was also nonresponsive to the environment. However, it is environment specific. IT93K-452-1 has relatively stable maturity across environments. The result suggests that IT93K-452-1 will mature around the average of 65 days irrespective of the location in Nigeria. Lines IT95K-1455 and IT90K-503-1, whose stability parameter values were high, means that in respect of maturity, they are photo-thermo sensitive. They can mature early or delayed depending on the photo-thermal environment. However, lines such as IT93K-273-2-1, IT93K-129-4, IT93K-452-1 and IT86D-719 are photo-thermo insensitive. Line IT93K-1543 was identified as the most desirable genotype in terms of grain size. This is followed by IT93K-452-1. The line IT90K-503-1 had small but unstable seed size. This work identified IT93K-452-1 and IT93K-273-2-1 as the most stable genotypes for yield and maturity. Grain yield was highly positively correlated with bi and R2 but was negatively correlated with S𝑑²ᵢ. Maturity was negatively highly correlated with bi, Wi, and CVi. Grain size on the other hand is not correlated with any of the parameters.