Genotype by environment interaction results in significant differences in the performance of cultivars when tested in diverse environments. Nine improved cowpea (Vigna unguiculata (L.) Walp) cultivars obtained from International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria and a local check were evaluated for growth, reproductive and grain yield components in a non-traditional cowpea growing region of south eastern Nigeria with the aim of identifying high yielding genotypes and optimum planting date. The study was conducted in two locations namely Mgbakwu (06°17ʹN, 07°04ʹE; 83 masl) and Ishiagu (05°58ʹN, 07°34ʹE; 197 masl) across two years and two seasons in each year. A split-plot design was used with three replications. The results indicated that early planting date gave significantly higher yield and yield components than late planting date in both years and locations. IT 98K-131-2 produced mean grain yield of 1220 kg ha-1 in early planting date and 732 kg ha-1 in late season planting in Ishiagu, while in Mgbakwu, it produced 921 and 326 kg ha-1 in early and late planting dates, respectively. IT 97K-556-4 on the other hand produced mean grain yield of 1154 and 424 kg ha-1 in early and late planting dates, respectively in Ishiagu; while in Mgbakwu, the mean grain yield were 1594 and 251 kg ha-1 for early and late planting dates, respectively. IT 98K-131-2 exhibited the highest mean grain yield attributes in all the environments, indicating broad adaptation; while IT 97K-556-4 was the next highest grain yielder with specific adaptation to early season in Mgbakwu. The two cultivars are therefore recommended to farmers for multiplication and general cultivation in south eastern Nigeria. 

 

Key words: Cowpea, growth and yield components, planting date.