Generation mean analysis of the key earliness related traits in cowpea (Vigna unguiculata (L.) Walp)

Abstract

The nature of gene action controlling agronomic traits enables plant breeders to execute a successful crop improvement programme. To elucidate the type of gene action governing the key earliness related traits in cowpea, seven populations of the six basic generations, viz; P1, P2, F1, F2, BC1 and BC2 were developed by crossing three extra-early and three early-to-medium maturing parental lines. Each of the populations were sowed in Randomised Complete Block Design, in the experimental field of Council for Scientific and Industrial Research (CSIR)-Savana Agricultural Research Institute Manga, Ghana. Observations were made on days to first flower appearance (DFFA) and days to 95% pod maturity (DNPM). The results indicated that the epistatic gene interaction for DFFA in most of the crosses was duplicate epistasis between dominant decreasers. For DNPM, duplicate epistasis between dominant increasers was found. Only Kirkhouse-Benga × CB27 revealed complementary epistasis between dominant decreasers for both traits. Among the significant epistasis terms re-estimated using perfect fit procedure, the χ2 values were not applicable in any of the crosses, indicating the inadequacy of the six-parameter model of digenic epistasis. Therefore, trigenic or other high-order epistasis could be responsible for the inheritance of the traits evaluated. This implies that improvement of earliness in cowpea could be achieved through hybridization method, followed by selection of promising recombinants in later generation, for crosses governed by duplicate epistasis. Complementary epistasis detected for one of the crosses is desirable and would be beneficial in the development of early duration varieties, where selection could be done at early generation. The preponderance of partial-dominance, over-dominance of earliness over late maturity, and significant negative heterosis and heterobeltiosis observed for DFFA and DNPM indicated that the developed of short duration cowpea cultivars would be efficient. The genetics of the three most popular extra-early maturing cowpea genotypes reported in this study could be exploited by breeders to develop extra-early duration varieties.