Genetic analysis of grain yield and other traits of extra-early yellow maize inbreds and hybrid performance under contrasting environments

Maize (Zea mays L.) is a major staple crop in West and Central Africa (WCA) but production is constrained by Striga hermonthica parasitism and recurrent drought in the savannas where maize yield potential is highest. Two studies were conducted for 2 years at 5 locations in Nigeria. The objective was to determine the combining ability of seven extra-early yellow-endosperm inbreds, place them into heterotic groups, identify the best testers and superior single-cross hybrids under drought, Striga infestation, optimal conditions and across environments. General combining ability (GCA) and specific combining ability (SCA) mean squares were significant for grain yield and most other traits across test environments. Mean squares for GCA were larger than those of SCA in all environments, indicating that additive gene action was more important in the inheritance of traits. Three testers (TZEEI 79, TZEEI 76 and TZEEI 63) and opposing heterotic groups (TZEEI 95, TZEEI 78, TZEEI 79), (TZEEI76, TZEEI 82) and (TZEEI 63, TZEEI 58) were identified across environments. TZEEI 79 had the highest positive GCA effects for grain yield across environments. Furthermore, TZEEI 95 × TZEEI 79 was identified as the potential single-cross tester for the development of three-way and double-cross hybrids. Results of repeatability analysis showed that the managed drought test site, IKDT, was the most repeatable even though it was not very discriminating. In contrast, ZAWW had high representativeness, discriminating ability and repeatability, indicating that it was the ideal test location. The best extra-early hybrid TZEEI 79 × TZEEI 63 under drought stress and TZEEI 82 × TZEEI 79 under Striga infestation were comparable in yield to the best open-pollinated early check. GGE biplot analysis revealed TZEEI 79 × TZEEI 76 as the highest yielding and most stable hybrid across environments. The available extra-early maize inbred lines are not only drought escaping but also possess genes for drought tolerance.

► Three testers (TZEEI 79, TZEEI 76 and TZEEI 63) were identified across environments.
► Three opposing heterotic groups were identified across research environments.
► Additive gene action is important in the inheritance of traits across environments.
► TZEEI 95 × TZEEI 79 was identified as the potential single-cross tester.
► TZEEI 79 × TZEEI 76 was the highest yielding and stable hybrid across environments.