Combining Ability and Heterotic Patterns of Early-Maturing Provitamin a Inbreds Under Contrasting Environments.

Vitamin A deficiency is a major health problem in sub-Saharan Africa (SSA). The maize plant can accumulate significant quantity of Provitamin A (PVA) in the endosperm and has significant genetic variation for the PVA trait. Therefore, increasing PVA level in maize through breeding is a feasible approach for alleviating PVA deficiency. Apart from PVA problem, maize production in SSA is constrained by Striga hermonthica parasitism, drought and low soil nitrogen (low-N). Therefore, there is need to develop and commercialize multi-stress tolerant PVA maize in the effort to fight malnutrition in SSA. The objectives of this study were to determine the combining ability of 20 early-maturing PVA maize inbreds under contrasting environments, classify the inbreds into heterotic groups, identify testers and examine performance of inbreds in hybrid combinations. One hundred and ninety diallel crosses involving the 20 inbreds plus six yellow-endosperm hybrid checks were evaluated under drought, Striga-infested, low-N and optimal environments in Nigeria, 2016. Significant mean squares were obtained for general combining ability (GCA) and specific combining ability (SCA) effects of most traits across environments. There was predominance of GCA effects for most traits, suggesting that additive gene action was more important than the non-additive. Inbreds were classified into three heterotic groups each based on GCA of multiple traits (HGCAMT) and heterotic groups’ SCA and GCA of grain yield (HSGCA) methods. Only TZEI 129 was identified as tester across environments. This tester displayed significant and positive GCA for grain yield and ears per plant as well as significant and negative GCA for Striga damage and could be invaluable source of beneficial alleles for development of superior PVA populations and hybrids for the tropics. The AMMI biplot identified PVA hybrids TZEIOR 2 x TZEIOR 157, and TZEIOR 4 x TZEIOR 65 as outstanding in yield and stability across environments and should be commercialized in SSA.