Formation of Heterotic Groups and Understanding Genetic Effects in a Provitamin A Biofortified Maize Breeding Program

Abstract

ABSTRACTDeveloping biofortified maize (Zea mays L.) cultivars is a viable approach to combating the widespread problem of vitamin A deficiency among people for whom maize is a staple food. To enhance CIMMYT's provitamin A maize breeding efforts, this study: (i) evaluated whether separation of experimental maize lines into groups based on maximizing their molecular‐marker‐based genetic distances (GD) resulted in heterosis for among‐group crosses, (ii) assessed genetic effects (general and specific combining ability, GCA and SCA) for grain yield and provitamin A concentrations in hybrids among 21 inbred lines representing the three proposed groups, and (iii) assessed the association between grain yield and provitamin A concentrations. The lines were crossed following a partial diallel design resulting in 156 hybrids that were evaluated at four environments with two replications of one‐row plots. The first plant in each plot was self‐pollinated to produce grain for provitamin A analysis. Significant but small yield advantage of among‐ versus within‐group crosses (0.47 Mg ha−1, P < 0.05) suggested that the groups identified by maximizing GD could be a practical starting point for further breeding work to develop useful heterotic groups. Furthermore, the GD‐proposed heterotic groups were improved by later revising some line assignments to groups using estimates of SCA effects. General combining ability effects were significant (P < 0.01) for all traits, whereas SCA effects were weak (P < 0.05) or not significant for provitamin A carotenoid concentrations, indicating that these were controlled primarily by additive gene action. Grain yield was not significantly correlated with provitamin A concentration, indicating that both traits could be improved simultaneously.