Genomic prediction is expected to considerably increase genetic gains by increasing selection intensity and accelerating the breeding cycle. In this study, marker effects estimated in 255 diverse maize (Zea mays L.) hybrids were used to predict grain yield, anthesis date, and anthesis-silking interval within the diversity panel and testcross progenies of 30 F2-derived lines from each of five populations. Although up to 25% of the genetic variance could be explained by cross validation within the diversity panel, the prediction of testcross performance of F2-derived lines using marker effects estimated in the diversity panel was on average zero. Hybrids in the diversity panel could be grouped into eight breeding populations differing in mean performance. When performance was predicted separately for each breeding population on the basis of marker effects estimated in the other populations, predictive ability was low (i.e., 0.12 for grain yield). These results suggest that prediction resulted mostly from differences in mean performance of the breeding populations and less from the relationship between the training and validation sets or linkage disequilibrium with causal variants underlying the predicted traits. Potential uses for genomic prediction in maize hybrid breeding are discussed emphasizing the need of (1) a clear definition of the breeding scenario in which genomic prediction should be applied (i.e., prediction among or within populations), (2) a detailed analysis of the population structure before performing cross validation, and (3) larger training sets with strong genetic relationship to the validation set.

Developing 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.

Vivek Maize Hybrid 9-a popular single-cross hybrid developed by crossing CM 212 and CM 145 was released for commercial cultivation in India. The parental lines, being deficient in lysine and tryptophan, were selected for introgression of opaque-2 allele using CML 180 and CML 170 as donor lines through marker-assisted backcross breeding. The opaque-2 homozygous recessive genotypes with >90% recovery of the recurrent parent genome were selected in BC 2 F 2, and the seeds with <25% opaqueness in BC 2 F 3 were forwarded for seed multiplication.Vivek Quality Protein Maize (QPM) 9, the improved QPM hybrid, showed 41% increase in tryptophan and 30% increase in lysine over the original hybrid. The grain yield of the improved hybrid was on par with the original hybrid. The newly improved QPM maize hybrid released in 2008 will help in reducing the protein malnutrition because its biological value is superior over the normal maize hybrids. This short duration QPM maize hybrid has been adopted in several hill states of North Western and North Eastern Himalayan regions.

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