Genetic Analysis of Inbred and Hybrid Grain Yield under Stress and Nonstress Environments in Tropical Maize
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Drought and low soil N cause significant yield reductions in maize. (Zea mays L.) grown in the tropics. Understanding the genetic basis of hybrid performance under these stresses is crucial to designing appropriate breeding strategies. This study evaluates under optimal, drought and low N stress conditions (i),the performance, combining abilities and stability of a group of tropical white inbred lines; (ii) the genetic control and modes of gene action for grain yield; and (iii) the relationship between line per se and hybrid performance. Seventeen lowland white-grained tropical maize inbred lines, were used in a diallel study. Lines and their hybrids were evaluated separately in trials under drought stress, low N, and optimal conditions in a total of 12 environments. The differences in grain yield between hybrids and inbreds (i.e., heterosis) increased with the intensity of drought stress. Significant interactions were observed for combining abilities under low and high N. The type of gene action appeared to be different under drought than under low N, with additive effects more important under drought and dominance effects more important under low N. The importance of additive effects increased-with intensity of drought stress. This suggests the need for drought tolerance in both parental lines to achieve acceptable hybrid performance under severe drought. Inbreds derived from the population 'La Posta Sequia' exhibited the highest GCA effects, stability coefficients, and frequency of dominant alleles for grain yield. Good performance across stress levels can be achieved in tropical maize hybrids.
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