Efficiency of high-nitrogen selection environments for improving maize for low-nitrogen target environments
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Most maize (Zea mays L.) in the tropics is grown under low-nitrogen (N) conditions, raising the need to assess efficient breeding strategies for such conditions. This study assesses the value of low-N vs. high-N selection environments for improving lowland tropical maize for low-N target environments. Fourteen replicated trials grown under low (no N applied) and high (200 kg N ha(-1) applied) N at CIMMYT, Mexico, between 1986 and 1995 were analyzed for broad-sense heritability of grain yield, genetic correlation between grain yields under low and high N, and predicted response of grain yield under low N to selection under either low or high N, Broad-sense heritabilities for grain yield under low N were on average 29% smaller than under high N because of lower genotypic variances under low N, Error variances were similar at low and high N, Genetic correlations between grain yields under low and high N were generally positive, They decreased with increasing relative yield reduction under low N, indicating that specific adaptation to either low or high N became more important the more low-N and high-N experiments differed in grain yield. Selection under high N for performance under low N was predicted significantly less efficient than selection under low N when relative yield reduction due to N stress exceeded 43%, Maize breeding programs targeting low-N environments in the tropics should include low-N selection environments to maximize selection gains.
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