The importance of the anthesis-silking interval in breeding for drought tolerance in tropical maize
1997
Bolanos, J.A. | Edmeades, G.O.
Selection for improved performance under drought based on grain yield alone has often been considered inefficient, but the use of secondary traits of adaptive value whose genetic variability increases under drought can increase selection efficiency. In the collars of recurrent selection for drought tolerance in six tropical maize (Zea mays L.) populations, a total of 3509 inbred progenies (S1 to S3 level) were evaluated in 50 separate yield trials under two or three water regimes during the dry winter seasons of 1986-90 at Tlaltizapan, Mexico. In over 90 Per cent of the trials, ears plant-1, kernels plant-1, weight kernel-1, anthesis-silking interval (ASI), tassel branch number and visual scores for leaf angle, leaf rolling and leaf senescence were determined. Low scores indicated erect, unrolled or green leaves. Canopy temperature, leaf chlorophyll concentration and stem-leaf-extension rate were measured in 20-50 Per cent of the trials. Across all trials, linear phenotypic correlations (P0.01) between grain yield under drought and these traits, in the order listed, were 0.77, 0.90, 0.46, -0.53, -0.16, 0.06NS, -0.18, -0.11, -0.27, 0.17 and 0.10. Genetic correlations were generally similar in size and sign. None of the physiological or morphological traits indicative of improved water status correlated with grain yield under drought, although some had relatively high heritabilities. Genetic variances for grain yield, kernels ear 2, kernels plant-1 and weight kernel-1 decreased with increasing drought, but those for ASI and ears plant-1 increased. Broad-sense heritability for grain yield averaged around 0.6, but fell to values near 0.4 at very low grain yield levels. Genetic correlations between grain yield and ASI or ears plant-1 were weak under well-watered conditions, but approached -0.6 and 0.9, respectively, under severe moisture stress.
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