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tion in an elite lowland tropical maize population 'Tuxpeñ o Crema I' (Johnson et al., 1986(Johnson et al., ) in 1975 Drought is common in tropical environments, and selection for conditions of managed drought stress. This population, drought tolerance is one way of reducing the impacts of water deficit on crop yield. The primary objective of this study was to evaluate later renamed 'Tuxpeñ o Sequia', underwent eight cycles biomass, grain yield, and harvest index of maize (Zea mays L.) popula-G.O. Edmeades, Pioneer Hi-Bred International, Inc., 7431 Kaumualii

A shortened anthesis‐to‐silking interval (ASI) in maize (Zea mays L.) is associated with tolerance of stresses which occur around flowering. It is not known if this reflects differences in tassel and ear initiation dates, or in rates of development and growth. We examined these characteristics in selection cycles 0, 2, 4, 6, and 8 (designated Cx, where the subscript indicates the cycle number) of the lowland tropical maize population ‘Tuxpeño Sequía’, which was selected recurrently for drought tolerance and whose selection cycles differ for ASL Plants were grown at high plant density and under mild and severe drought stresses that occurred at flowering. Silking was delayed significantly, especially in C0 and C2 under severe drought. Stress treatments did not affect days to 50% tassel initiation, ear initiation, or anthesis. The interval between 50% tassel and ear initiation, the rate of spikelet initiation, and crop growth rate near flowering were unaffected by selection. Per cycle changes were −0.21 d in duration of ear spikelet initiation and −16.9 for spikelet number per ear at 50% anthesis. Selection changed relative growth rates at 50% anthesis by 0.005 d−1 cycle−1 for ears, 0.007 d−1 cycle−1 for spikelets and −0.009 d−1 cycle−1 for tassels. These changes were unaffected by stress level. Eight cycles of selection increased the mean ear and spikelet weights at 50% anthesis by 127 and 173%. The ASI increased rapidly when mean spikelet biomass at 50% anthesis was less than 0.8 rag. Results indicate that a decreased ASI arising from selection in this population is due largely to an increased rate of biomass accumulation per spikelet, and development of fewer spikelets per ear.

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