Corn Growth Response to Temperature and Photoperiod. III. Leaf Number1

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Abstract
The number of leaves formed on a determinate plant species such as corn (Zea mays L.) is dependent on the time between sowing and tassel initiation and on the rate of leaf production at the apical meristem. Both of these processes, and consequently leaf number, are influenced by environmental variables such as temperature and photoperiod. In a controlled‐environment study of two corn hybrids, grown over a wide range of temperature regimes from 16/6 to 38/33°C day/night, a nonlinear leaf number/temperature response was observed. Leaf number was lowest near 18/18° C and highest in the 16/6 and in the 38/33°C conditions. Because of this nonlinearity, leaf numbers observed under differential day/night temperature regimes were sometimes quite different from those observed under constant day/night temperatures but with identical mean temperatures. A leaf number/temperature response function was estimated for each of the hybrids which could be used to predict leaf number for various temperature regimes with 12‐h photoperiods. The response function was found to be in agreement with results in the literature. Differences in leaf number between the two cultivars were consistent with their maturity ranking. Leaf number increased as photoperiod increased; an average increase of 0.71 leaves per additional hour of photoperiod was found. This increase obtained under high light conditions is greater than that recorded previously for other temperate cultivars grown under long day conditions provided by low intensity day‐length extensions from incandescent lighting. Photoperiod sensitivity was not altered by temperature. The number of unexpanded leaves present at tassel initiation was almost constant under different temperature treatments despite changes in total leaf number. In contrast, this number increased when photoperiod was increased. The main ear node position altered with changes in total leaf number but was almost constant relative to the number of mature leaves present at tassel initiation under all temperature and photoperiod treatments.