MAIZE LEAF NUMBER SENSITIVITY IN RELATION TO PHOTOPERIOD IN MULTILOCATION FIELD TRIALS

The photoperiodic response of maize (Zea mays L.) determines the total number of leaves (LN). Knowledge of this is important for modeling phenology and for describing cultivar adaptation. The objective of this research was to evaluate artificial extension of photoperiod for field-grown maize as a method of quantifying photoperiodic sensitivity. The LN response was quantified using data from six diverse maize cultivars grown at two field locations where natural photoperiods were artificially extended by 1.3 h to 7.3 h. These responses were then compared with LN observed in a field experiment of the same cultivars grown at 11 diverse latitudes. The relative ranking of photoperiod sensitivity among cultivars was similar for the two groups of experiments, although observed sensitivity was occasionally greater in artificial light experiments than in multilocation experiments. Photoperiod sensitivity was greater for the tropical than for the temperate cultivars, with mean sensitivities of 1.91 and 0.49 leaves h-1, respectively. The LN in tropical cultivars was reduced by 0.5 to 2.0 leaves plant-1 for every min d-1 increase in rate of change of photoperiod during the photoperiod-sensitive stage. Artificial extension of daylength by lights mounted in the field appears to be an effective and efficient means of screening maize cultivars for photoperiodic sensitivity.