DEVELOPMENT AND GROWTH OF TROPICAL MAIZE AT 2 ELEVATIONS IN HAWAII

Development and growth response of maize (Zea mays L.) to an increase in temperature and daylength has been studied in temperature regions, but little is known of the effects of daylength on leaf number, leaf area development, and grain yield in tropical environments. A temperature-by-daylength experiment was conducted in the field on the Island of Maui, Hawaii (USA) at 282 and 640 m elevations during summer 1988 to examine the effects of daylength and temperature on leaf number, leaf area index (LAI), and grain yield of Pioneer hybrid X304C. Under high nutrient fertility and adequate water supply, plants were grown at natural daylength (12-13.5 h, control), control + 0.5-h, 14-, 17-, and 20-h daylengths. These daylengths were artificially produced by extending the natural daylength with 500-W lamps. For a 97-d period, mean maximum air temperatures were 26.8 and 27.8-degrees-C while minimum air temperatures for the same period were 20.1 and 16.4-degrees-C at the 282 and 640 m elevations, respectively. Longer days reduced mature leaf appearance rate and delayed tassel initiation and tasseling. Leaf tip appearance rate was unaffected by daylength but leaves took more thermal time for full expansion. Leaf area index in the 17- and 20-h daylengths was 7.0 at 77 d after planting, which was 1.8 times the LAI in the control and 14-h daylengths. Physiological maturity in the 17-h daylength was delayed by 33.5 and 38.5 d at 282 and 640 m, respectively. Maturity in the 20-h daylength was delayed by 41.0 and 48.5 d at 282 and 640 m, respectively. Grain yields and harvest indices at both elevations decreased significantly with increasing daylength. Overall, warm temperatures at 282 m enhanced the adverse effects of daylength on grain yield.