Response of maize kernel number to shading stress : timing of sensitivity in the reproductive stage and characteristics of genotypes differing in this sensitivity

Abstract

There have been many investigations into the time interval when yield is most susceptible to stress. Knowledge of this interval is important to understanding yield potential, for modeling, irrigation scheduling, and the study of the partitioning of assimilate into grain. The first objective of this experiment was to determine the time near silking when shading stress decreased the number of kernels per ear in maize (Zea mays L.). Once this was defined, the second objective was to look at the relationship between modeled net assimilation rate (NAR) during this interval and final number of filled kernels for maize genotypes having differences in potential number of kernels. In the first segment of this experiment, three commercial maize hybrids were grown on a Houston Black clay (fine montmorillonitic, thermic Udic Pellusterts) under irrigation near Temple, Texas, during 1981, 1982, and 1983. Plants were stressed using horizontal shade panels that reduced the light by 78% for approximately 13-day intervals. The interval when shading decreased the final kernel number was closely associated with early kernel development, beginning soon after silking. The interval length varied from 6 to 29 days. In three of the five cases when kernel number was significantly decreased, the interval was 6 to 7 days. In the second segment of the experiment, three maize inbreds and six maize hybrids were grown under high fertility and irrigation on a Houston Black clay in 1984. Dates of silking, leaf area at silking, final number of kernels, and final dry weight of various plant parts were measured. Five of the six hybrids had a significant relationship between final number of kernels and modeled net assimilation rate. The linear responses for these hybrids were significantly different. Number of spikelets at silking and dry weight of the ear at the beginning of the effective filling period had no significant ([alpha] = 0.05) relationship to fin al number of kernels. Tassel dry weight was greater for hybrids with more kernels per unit of NAR. All six hybrids showed a significant ([alpha] = 0.10) relationship between fin al number of kernels and modeled NAR of leaves above the ear.