Varietal Differences in Photoperiodic and Thermal Responses of Wheat

The need for early maturing cultivars is one of the problems Lacing wheat breeders in southwestern Japan. From this point of view, several experiments were conducted to get information on the photoperiodic and thermal responses of wheat cultivars in southwestern Japan. To find the effective natural day length of wheat, an experiment was performed changing light intensity of the frrst and the last 4 hours of a 16-hour photoperiod. The experiment showed that the minimum effective light intensity in the first 4 hours is 10lux and in the Comparing these results with the intensity of the last 4 hours is 20 lux (Figs 3 and 4). morning light and evening twilight, the effective day length in Fukuyama (34° 30' N) was assumed to be the astronomical day length +49 minutes. Considering the fact that the length of twilight is inversely proportional to the peripheral velocity of the earth's surface at a given place, the effective day length and the mean temperature for wheat at heading time and one month and two months before heading time were estimated for all parts of Japan as shown in Fig. 5.