Abstract
In order to study the adaptability to high temperature in ripening periods, following experiments were carried out. (1) Thirty varieties of lowland rice were cultivated in early and late season, and the daily process of kernel development, carbohydrate contents in leaves and culms, parcentages of partially-chalky kernels and milk-white kernels, and thickness of bran layer were investigated. In the ripening periods, the max. temperature or min. temp. was 28∼36°C or 21∼261°C in early cultivation, while in late cultivation it was 25∼32°C or 19∼24°C respectively. (2) Three varieties were treated in an air-conditioned room with night temperature of 30°C and 23°C through out the ripening periods (AH, AL) or for 10 days after heading (H, L), and investigations were done as in (1). The results are summarized as follows: 1. High temp. accelerated the kernel development and maturation. The maturation was too fast to be fully filled up by carbohydrate, so that the considerable amount of carbohydrate remained in leaves and culms. This tendency to prematurity caused the occurence of partially-chalky kernels and milk-white kernels and the increase of thickness of bran layer and also of layer of aleurone cells. 2. These facts came out remarkably in some varieties but did not in other varieties, on account of the varietal difference in adaptability to high temperature in ripening periods, for instance, variety Ou-225 was affected scarcely when night temperature was 25∼26°C but fairly affected at 30°C, whereas, variety Fujisaka-5 was affected to greater extent at 25∼26°C and severely at 30°C.
