Abstract
Factors of occurrence of chalky grains including milky white rice grains, white-based rice grains and white-back grains in rice, were studied. From the analysis of the relationship with the percentage of first class grade rice produced in Tochigi prefecture, the weather conditions and the growth of rice, the factors causing occurrence of chalky grains in rice were found to be the saturation deficit and ventilation from 6 to 25 days after heading, the temperature for 20 days before and after heading, the daylight hours for 30 days before heading, and the number of spikelets per panicle. When kept under ventilation for 6-10 days after heading, white-based rice grains and white-back rice grains occurred in every position on the panicle. On the other hand, when kept under ventilation for 21-25 days after heading, milky white rice grains occurred on the primary rachis-branch at top and medium positions. The rate of chalky grains was high on inferior spikelets. The rate of chalky grains in rice could be estimated from the mean temperature from 0 to 20 days after heading and [(100-minimum humidity)×maximum wind velocity] from 6 to 25 days after heading. The occurrence of chalky grains varied with the cultivar.
