Effects of the amount of insolation and humidity during the ripening period on the grain quality of brown rice in warm regions of Japan

Abstract

The effects of the amount of insolation and humidity during the ripening period on the occurrence of white-back kernels in paddy rice, were investigation in a paddy field with shading treatment and in a climatron under a high-temperature condition while varying the solar radiation and humidity. The incidence of white-back kernels was high under the high-temperature condition, although there were fewer white-back kernels and a tendency of more milky white kernels in the shading treatment group. In the climatron, there were more white-back kernels at a high humidity was high or large amount of insolation. The panicle surface temperature under the same high-temperature condition was higher when humidity was higher or the amount of insolation was higher, revealing a similar tendency to that of the incidence rate of white-back kernels. These results indicate that the incidence rate of white-back kernels varied with the amount of insolation and humidity, even under the same high-temperature condition. These results suggest that white-back kernels were significantly influenced by the surface temperature of the panicle, which was closely related to the amount of insolation and humidity, and also by the air temperature. The incidence of white-back kernels was affected significantly by the high-temperature condition during the ripening period. In contrast, the incidence of milky white kernels was influenced more by the amount of insolation rather than by the high-temperature condition; their occurrence was promoted by the increase in the number of rough rice grains.