Abstract
The effect of the amount of nitrogen application on the occurrence of white-back kernels was examined in rice grown in warm areas. White-back kernels occurred when the average temperature during ripening 20days after heading was 27°C or higher, especially at 28°C or higher temperature. At 28°C or lower temperature, white-back kernels tended to decrease with the increase in amount of nitrogen application. A negative correlation was found between the protein content (nitrogen content) of brown rice and the occurrence of white-back kernels. The preferred protein content of brown rice was estimated to be 6.0-7.0%considering the palatability because the occurrence rate of white-back kernels increased when protein content of brown rice was less than 6.0%, whereas palatability dropped when it was greater than 7.0%. At temperatures higher than 28°C, white-back kernels occurred frequently in cultivars such as Hatsuboshi and Hinohikari, whose ripening are "sensitive" to high temperatures, showing little suppressive effect of the increase in the nitrogen contents of brown rice, on the occurrence of white-back kernels. Thus, it is difficult to decrease the occurrence of white-back kernels at temperatures higher than 28°C merely by increasing the amount of nitrogen application in these cultivars. Thus, introduction of cultivars resistant to high temperatures during ripening is also necessary to reduce white-back kernels.
