Crop-Scientific Studies on White-Core Kernels of Rice : Part 7 The relationship between the ripening grade of a hull rice and the occurrence of a white-core kernel of rice

摘要

An investigation was carried out to clarify the relation between the occurrence of a white-core kernel and the ripening grade of a hull rice, using some varieties of rice with bigger grains, e.g. Hyogo-omachi, Yamadanishiki and others. The ripening grade was divided into sixteen ranks, according to specific gravity of a hull rice, ranging from 0.09 to 1.20 with an interval of 0.02. Moreover, the hull rice belonged to the respective rank of specific gravity was radiographed by the soft X-ray apparatus (SOFTEX type-EM) for the purpose of detecting a vacant space in a hull rice. The results obtained are summarized as follows: (1) The occurrence of a white-core kernel was proportionally increased with specific gravity of a hull rice and the white-core portion was born for the first time in a hull of which specific gravity was nearly from 1.08 to 1.12, being true for all the varieties tested. The frequency of occurrence of type A, one of the five types in white-core kernels, as reported previously, showed the highest positive correlation with specific gravity of a hull rice. (2) The radiographs of a hull rice revealed that a rice grain grew up with an increase of specific gravity of a hull rice, consequently diminishing a vacant space in a hull rice. It was also noticed that the dimension of a vacant space and the size of a grain, in a hull, in which a white-core kernel had to be produced were greater than those in a hull containing a non-white-core kernel. (3) On the basis of this investigation, it may be concluded that the white-core portion in a rice grain are apt to be produced when a hull rice is growing under such a favorable condition for ripening as both a hull and a grain in it are able to grow up to the size peculier to the variety with bigger rice grains.