Abstract
Two rice varieties (Hattan-Jugo and Yamada-Nishiki) planted in pots were treated during night time with room temperature of 30, 23 and 13°C for 7 days around the seed-developing time and for 22 days after heading. Fruiting, qualities of kernels and types of white-core kernels were investigated on the samples. Dorsal and ventral radii of kernels were also measured on the crossections. Results and discussion are summarized as follows: 1) High night temperature accelerated the kernel develapment and maturation. Low night temp. worsened the fruiting and qualities of the kernels and retarded the kernel growth. 2) Percentages of white-core kernel were high in the high temp. plots and low in the low temp. plots. 3) Many of white-core kernels from low temp. plots were milky-white-like and somewhat white-belly-like, and were eye-shaped when observed on the cross-sections. 4) High temp. lenghened considerably the ventral radii of kernels and shortened to some extent the dorsal radii of kernels while low temp. shortened the ventral radii, especially in the early stages of seed growth. 5) Promotion of early growth of kernel as indicated by well-developed ventral side in the case of high temp. treatment may lead to the well-developed thin-cell tissues along the dorso-ventral diameter of the kernel. These tissues seemed to be low in ability of storing starch and apt to form white-core parts in themselves. Retardation of early growth of kernel as incured by low temp. seemed to obstruct the development of ventral side and thin-cell tissues, and censequently occurrence of white-core.
