Studies on White-Belly Rice Kernel : V. On the occurrence of white belly during the development of rice kernel, with special reference to the moisture content of kernel

Abstract

These studies in series were devoted to clarify the characterstics of white belly rice kernel which had an opaque part at the ventral portion of its endosperm. In this experiment, the stage of initiation of white belly in the developing kernel and the relationship between occurrence of white belly and dehydration of kernel were investigated. The varieties used were Nihonkai, Kinmaze, Norin no. 8, Gohyakumangoku (Sakamai) and Sekaiichi (upland rice) of Japonica and Keikyakusen of Indica type of rice. The following results were obtained. I. Stage of initiation of white belly in fresh kernel differed with variety. In case of varieties which characterized by high occurrence and large size of white belly (external-internal white belly type), the initiation began 15-18 days after flowering when the kernel gained 89-95% of dry weight and 28-29% of moisture. The varieties featured by small white belly (external white belly type), on the other hand, initiated white belly 24-32 days after flowering when the kernel nearly attained its maximum dry weight and the moisture content of kernel decreased to 23-25%. Percentage of white belly increased with the progress of maturation and dehydration. The highest value of white belly was indicated with the attainment of maximum dry weight in case of external-internal white belly type and that of full ripe stage in case of external white belly type. 2. Initiation of white belly in dry kernel occurred earlier than that of fresh kernel. In case of external-internal white belly type, the stage of initiation was 12-15 days after flowering when the kernel had 33-34% of moisture and dry weight index value of 79-83. Whereas, in case of external white belly type, the initiation occurred 19-23 days after flowering when the kernel had 26-29% of moisture and dry weight index value of 88-92. The percentage of white belly increased with the development of kernel and reached at its highest value when the kernel just before attained maximum dry weight in case of external-internal white belly type and when the kernel attained maximum dry weight in case of external white belly type. 3. When the premature fresh kernel were dried artificially, the white belly appeared as the moisture content decreased and the moisture content at which the white belly initiated differed with the kernel age. 4. In fresh kernel, the moisture content of ventral portion was higher than that of dorsal portion, but this moisture state was reversed after the kernel was dried. This phenomenon seemed to indicate that the ventral portion of kernel had less deposition of storage matter and stronger dehydration capacity than the dorsal portion. It was also thought that this phenomenon might be related to the formation of porous tissue of white belly on the ventral portion of kernel. 5. In the premature fresh kernel of Gohyakumangoku a white core variety, the white core occurred with the progress of artificially dehydration in the same way as that of white belly, but the occurrence of white core was associated with slightly lower moisture range than that of white belly. 6. The occurrence of white belly was influenced by the condition of drying. And the dryings which resulted to the rapid dehydration of premature kernel increased the occurrence of white belly.