Abstract
The properties of rice kernel starches of Norin-17 (Japonica type) and IR-8 (Indica type) ripened from fertilization to maturity under different air temperatures combined with photoperiod, light intensity and air-humidity were compared by testing their alkali decomposition value and X-ray diffraction pattern. The alkali decomposition values of Norin-17 were always lower than those of IR-8, indicating that the former is more resistant to alkali. In the regime of this experiment, higher air-temperatures especially during daytime decreased the value. At higher temperatures longday condition seemed to decrease it. Light intensity and air-humidity had little effect on the value. Under the differential conditions tested, X-ray diffraction patterns of Norin-17 varied from type II to type III, while those of IR-8 varied from type I to III with a wider range. Norin-17 starches ripened under the lowest or the highest temperature showed type II, in cotrast, IR-8, starches was type I when matured at lower temperatures or very cool night temperatures, but showed type III when ripened at the highest temperature. At such high temperatres as 35-25 or 30-20°C, type II and type I under shortday condition changed to type III and II, respectively, under longday condition. The patterns were little affected by air-humidity, but were influenced by light intensity; type I and type II under weak light condition changed to type II and III, respective1y, under strong light. In general, alkali decomposition value and X-ray diffraction patterns varied parallel, but sometimes with discrepancy, the cause of which is not clear.
