Variation of the Appearance Quality of Glutinous Rice Grains Among Years and Among Areas, and Its Occurrence Factors in the Coldest Region for Rice Cultivation in Hokkaido, Japan

Appearance quality of glutinous rice grains produced in the six areas of cultivation in the coldest regions for rice cultivation in Hokkaido, Japan was investigated during four years. Among years, the higher the temperature during the stage sensitive to sterile-type cool injury, and the cumulative daily mean temperature during 40 days after heading (grain-filling temperature), the lower the sterility, the heavier the 1000-kernel-weight, the higher the grain yield, higher the percentage of whole grain, the lower the percentages of immature, damaged and colored grains, the lower was the protein content, and the higher was the whiteness of both brown rice and milled rice. On the other hand, the relationship among the 6 areas was not clear. This was because the range of the yearly variation (differences between the two extreme values and coefficients of variation) in the temperatures during the growth stages, the growth characteristics, and the percentages of both whole grain and immature grain were larger than the regional variations. However, the range of the yearly variation in the percentages of damaged grain and colored grain were smaller than the regional variations, and the percentages of damaged grain and colored grain were the lowest in the quadratic regression relationship, at the grain-filling temperature of 843 ℃ and 857 ℃, respectively, among the 6 areas during the 4 years. In addition, the percentage of whole kernels varies between years and regions, and the affected kernels and colored kernels only change between years; the worse these characteristics, the the larger the coefficient of variation among years in the same area or among areas in the same year. Moreover, glutinous grains, called mihaze grains, that are translucent after drying, did not show clear differences in physicochemical characteristics such as contents of both protein and starch, size of starch granules, iodine absorption spectrum of prepared starch and lightness of rice-cake dough as compared with the opaque grains called haze, and did not show large differences in physical property of rice-cake dough. Therefore, contamination of mihaze grains is considered to have little effect on the processing quality of rice-cake dough. Xenia seeds of glutinous rice plants occurred by outcrossing with pollen of a non-glutinous variety, and were found more in rice plants with high sterility than those with low sterility. The longer the isolation distance from non-glutinous variety to glutinous rice plant; the lower was the Xenia seed rate. However, Xenia seeds were found even at an isolation distance of 600 m. Therefore, in Hokkaido, to avoid quality deterioration, glutinous rice varieties should be cultivated in a district distant apart from paddy fields of non-glutinous rice varieties.