2022 Volume 91 Issue 3 Pages 230-238
The percentage of first grade Koshihikari rice （a paddy rice variety） produced in Niigata Prefecture was over 70％ from 2013 to 2018. However, the ratio in 2019 （25％） was the second lowest ever. In 2019, the temperature from late-July to mid-August was 1.4-4.0°C higher than usual, reaching a record high temperature due to the foehn winds that occurred from August 14 to 15. The reason for the downgrading was mostly milky white grains. Despite this observation, it was speculated that excess spikelet number was not the main factor. The pattern and proportion of cross-sectional chalkiness in brown rice grains was investigated in Koshihikari samples with different heading times. A combination of chalkiness in center, dorsal and ventral sides was confirmed in samples exposed to the foehn winds 11 to 17 days after heading time. In these samples, the ratio of dorsal chalkiness was also increased, and the ratio of perfect grains was low. Peak heading time for Koshihikari in Niigata Prefecture was August 3, suggesting that the quality deteriorated due to exposure to the foehn winds in the first half of ripening, when the rice is highly sensitive to the increase in temperatures in most areas.
