2020 Volume 89 Issue 2 Pages 102-109
NARO recently developed rice (Oryza sativa L.) cultivars, “Akidawara”, “Yamadawara” and “Toyomeki” which had high yield and high eating quality. The filled brown rice yield of these cultivars was approximately 800 g m–2, while that of a popular cultivar “Koshihikari” was 500 g m–2. The higher yield was attributed to the larger number of total spikelets m–2. To determine the suitable harvesting time of these cultivars to optimize grain yield and quality, we examined the correlation of accumulated temperature after heading with the perfect grain ratio, water content of hulled grain, percentages of filled spikelets and hulled grain yellowing rate. The accumulated temperature after heading, where the percentage of perfect grain was more than or equal to 70% and water content of hulled grain was less than or equal to 25%, was 1115–1393, 1247–1441 and 1171–1480ºC・day, in “Akidawara”, “Yamadawara” and “Toyomeki”, respectively. This was when the percentage of filled spikelets reached almost the maximum level and the hulled grain yellowing rate was 88–95, 87–94 and 82–92%, in “Akidawara”, “Yamadawara” and “Toyomeki”, respectively. Therefore, these ranges of accumulated temperatures were concluded to be the suitable harvesting time.
