Abstract
Variations of sterility induced by cool-irrigation tolerance (18.5°C, 30cm) due to years and period of cool-irrigation were examined in Iwate Prefecture, Japan, using three rice cultivars for 4 years. The cool-irrigation tolerance test started at 37-34 days before heading (“standard”) and at a week earlier (“long-period”). Spikelet sterility was significantly lower in the tolerant cultivar ‘Hitomebore’ than in other cultivars, and was higher in 2005 and 2006 than in 2007 and 2009. A long irrigation treatment significantly increased spikelet sterility over cultivars and years. The spikelet sterility was in the range of 29−61％ in ‘Hitomebore’, 77−93％ in ‘Akihomare’ and 63−95％ in ‘Toyonishiki’. The difference in sterility in each treatment was analyzed by the simple regression to air temperature, water temperature and solar radiation averaged for 14 successive days during a period from 49 days before heading to 7 days after heading for each cultivar. The difference in sterility of each cultivar was explained by water temperature during 42 to 28 days before heading stage. The long treatment covering the 42 to 28 days before heading stage could reduce the yearly variation of spikelet sterility by 5 points (standard deviation) compared with standard treatment although it delayed the heading date by a few days.
