Extraordinary hot summer in Hokkaido decrease rice yield and satisfy growing of cultivar in Tohoku region “Hitomebore”

Abstract

The summer temperature in Hokkaido in 2010 was the hottest on meteorological record and caused the crop index of rice (Oryza sativa L.) to drop below average. The mean temperature was 2.2°C higher than normal (based on the period 1981-2010) and was coincident with climate change predictions for the end of the 21st century. To investigate possible measures against the hot conditions projected in Hokkaido and the resulting reductions in yield, we tested Hitomebore, a cultivar from the Tohoku region of Japan. Although local cultivars had been used in accordance with conventional procedures, 2010 was the first year in which Hokkaido's rice yield was decreased by factors other than cold injury or strong winds. The extremely high temperature in June probably shortened the basic vegetative growth period, thus reducing the number of tillers and number of grains. However, Hitomebore grown at our experimental paddy field in Sapporo under the hot conditions of 2010 reached the heading stage during a period when it was safe from cold-induced injury, and it ripened fully to give a yield of 6300 kg/ha. Introduction of new cultivars with properties similar to those of Hitomebore will be one way of adapting to the expected climate change.