Field survey on rice spikelet sterility in an extremely hot summer of 2018 in Japan

Abstract

In rice (Oryza sativa L.), heat-induced spikelet sterility (HISS) has long been recognized a major threat in the production, and currently the potential risk of yield reduction is likely to be increasing under global warming. However, there have been few studies on HISS conducted under field conditions. In recent years in Japan, extremely high temperatures have frequently recorded in the daytime during the summer. In 2018, heat wave lasted from mid-July to late August, which overlapped the typical rice heading period from eastern to western Honshu and raised a concern about HISS during flowering. To examine this possibility, we surveyed rice sterility in eight prefectures in the Kanto, Tokai, and Kinki regions. During surveys in 2018 and 2019, we collected field data on the sterility of ‘Koshihikari’, the most popular rice variety in Japan, and the sterility ranged from 3.7 to 15.4% in paddy fields. The sterility tended to be higher in the paddy fields where heading occurred during the heat wave. We modeled the sterility rate using the heat dose based on daytime mean panicle temperature, with a threshold for HISS at 33°C. The model estimates based on meteorological data showed that HISS can be induced even under current climatic conditions, depending on the timing of heading. Considering the projected global warming, this study raises an issue that rice plants would face a risk of HISS under the temperate climate in Japan.