Open-Top Chambers with Solar-Heated Air Introduction Tunnels for the High-Temperature Treatment of Paddy Fields

Abstract

The quality of rice grain has been deteriorating as a result of the high temperature during the ripening stage caused by global warming. Easy and effective methods of high-temperature treatment are essential for the analysis of high-temperature tolerance and to screen for tolerant strains. We have improved the open-top chamber (OTC) by adding a solar-heated air introduction tunnel (SAT). The air is warmed by solar radiation as it passes through the tunnel and then flows into the OTC. The increase in temperature in the OTC-SAT was powered by solar radiation. Thereby, the temperature in OTC-SAT rose during the day according to the distance from the air intake (the nearer, the higher). A more uniform increase in temperature of approximately 1.2°C in the daytime was achieved by attaching a sloping wall and funnel-shaped air exhaust tunnel to the OTC-SAT to improve the air flow. The area of the high-temperature treatment was easily increased by increasing the width of the OTC-SAT; this finding might be useful for screening a large number of strains. The increase in the percentage of chalky grains by the use of OTC-SAT was similar to that obtained with the other treatment methods; the OTC-SAT will thus be useful for investigating high-temperature tolerance during the ripening stage, particularly in areas where the wind direction is stable. The use of an OTC with a funnel-shaped tunnel on both the air entrance and the air exit sides might be useful in areas where the wind direction is often reversed.