Short-term high nighttime temperatures pose an emerging risk to rice grain failure

Abstract

Under currently projected global warming, heat waves are expected to become more frequent, and crops will be exposed to more extreme heat events during both day and night periods. It is well known that high daytime temperatures during flowering induce spikelet sterility in rice plants and directly reduce yields. However, the effects of short-term heat stress at night have not been well documented. Here, we investigated the effects of 1- to 3-night high nighttime temperatures at anthesis on rice spikelet fertility. We found that a single night high temperature of ∼32 °C just before anthesis induced spikelet sterility even in the absence of high daytime temperature. Fertile grain number was significantly decreased by a 3-night exposure to high temperatures of ≥30 °C, much lower than the reported threshold of 35 °C for heat-induced sterility during the daytime. Moreover, high nighttime temperature substantially exacerbated the sterility induced by high daytime temperature. These results indicate that short periods of high nighttime temperatures, which may be experienced during heat waves, will increase the risk of heat damage to rice yield and increase the uncertainty in predictions of future rice production. Sensitivity to high nighttime temperature differed among cultivars but was positively correlated with their sensitivity to high daytime temperatures. This suggests that concurrent improvement of tolerance to daytime and nighttime high temperatures may be possible through breeding.