Breeding targets for heat-tolerant rice varieties in Japan in a warming climate

The breeding of heat-tolerant (HT) varieties is considered an effective adaptation measure to reduce the impacts of global warming on crops. However, little is known about how much heat tolerance needs to be attained in the breeding of HT varieties and by when the HT varieties should be introduced in a warming climate. Here, we assessed the effect of the introduction of HT rice varieties on the incidence of low-quality rice grains (chalky rice grain, CRG, as a result of high temperatures), and formulated a breeding target for rice in Japan, where high incidence of CRG is already a concern. Varieties with a 3 degrees C higher temperature tolerance should be bred and introduced until the 2040s under representative concentration pathways (RCPs) 2.6 and 8.5, in the pessimistic scenario, considering the uncertainties in climate models and an impact assessment model, which were large. In the median case, varieties with a 1 and 2 degrees C higher temperature tolerance are needed until the 2040s under RCPs 2.6 and 8.5, respectively. The findings revealed necessary efforts in breeding research and programs under conditions of global warming.