Responses of grain filling in spring wheat and temperate-zone rice to temperature: Similarities and differences

•Wheat (Triticum aestivum L.) and rice (Oryza sativa L.) as starch-grain crops have different optimal temperatures for grain yield.•The potential grain growth rate in both crops was indicated by a similar logistic curve of cumulative temperatures after anthesis.•Estimated grain yield by an assimilate limited and grain potentiality model showed a lower optimal temperature in wheat than in rice.•The lower optimal temperature in wheat mainly results from a higher sensitivity of assimilation to an increase in temperature.•From our results, the grain-filling in wheat under elevated temperatures is expected to be improved by assimilation resistance to temperature.