The decline in the ratio of first-grade quality rice grains has been more serious issue with the recent progressive global warming. Meanwhile a research team from NARO quantitatively assessed the superior grain appearance of 'Niji-no-kirameki' to that of the Japanese leading cultivar 'Koshihikari' as the result of a four-year survey in the heat-vulnerable regions of Japan. In addition, it was clarified that 'Niji-no-kirameki' has a possible "heat avoidance" mechanism in which the panicle temperature can be maintained cooler than 'Koshihikari' under high temperature conditions during the ripening period. It is assumed that one of the reasons for this is that the panicles are hidden in the leaves.