Combined Effects of Elevated Ozone and Air Temperature on Grain Quality in 17 Cultivars of Rice

Abstract

The tropospheric ozone concentration is expected to increase with elevation of the air temperature under global warming. To estimate the ozone threat to appearance quality of Japanese rice grains under global warming conditions, we conducted ozone exposure combined with a temperature rise of 1.7℃ in open-top chambers using 17 Japanese cultivars. The fraction of chalky grains in most cultivars grown in northern Japan significantly increased by the elevated ozone and combination of elevated ozone and air temperature. Significant positive correlations were found between the ozone dose during grain ripening period and fraction of chalky grains in ‘Satonoyuki’ and ‘Koshihikari’ with and without air temperature elevation. The combined effects of air temperature and ozone elevation were additive in ‘Koshihikari’, but were greater than additive in ‘Satonoyuki’. A two-way analysis of variance showed that the ozone-temperature interaction in the formation of chalky grains was not identified in some rice cultivars investigated here, suggesting that there is varietal difference in the mechanism of chalky grain formation by ozone under the elevated air temperature condition. Moreover, there is significant negative correlation between amylose content in brown rice and the rate of chalky grain under elevated ozone. This suggests that the appearance quality of grains in rice cultivars with lower amylose content tend to be deteriorated by elevated ozone, and the deterioration of grain quality with ozone is enhanced even further by the temperature elevation.