Physicochemical characteristics of lodging susceptibility of rice cultivars in response to ozone exposure

High tropospheric ozone concentrations reduce rice yield and grain quality, which imposes a serious threat to food security in Asia. This study aimed at determining the effect of ozone on rice lodging, an unpredictable constraint for achieving high yield and good quality in rice production under climate change. Two rice cultivars with different ozone sensitivity were exposed to ozone concentration of 80 ppb (8 h per day) and control conditions (13 ppb) in natural-light fumigation chambers from tillering to maturity. The pushing resistance of intact plants and the lodging-related culm traits were examined. Ozone exposure significantly decreased the in-situ pushing resistance of intact plant or single culm in the ozone-sensitive cultivar YD6, but had no effects in the ozone-tolerant cultivar WYJ27. Ozone reduced breaking resistance and bending moment to a similar magnitude, resulting in no change of lodging index when averaged across all rice basal internodes. In general, WYJ27 was less responsive to ozone than YD6. Negative ozone effects on lodging-related culm traits of YD6 included reductions in the internode dry weight as well as the dry weight per unit internode length, decreases in internode diameter, cross section area and culm wall thickness of basal internodes, and reduced concentrations of soluble sugar and starch. Correlation analysis indicated that ozone-induced decrease in culm strength of YD6 was mainly attributed to the thinner internodes and the smaller culm density due to less nonstructural carbohydrate deposition. The ozone-sensitivity of YD6 was confirmed by its high yield reduction of 25 %, caused by an 11 % decrease in spikelet number per panicle and a 10 % decrease in fulfilled grain weight. The results suggested that rice ozone sensitivity in yield was in consistent with that in stem strength, which could result in no change of lodging index under greenhouse conditions. The realistic lodging susceptibility of these cultivars in response to ozone pollution in open paddy fields, where rice was often subjected to wind and rain during ripening stage, needs further investigation.