Impacts of ozone stress on stem lodging characteristics of different indica and japonica rice cultivars

Ozone (O-3) stress inhibits rice growth and development, resulting in yield loss and poor quality. However, the effect of ozone stress on the lodging resistance of rice stems has scarcely been reported. In this study, three indica rice cultivars and three modern japonica rice cultivars were treated with high O-3 concentration (100 ppb) while a gas fumigation platform was used in the indoor control (about 10 ppb). The influence of O-3 stress on lodging resistance was investigated in 2016 and 2017. Ozone stress reduced the in situ pushing resistance of intact plants by 40% and single stems by 32.0%. The breaking resistance of the third, fourth, and fifth internodes from the top of the rice stem was, respectively, reduced by 24.0%, 25.1%, and 33.6%, on average. The O-3-induced reduction in the basal internode morphological characteristics was associated with the reduced cross-sectional area, maximum and minimum stem diameter, dry weight per unit length, length, dry weight, and culm wall thickness. Among these characteristics, the largest reduction was exhibited by internode dry weight (-43.1%), while the lowest reduction was observed for culm wall thickness (-9.7%). The O-3 induced a significantly higher reduction in basal internode characteristics of indica compared with the japonica rice, with a larger effect in the lower internode than the upper internode, indicating a significant interaction between O-3 and rice cultivar and internode position. Statistical analysis revealed a significant positive linear correlation between the response of in situ pushing resistance of rice under O-3 stress and the response of basal internode breaking resistance, cross-sectional area, and dry weight per unit length. Ozone stress significantly reduced the lodging resistance in the rice stem, which is primarily associated with the thinning and poor filling of the basal internodes, and the O-3 impacts varied with cultivars and internode positions, but were similar between the two years. These results provide a scientific reference for the study of lodging resistance regulation of rice under high O-3 concentrations.