Effect of ozone stress on yield characteristics of indica-japonica hybrid rice Yongyou 538 in two consecutive growing seasons

The hybrid rice cultivar Yongyou 538 (Y538) was exposed to 100 ppb ozone (O3) and control conditions throughout the cropping seasons in 2016?2017 in Yangzhou, China. The average daily maximum temperature during reproductive the growth stage (mid-August) of Y538 in 2016 was 3.6 ?C higher than that in 2017. The heading stage of Y538 was reached 6.5 days earlier in the control than in the high-O3 treatments. Ozone stress decreased plant height and tiller number at all growth stages, and the O3?induced reductions in these two parameters were gradually increased with plant development. Compared to the control, O3 stress significantly decreased yield by an average of 29.9 %, and by 35.2 and 24.0 % in 2016 and 2017, respectively. Averaged across 2 years, O3 stress caused slight reductions in both panicle number (PN) and filled grain weight (FGW). However, spikelet number per panicle (-9.6 %, SNP) and filled grain percentage (-17.5 %, FGP) showed significant reductions due to O3 exposure, while O3 stress increased empty grain percentage (EGP) and incompletely-filled grain percentage (IGP) by 72.9 and 80.0 %, respectively, when averaged across 2 years. A significant interaction of O3 by year or grain position in a panicle was observed on yield, FGP, EGP, and IGP, as the changes in 2016 were more significantly affected than those in 2017; grains at lower parts of the panicle were more affected than those at upper parts. Ozone stress significantly reduced the above ground dry weight of rice at maturity in 2 years by an average of 18.3 %, which was mainly related to the decrease in stem (-19.3 %) and panicle weight (-22.9 %), while no O3 effect was detected for leaf weight. Ozone stress significantly increased the ratio of leaf to aboveground dry weight by 23.4 % when averaged across 2 years, while the ratio of stem or panicle showed a declining trend. Correlation and path analysis showed that yield loss due to O3 exposure was closely related to the decreases in FGP (especially the middle and lower parts of the panicle) and SNP. Ozone treatment of 100 ppb significantly decreased the productivity of Y538, and the high temperature in the reproductive growth period would further exacerbate the damage caused by O3, leading to substantial yield losses.

Automated summary

The hybrid rice cultivar Yongyou 538 (Y538) experienced significant yield reductions under high O3 stress, with negative impacts on plant growth and grain development.