Ethylenediurea (EDU) protects inbred but not hybrid cultivars of rice from yield losses due to surface ozone.

The rising concentration of ground-level ozone (O3) reduces crop yield via increased oxidative stress. Application of ethylenediurea (EDU) protects plants from O3 and could thereby serve as a means to estimate the crop yield losses due to ambient O3 (AO3). However, no study but a few exceptions has ever compared the yield loss estimates from EDU application with those from O3 elevation experiments. Here, we estimated yield loss to AO3 in rice cultivars across the 3 types, indica, japonica, and hybrid, by an EDU application in the field, and compared the yield losses with those estimated with dose-response relationships based on O3 elevation experiments. Relative yield loss (RYL) in the EDU application was estimated at 16% across the rice types on an assumption of a 100% efficiency for protection of crop yield by EDU. This estimate of RYL was close to the 15% RYL estimated from the O3 elevation experiments when a common sensitivity to O3 is assumed across the cultivars. The rice yield loss due to AO3 was thus consistent between the two approaches supporting the idea of EDU application for the yield loss estimation. When only hybrids are focused, however, the RYL from EDU application (16%) was much lower than the 34% RYL from the O3 elevation experiments, which indicates only a 37% yield protection by EDU in the hybrid rice. The incomplete protection by EDU and its genetic variability indicates the need to quantify the efficiency of protection from AO3-induced yield loss as estimated with O3 manipulating experiments.