Effects of Atmospheric CO₂ Level on the Metabolic Response of Resistant and Susceptible Wheat to Fusarium graminearum Infection

Rising atmospheric CO 2 concentrations and associated climate changes are thought to have contributed to the steady increase of Fusarium head blight (FHB) on wheat. However, our understanding of precisely how elevated CO 2 influences the defense response of wheat against Fusarium graminearum remains limited. In this study, we evaluated the metabolic profiles of susceptible (Norm) and moderately resistant (Alsen) spring wheat in response to whole-head inoculation with two deoxynivalenol (DON)-producing F. graminearum isolates (DON + ), isolates 9F1 and Gz3639, and a DON-deficient (DON − ) isolate (Gzt40) at ambient (400 ppm) and elevated (800 ppm) CO 2 concentrations. The effects of elevated CO 2 were dependent on both the Fusarium strain and the wheat variety, but metabolic differences in the host can explain the observed changes in F. graminearum biomass and DON accumulation. The complexity of abiotic and biotic stress interactions makes it difficult to determine if the observed metabolic changes in wheat are a result of CO 2 -induced changes in the host, the pathogen, or a combination of both. However, the effects of elevated CO 2 were not dependent on DON production. Finally, we identified several metabolic biomarkers for wheat that can reliably predict FHB resistance or susceptibility, even as atmospheric CO 2 levels rise.