Wheat diseases present a constant and evolving threat to food security. We have little understanding as to how increased atmospheric carbon dioxide levels will affect wheat diseases and thus the security of grain supply. Atmospheric CO 2 exceeded the 400 ppmv benchmark in 2013 and is predicted to double or even treble by the end of the century. This study investigated the impact of both pathogen and wheat acclimation to elevated CO 2 on the development of Fusarium head blight (FHB) and Septoria tritici blotch (STB) disease of wheat. Here, plants and pathogens were cultivated under either 390 or 780 ppmv CO 2 for a period (two wheat generations, multiple pathogen subcultures) prior to standard disease trials. Acclimation of pathogens and the wheat cultivar Remus to elevated CO 2 increased the severity of both STB and FHB diseases, relative to ambient conditions. The effect of CO 2 on disease development was greater for FHB than for STB. The highest FHB disease levels and associated yield losses were recorded for elevated CO 2-acclimated pathogen on elevated CO 2-acclimated wheat. When similar FHB experiments were conducted using the disease-resistant cultivar CM82036, pathogen acclimation significantly enhanced disease levels and yield loss under elevated CO 2 conditions, thereby indicating a reduction in the effectiveness of the defence pathways innate to this wheat cultivar. We conclude that acclimation to elevated CO 2 over the coming decades will have a significant influence on the outcome of plant-pathogen interactions and the durability of disease resistance.
