Effects of Atmospheric CO ₂ Levels on the Susceptibility of Maize to Diverse Pathogens

Rising atmospheric CO 2 has significant implications for crop productivity and food security. Based on studies in C3 plants, elevated CO 2 (eCO 2 ) can shape plant‐pathogen interactions, although the outcomes are often variable. The question of how eCO 2 influences immunity and disease development in C4 plants, such as the globally important cereal crop maize ( Zea mays L.), has not been systematically examined. We challenged maize plants grown under ambient CO 2 (aCO 2 , 420 ppm) and eCO 2 (550 ppm) with bacterial, viral, fungal, and oomycete pathogens. Plants grown in eCO 2 were more susceptible to sugarcane mosaic virus, suggesting compromised antiviral defenses, less susceptible to Clavibacter nebraskensis , Exserohilum turcicum , and Colletotrichum graminicola , and susceptibility to Puccinia sorghi and Pythium sylvaticum was unchanged. Reduced susceptibility to C. nebraskensis was associated with enhanced basal immune responses. These results establish a foundation for dissecting eCO 2 ‐responsive defense mechanisms, and they highlight a critical need to understand how eCO 2 will impact plant responses to microbes, pests, and abiotic stresses under future conditions.