Effects of Atmospheric CO₂ Levels on the Susceptibility of Maize to Diverse Pathogens

Rising atmospheric CO₂ has significant implications for crop productivity and food security. Based on studies in C3 plants, elevated CO₂ (eCO₂) can shape plant-pathogen interactions, although the outcomes are often variable. The question of how eCO₂ 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 CO₂ (aCO₂, 420 ppm) and eCO₂ (550 ppm) with bacterial, viral, fungal, and oomycete pathogens. Plants grown in eCO₂ 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 eCO₂-responsive defense mechanisms, and they highlight a critical need to understand how eCO₂ will impact plant responses to microbes, pests, and abiotic stresses under future conditions.