Effects of atmospheric CO2 levels on the susceptibility of maize to diverse pathogens

Authors: KHWANBUA, EKKACHAI - Iowa State University; QI, YUNHUI - Dana-Farber Cancer Institute; SSENGO, JOHN - Iowa State University; LIU, PENG - Iowa State University; Graham, Michelle; WHITHAM, STEVEN - Iowa State University

Submitted to: bioRxiv
Publication Type: Pre-print Publication
Publication Acceptance Date: 1/2/2026
Publication Date: 1/2/2026
Citation: Khwanbua, E., Qi, Y., Ssengo, J., Liu, P., Graham, M.A., Whitham, S.A. 2026. Effects of atmospheric CO2 levels on the susceptibility of maize to diverse pathogens. bioRxiv. https://doi.org/10.64898/2025.12.31.697224.
DOI: https://doi.org/10.64898/2025.12.31.697224

Interpretive Summary: Carbon dioxide (CO2) is one of the most influential molecules affecting plant physiology, and plants are exquisitely sensitive to their concentration in the air. Rising atmospheric CO2 is predicted to impact crop productivity and food security in different ways, depending on which photosynthetic pathway (C3 or C4) a given plant species uses to fuel growth and production. Photosynthesis in C3 plants, such as rice, soybean and wheat, is enhanced in elevated CO2 (eCO2). C3 photosynthesis is best suited for moderate conditions and becomes less efficient in dry or hot environments. C4 plants, including maize, sorghum and sugar cane, have adapted a more efficient photosynthetic pathway that protects the plant during unfavorable conditions, but is not enhanced by eCO2. Based on studies in C3 plants, eCO2 can also impact 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 current, ambient CO2 (aCO2) and eCO2 with bacterial, viral, fungal, and oomycete pathogens. As with C3 plants, we observed variable responses. For example, maize plants grown in eCO2 were more susceptible to sugarcane mosaic virus, suggesting compromised antiviral defenses. In contrast, plants grown in eCO2 were less susceptible to the bacteria Clavibacter nebraskensis, likely due to 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. Developing strategies to protect the health of maize in the long-term will help U.S. growers and producers anticipate and mitigate future disease problems to ensure safe, abundant and affordable food, feed and fiber for American consumers.

Technical Abstract: Rising atmospheric CO2 has profound 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 eCO2responsive 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.