Assessing the effect of elevated CO₂ on wheat leaf rust severity: insights from a free-air carbon dioxide enrichment (FACE) experiment

The continuous increase in atmospheric carbon dioxide (CO₂) concentrations is a major driver of global climate change and may alter plant growth and host-pathogen interactions. Understanding how elevated CO₂ affects disease development is therefore important for future crop production and resistance screening. This study investigated the effect of elevated CO₂ on wheat leaf rust (Puccinia triticina) in Central European winter wheat genotypes under field conditions.

Free Air Carbon Dioxide Enrichment (FACE) field experiments were conducted over two growing seasons, exposing winter wheat to an atmospheric CO₂ concentration of approximately 600 ppm. Leaf rust development was assessed using the Area Under the Disease Progress Curve (AUDPC) and Average Ordinate (AO). Genotypic effects, CO₂ treatment effects and their interaction were analysed across the tested genotypes and growing seasons.

Elevated CO₂ was associated with a general tendency towards higher leaf rust severity, although the magnitude of this response varied between growing seasons and genotypes. Genotype effects were highly significant, whereas the genotype × CO₂ interaction was comparatively weak, providing limited evidence for differential responses among the tested genotypes. Under the conditions of this FACE experiment, the relative ranking of genotypes for leaf rust severity was largely maintained under elevated CO₂.

The results indicate that elevated CO₂ may affect the expression of wheat leaf rust resistance, while the relative differences among genotypes remained largely consistent under the tested conditions. However, the limited number of independent CO₂ treatment environments, particularly following the exclusion of one elevated CO₂ ring in 2023, restricts the strength of treatment-level inference. The findings should therefore be interpreted as observations specific to the experimental conditions rather than as general evidence for stable leaf rust resistance under elevated atmospheric CO₂. Nevertheless, they highlight the importance of considering changing atmospheric CO₂ concentrations when evaluating and screening disease resistance in future wheat breeding programmes.