Elevated CO(2) alters photosynthesis, growth and susceptibility to powdery mildew of oak seedlings

Elevated CO(2) (eCO(2)) is a determinant factor of climate change and is known to alter plant processes such as physiology, growth and resistance to pathogens. Quercus robur, a tree species integrated in most forest regeneration strategies, shows high vulnerability to powdery mildew (PM) disease at the seedling stage. PM is present in most oak forests and it is considered a bottleneck for oak woodland regeneration. Our study aims to decipher the effect of eCO(2) on plant responses to PM. Oak seedlings were grown in controlled environment at ambient (aCO(2), ∼400 ppm) and eCO(2) (∼1000 ppm), and infected with Erysiphe alphitoides, the causal agent of oak PM. Plant growth, physiological parameters and disease progression were monitored. In addition, to evaluate the effect of eCO(2) on induced resistance (IR), these parameters were assessed after treatments with IR elicitor β-aminobutyric acid (BABA). Our results show that eCO(2) increases photosynthetic rates and aerial growth but in contrast, reduces root length. Importantly, under eCO(2) seedlings were more susceptible to PM. Treatments with BABA protected seedlings against PM and this protection was maintained under eCO(2). Moreover, irrespectively of the concentration of CO(2), BABA did not significantly change aerial growth but resulted in longer radicular systems, thus mitigating the effect of eCO(2) in root shortening. Our results demonstrate the impact of eCO(2) in plant physiology, growth and defence, and warrant further biomolecular studies to unravel the mechanisms by which eCO(2) increases oak seedling susceptibility to PM.