Widespread Latent Presence of <i>Cryptostroma corticale</i> in Sycamore Maple in France

ABSTRACT Increasingly frequent drought events can favour forest disease emergence. Sooty bark disease (SBD) of Acer pseudoplatanus (sycamore maple) is a good example of this phenomenon. Records of its causal agent, Cryptostroma corticale , invasive in Europe, have increased since the 2000s in central and southern Europe. The pathogen is found asymptomatically in host tissues and switches to a pathogenic lifestyle following abiotic stress. This latent phase hinders the pathogen's early detection. In this study, we assessed the prevalence of C. corticale in asymptomatic trees in France. Our study covered six regions, each including a city and its nearby peri‐urban and forested ecosystems, representing a human gradient of influence. We assessed the pathogen's presence in 540 wood samples from asymptomatic maple trees by using real‐time PCR. The prevalence was 13.6%, across all plots. The pathogen appears to be widespread in the natural sycamore maple stands of France, increasing the risk of disease development following future drought events. Host density and 3‐year accumulated water deficit best explained detection of C. corticale in asymptomatic sycamore maples. However, the detection of the fungus was not related to the level of human influence, as no significant differences were observed along the urban‐to‐forest gradient. Furthermore, C. corticale was detected in asymptomatic hosts even in regions with limited reports of SBD, indicating that the local reporting frequency of the disease does not reflect the latent presence of the pathogen.