Conditions of emergence of the Sooty Bark Disease and aerobiology of Cryptostroma corticale in Europe

The sooty bark disease (SBD) is an emerging disease affecting sycamore maple trees (Acer pseudoplatanus)in Europe. Cryptostroma corticale, the causal agent, putatively native to eastern North America, can bealso pathogenic for humans causing pneumonitis. It was first detected in 1945 in Europe, with markedlyincreasing reports since 2000. Pathogen development appears to be linked to heat waves and droughtepisodes. Here, we analyse the conditions of the SBD emergence in Europe based on a three-decadal timeseries data set. We also assess the suitability of aerobiological samples using a species-specific quantitativePCR assay to inform the epidemiology of C. corticale, through a regional study in France comparing twoyear aerobiological and epidemiological data, and a continental study including 12 air samplers from sixcountries (Czechia, France, Italy, Portugal, Sweden and Switzerland).We found that an accumulated water deficit in spring and summer lower than -132 mm correlateswith SBD outbreaks. Our results suggest that C. corticale is an efficient airborne pathogen which can disperse its conidia as far as 310 km from the site of the closest disease outbreak. Aerobiology of C. corticalefollowed the SBD distribution in Europe. Pathogen detection was high in countries within the host nativearea and with longer disease presence, such as France, Switzerland and Czech Republic, and sporadic inItaly, where the pathogen was reported just once. The pathogen was absent in samples from Portugal andSweden, where the disease has not been reported yet. We conclude that aerobiological surveillance caninform the spatial distribution of the SBD, and contribute to early detection in pathogen-free countries.