Combining permanent aerobiological networks and molecular analyses for large-scale surveillance of forest fungal pathogens: A proof-of-concept

Forest disease management relies principally on a preventive approach in which epidemiological surveillance plays a crucial role. However, efficient and cost-effective surveillance methods are not currently available for large spatial scales. Nevertheless, aerobiological networks have been set up for several decades in many countries to monitor pollen dispersal and provide real-time assessments of allergenic risk. Here, we suggest that the same approach could be used for the surveillance of forest pathogens. Using molecular methods, we analysed samples from 12 sites of the French aerobiological network, at different dates. Both metabarcoding by high-throughput sequencing (using two markers and two different bioinformatics approaches) and real-time PCR targeting eight important forest pathogens were conducted. To validate the approach, temporal and spatial trends of spore detection were compared with field disease data. The metabarcoding approach demonstrated that many fungal plant pathogens could be found in aerobiological samples. Moreover, five of the eight targeted forest pathogens were detected by real-time PCR, with temporal and spatial trends of spore capture consistent with field data. In particular, Hymenoscyphus fraxineus was detected at high frequency in aerobiological samples in the areas where ash dieback has been present for the longest period of time, and at lower frequency in areas with more recent invasion. Spore detection of seasonal pathogens showed a temporal pattern similar to that of disease reports. Overall, our study provides a proof of concept that permanent aerobiological networks combined with molecular methods may provide a useful tool for large-scale surveillance of forest pathogens.