Cork harvest planning and climate: High air humidity favors availability of airborne inoculum of Diplodia corticola

The canker disease caused by Diplodia corticola is one of the most important emerging pathologies of cork oak (Quercus suber) in western Europe. The fungus is dispersed by borer insects, although it is also thought that the spores can be dispersed by wind and rain. The aim of this study was to evaluate the presence of airborne inoculum of D. corticola in managed cork oak stands during cork harvesting season. Semi-passive spore traps were set in eight sampling plots in Catalonia (north-eastern Spain) in summer of 2020. Traps were replaced every week and the number of D. corticolas spores per sampling event was estimated based on a specific nested-qPCR protocol. Spatial-temporal distribution of airborne inoculum accumulation along sampling areas was analyzed using generalized additive models (GAMs). The availability of airborne inoculum resulted rather low with noticeable accumulation peaks in some of the sampled areas. The fitted GAM revealed a positive effect of high air humidity during the sampling period on the availability of spores. This study represents the first attempt to model the spore release of this emerging pathogen, and it provides insights for developing D. corticola canker control strategies based on the precise timing of cork harvesting operations.