Potential distribution of invasive boxwood blight pathogen (Calonectria pseudonaviculata) as predicted by process-based and correlative models

Boxwood blight, caused by the ascomycete fungi Calonectria pseudonaviculata and C. henricotiae , is an emerging plant disease of boxwood ( Buxus spp.) that has had devastating impacts on the health and productivity of boxwood in both the horticultural sector and native ecosystems. In this study, we predicted the potential distribution of C. pseudonaviculata at regional and global scales and explored how climatic factors shape its known range limits. Our workflow combined multiple modeling algorithms to enhance the reliability and robustness of predictions. We produced a process-based climatic suitability model in the CLIMEX program and combined outputs of six different correlative modeling algorithms to generate an ensemble correlative model. All models were fit and validated using an occurrence record dataset (N = 292 records from 24 countries) comprised of positive detections of C. pseudonaviculata from across its entire known invaded range. Evaluations of model performance provided validation of good model fit for all models. A consensus map of CLIMEX and ensemble correlative model predictions indicated that not-yet-invaded areas in eastern and southern Europe and in the southeastern, midwestern, and Pacific coast regions of North America are climatically suitable for establishment. Most regions of the world where Buxus and its congeners are native are also at risk of establishment, which suggests that C. pseudonaviculata should be able to significantly expand its range globally if susceptible hosts exist. Our findings provide the first insight into the global invasion threat of boxwood blight, and are valuable to stakeholders who need to know where to focus surveillance efforts for early detection and rapid response measures to prevent or slow the spread of the disease.