The potential global geographical distribution of Citrus Black Spot caused by Guignardia citricarpa (Kiely): likelihood of disease establishment in the European Union

This study represents a climatic modelling approach towards assessing the risk that Citrus Black Spot (CBS) will spread to regions of the world where the disease does not occur. Globally, CBS is widespread, but is absent within countries of the European Union (EU) and presently barriers to the trade of citrus fruit are in place to restrict the possible introduction of the pathogen Guignardia citricarpa Kiely. The objective of this study was to evaluate the climatic suitability of the European climate for the establishment of the pathogen and persistence of the disease. For this purpose, the CLIMEX model was used, which allows for the prediction of the potential geographical distribution of a species using its observed geographical distribution. In this study, the climatic requirements of CBS were inferred from the distribution thereof in South Africa and Australia. The model output reflected the current known distribution of the pathogen around the world and indicated that climate provides a barrier to the establishment of the disease in Europe. The potential distribution of CBS was mainly limited by cold conditions. A global map was produced which indicates localities where the climate is suitable for the potential establishment of the pathogen.