Pathogens on the Move: A 100-Year Global Experiment with Planted Eucalypts

Co-evolved plant pathogens play an important role in shaping natural ecosystems. However, plants used in agriculture and forestry have been distributed globally, and their associated pathogens have moved with them. Eucalypts constitute the largest component of global hardwood plantations, and they are increasingly plagued by numerous pathogens, all of which are inconsequential in the native forests. Eucalypts provide a particularly interesting model to study tree diseases because plantations have been established in countries where these trees are exotic but also in Australia adjacent to native eucalypt forests. These situations present opportunities for pathogen movement between the two systems. We present seven different scenarios considering pathogen movement, important disease epidemics, and biosecurity risks, illustrated with examples of well-known eucalypt pathogens and research largely from our laboratories. The overview shows that vigilant biosecurity is required to protect the biodiversity of native forests and the sustainability of eucalypt plantations.