Alien forest pathogens : Phytophthora species are changing world forests

Phytophthora is a genus of aquatic plant pathogens well known as disease agents in agriculture and forestry.They are water molds, Oomycetes, with swimming zoospores and thick-walled resting spores.Many species are benign in coevolved plant communities, but given the opportunity of introduction to new hosts in new environments, new opportunities for dispersal, or unexpected sexual recombination, they are causing dramatic epidemics in forests around the world.Phytophthora ramorum (cause of sudden oak death in western North America and also damaging in Europe) provides a current example, dramatically illustrating the potential of these pathogens for rapid ecological (and economic) damage.Phytophthora cinnamomi and P. lateralis are also alien to Europe and North America but with different epidemiological strategies.By comparing these three related pathogens and the different consequences of their invasions, some predictions for the future of our forests are possible.