Forests cover a large area of the Scandinavian countries, and forest industries are economically important to these countries. Urban, managed or natural forests also have significant amenity value. These forests are threatened by introductions of Phytophthora plant pathogens. Compared to the well-studied P. infestans, tree pathogenic Phytophthoras such Phytophthoras plurivora and Phytophthoras cactorum are less well characterized and little is known about the mechanisms of resistance to Phytophthoras in trees. Both pathogens have broad host range and infect mainly beech and poplar. They can also cause infection to varying degree on birch, pine, norway spruce, larch, oak, beech and poplar. We have recently sequenced genomes of both these pathogens. We propose to use genome data and existing global transcriptome (RNAseq) to gain a deeper understanding of tree infections by P. plurivora, and P. cactorum associated with widespread decline of beech and oak. Genome and RNA seq data will identify potential targets for disease control. We will also develop functional genetic capabilities for these pathogens in model plant species, to aid determining role(s) for effector proteins in Phytophthora-tree disease, and gain insights into tree resistance to Phytophthoras. Knowledge of pathogen biology is fundamental to exploring the nature of resistance that could be deployed to mitigate disease outbreaks in the longer term.