Even though powdery mildews as a group are among the most economically important diseases of plants, with over 900 species infecting more than 6000 plant species, relatively little is known about these pathogens. Via the Joint Genome Institute – Community Sequencing Project, our group of collaborators will sequence the genomes of powdery mildew species from each of the five tribes of Erysiphaceae for a total of 11 genomes. This study will address scientific questions about the powdery mildew underlying host specialization (e.g., effector diversity, ability to metabolize host secondary metabolites), and about the determinants of the partnership between host plant and powdery mildew required for successful infections.