Epidemiology and biology of powdery mildews and their host plants

Abstract

Powdery mildew is one of the most prevalent plant pathogens in the Pacific Northwest with over 150 different species infecting over 1000 plants. The hot, dry summers and wet, mild winters in this region are optimal for its colonization and spread. Sequencing herbarium specimens for plant pathogens, including powdery mildews, can be challenging but useful in addressing fundamental ecological, epidemiological, and phylogenetic questions in plant-pathogen interactions. In my dissertation, I reviewed the taxonomy and phylogeny of powdery mildews and developed a new sequencing protocol for sequencing herbarium specimens. Using this new sequencing protocol, I conducted a world-wide phylogenetic and taxonomic analysis on powdery mildews on Viburnum, in which I described two new species, E. viburniphila sp. nov and E. pseudoviburni sp. nov, and reduced E. hedwigii to synonymy with E. viburni; and genetically ascertained the origin and timing of an introduced plant pathogen of which Acer macrophyllum (bigleaf maple) is highly susceptible. Additionally, I evaluated 126 plant species within Asteraceae to measure the role of host plant morphological traits and evolutionary history on their suitability and susceptibility to the powdery mildew, Golovinomyces latisporus, and observed that phylogenetic structure, and not plant morphology, is the most consistent predictor of host susceptibility to pathogens. Examining genetic data of ancient herbarium specimens and quantifying host evolutionary history can be useful approaches in deciphering the invasion dynamics and potential impacts of non-native plant pathogens, and addressing ecological, evolutionary and pathological questions related to emerging plant pathogen epidemics.