** AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** GLOBAL TRADE AND CLIMATE CHANGE ACCELERATE AND COMPOUND THE EMERGENCE OF PLANT PATHOGENS AND IMPACTS ON NATURAL AND MANAGED ECOSYSTEMS. PHYTOPHTHORA PLUVIALIS IS A FOLIAR PATHOGEN OF CONIFER TREES THAT HAS REPEATEDLY EMERGED IN THE UNITED STATES (US) AND INVADED NEW ZEALAND (NZ) AND MORE RECENTLY THE UNITED KINGDOM (UK). ITS EMERGENCE HAS CAUSED SEVERE EPIDEMICS ON ECONOMICALLY IMPORTANT CONIFER TREES IN BOTH PLANTATIONS AND WILD LAND FORESTS. IN ITS MOST RECENT EMERGENCE, P. PLUVIALIS NOT ONLY JUMPED TO A NEW HOST BUT WAS ASSOCIATED WITH A DEVASTATING SHIFT IN DISEASE ETIOLOGY. STUDYING P. PLUVIALIS IS OF DIRECT RELEVANCE IN SUPPORT OF GOALS TO IMPROVE THE LONG-TERM SUSTAINABILITY AND COMPETITIVENESS OF U.S. AGRICULTURAL SYSTEMS. THE CHANGE IN DISEASE ETIOLOGY IS OF PARTICULAR CONCERN. ITS POTENTIAL EFFECTS ON THE FOREST INDUSTRY IN THE PACIFIC NORTHWEST OF THE US ARE SIGNIFICANT. WESTERN HEMLOCK AND DOUGLAS-FIR, THE TWO MAIN HOSTS OF THIS PATHOGEN, MAKE UP MOST OF THE CROP TREES PLANTED ON THE 8.1 MILLION ACRES OF PRIVATE INDUSTRIAL FOREST LAND. WE AIM TO: 1) CHARACTERIZE THE VARIATION IN SUSCPETIBILITY TO P. PLUVIALIS WITHIN AND AMONG POPULATIONS OF DOUGLAS-FIR AND WESTERN HEMLOCK; 2) USE PHYLOGENY GUIDED PHENOTYPING OF PATHOGEN POPULATIONS; AND 3) DEVELOP AND DEPLOY A MULTIPLEX CRISPR BASED SHERLOCK ASSAY TO DETECT MAJOR LINEAGES OF P. PLUVIALIS IN THE FIELD. THESE AIMS WILL ALLOW US TO EVALUATE AND ATTENUATE THE RISK OF P. PLUVIALIS TO WESTERN HEMLOCK AND DOUGLAS-FIR FORESTS IN THE USA.