**AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** THE EVOLUTIONARY INTERACTIONS OF PHAGES AND THEIR BACTERIAL HOSTS HAS BEEN STUDIED EXTENSIVELY IN THE LAB, BUT FEW STUDIES HAVE EXAMINED THESE DYNAMICS IN NATURE. THE OVERARCHING AIM OF THIS PROJECT IS TO EXAMINE THE ROLE OF PHAGES IN BACTERIAL COMMUNITY TURNOVER AND DISEASE USING A NOVEL PEAR TREE DISEASE SYSTEM (CALLERY 'BRADFORD' PEAR TREES INFECTED WITH THE AGRICULTURALLY RELEVANT PATHOGEN ERWINIA AMYLOVORA). THROUGH THE TIGHT INTEGRATION OF TEACHING AND RESEARCH, THE COMBINATION OF HIGH-THROUGHPUT CULTURE-DEPENDENT SCREENING AND CULTURE-INDEPENDENT 'OMICS' APPROACHES WILL ALLOW FOR TRACKING OF BACTERIA-PHAGE DYNAMICS OVER BOTH SHORT (MONTHLY) AND LONG (YEARLY) TIME SCALES. THE PROJECT WILL BUILD AN UNPARALLELED TEMPORAL AND SPATIAL DATASET ON PHAGE HOST RANGE WITH WHICH TO EXAMINE THE ROLE OF PHAGES (BOTH LYTIC AND TEMPERATE) IN BACTERIAL COMMUNITY ASSEMBLY, STABILITY, AND PATHOGEN INVASION. THE WORK COMBINES BOTH CLASSIC EMPIRICAL APPROACHES TO STUDY THE STRENGTH AND SCALE OF PHAGE ADAPTATION WITH NEW COMPUTATIONAL APPROACHES TO PREDICT HOW PHAGES SHAPE MICROBIAL NETWORKS. THE DATA GENERATED WILL OFFER UNPRECEDENTED INSIGHT INTO BACTERIA-PHAGE DYNAMICS IN NATURE AND VIRAL HOST RANGE EVOLUTION IN AN AGRICULTURALLY IMPORTANT DISEASE SETTING. THE RESEARCH FURTHER DEVELOPS BASIC UNDERSTANDING OF PLANT MICROBIOMES AND VIROMES, AND WILL SUPPORT THE DEVELOPMENT OF A NEW DISEASE ECOLOGY MODEL SYSTEM THAT IS BOTH AMENABLE TO UNDERGRADUATE TRAINING IN THE MICROBIOME FIELD AND UNIQUE IN ITS POTENTIAL TO GAIN INSIGHT INTO VIROME-MICROBIOME INTERACTIONS IN BOTH HEALTH AND DISEASE. THE KNOWLEDGE GAINED, AS WELL AS PHAGES ISOLATED AND CHARACTERIZED, WILL HELP INFORM NOVEL METHODS OF SUSTAINABLE DISEASE CONTROL.