BACTERIOCINS ARE PROTEINACEOUS TOXINS UBIQUITOUS AMONG PLANT PATHOGENS, THAT ARE HYPOTHESIZED TO PLAY AN IMPORTANT ROLE IN FACILITATING COLONIZATION OF LEAF SURFACES WITHIN A COMMUNITY CONTEXT. HOWEVER, THERE IS MINIMAL EMPIRICAL RESEARCH THAT HAS ADDRESSED THE ROLE OF THESE TOXINS DIRECTLY, WHICH LIMITS OUR UNDERSTANDING OF A POTENTIALLY CRITICAL COMPETITIVE STRATEGY EMPLOYED BY FOLIAR PATHOGENS, BECAUSE FOLIAR PATHOGENS MUST FIRST INVADE, PERSIST, PROLIFERATE WITHIN AN EPIPHYTIC CONTEXT PRIOR TO INVASION INTO THE LEAF INTERIOR. THIS PROPOSAL DESCRIBES A PRE-DOCTORAL RESEARCH PROJECT WITH WELL-DEVELOPED TRAINING AND MENTORING ACTIVITIES PROPOSED BY PD, MARY SMITH, A PHD CANDIDATE IN PLANT PATHOLOGY AT PENNSYLVANIA STATE UNIVERSITY WITH DR. KEVIN HOCKETT SERVING AS THE PRIMARY MENTOR FOR RESEARCH. THIS RESEARCH PROJECT SEEKS TO INVESTIGATE THE DIRECT ROLE BACTERIOCINS PLAY DURING COLONIZATION AND EPIPHYTIC SURVIVAL USING GROWTH CHAMBER MICROBIOME TRANSPLANT EXPERIMENTS WITH MODEL PSEUDOMONAS SYRINGAE PV. TOMATO (PTO) STRAIN, PT23, USING TREATMENTS DESIGNED TO MIMIC NICHE INVASION AND DEFENSE TO PINPOINT WHEN BACTERIOCINS OF PTO PROVIDE THE LARGEST COMPETITIVE ADVANTAGES BY MEASURING DISEASE SEVERITY, PATHOGEN LOAD, AND MICROBIAL COMMUNITY COMPOSITION. THIS PROJECT ADDRESSES THE PRIORITY AREA OF "PLANT HEALTH AND PRODUCTION AND PLANT PRODUCTS". RELEVANCE OF THIS PROJECT'S GOALS TO THE PREDOCTORAL PROGRAM WILL BE THE DEVELOPMENT OF THE PDS SKILLS TO PERFORM ORIGINAL RESEARCH IN PLANT PATHOLOGY AND MICROBIAL ECOLOGY. THIS PROJECT IS RELEVANT TO THE GOALS OF THE EWD PROGRAM BECAUSE IT WILL INCREASE THE KNOWLEDGE OF THE ECOLOGICAL RELATIONSHIPS BETWEEN PLANT PATHOGEN, P. SYRINGAE, AND OTHER MICROBES IN THE PHYLLOSPHERE IMPORTANT FOR PLANT HEALTH.