** AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** FIRE BLIGHT, CAUSED BY THE BACTERIUMERWINIA AMYLOVORA, IS THE MOST ECONOMICALLY IMPORTANT BACTERIAL DISEASE OF APPLES. CONTROL METHODS ARE LIMITED AND BREEDING RESISTANT VARIETIES CAN TAKE DECADES DUE TO APPLE'S LONG JUVENILE PERIOD (TIME TO FLOWERING). ROOTSTOCKS AND THEIR ROOT SYSTEM ARCHITECTURE (RSA), THE CONFORMATION OF ROOTS IN SPACE, PROVIDE AN ALTERNATIVE, SUSTAINABLE DISEASE MANAGEMENT STRATEGY. PREVIOUS RESEARCH REVEALED A CORRELATION BETWEEN FINE ROOTS AND DISEASE SEVERITY. THE MECHANISMS UNDERLYING THIS INTERACTION, AND THE INTERACTION BETWEEN ROOTS AND FOLIAR PATHOGENS GENERALLY, ARE NOT UNDERSTOOD. THIS PROJECT AIMS TO INVESTIGATE THE LINK BETWEEN ROOT SYSTEM ARCHITECTUREAND FIRE BLIGHTIN THREE WAYS. THE IMPACT OF NUTRIENT UPTAKE, WHICH FINE ROOTS ARE PRIMARILY RESPONSIBLE FOR, ON DISEASE SEVERITY, DEFENSE GENE EXPRESSION, AND BACTERIAL REPRODUCTION WILL BE EXPLORED. DIFFERENTIAL EXPRESSION ANALYSIS BETWEEN FINE AND COARSE ROOTS, BOTH CONSTITUTIVELY AND IN RESPONSE TO INFECTION, WILL BE CONDUCTED TO EXAMINE MECHANISMS UNDERLYING THIS INTERACTION. LASTLY, THIS PROPOSAL WILL TEST IF ROOT GROWTH, A HALLMARK OF FINE ROOTS, INCREASES INFECTION SEVERITY. THE PROPOSED RESEARCH WILL ELUCIDATE WAYS THAT APPLE ROOTS RESPOND TO INFECTION AND WILL INCREASE THE LIMITED KNOWLEDGE OF THE ROLE OF ROOTS IN DISEASE DEVELOPMENT.