PLANT DISEASES, CAUSED BY PLANT PATHOGENS, ARE A SOURCE OF CONSIDERABLE CROP YIELD LOSS. TO DATE, THE MOST SUSTAINABLE APPROACH TO CONTROLLING PLANT DISEASE IS THROUGH THE DEVELOPMENT AND DEPLOYMENT OF DISEASE RESISTANT CROP VARIETIES. DISEASE RESISTANT VARIETIES DISPLAY IMMUNITY BY EXPRESSING RESISTANCE (R) GENES. HOWEVER, R GENES CAN BE QUICKLY OVERCOME BY PATHOGENS IN THE FIELD DUE TO THE STRONG SELECTIVE PRESSURE. TO BEST PRESERVE THE LONGEVITY OF RESISTANCE-BASED PATHOGEN CONTROL, AND TO PROTECT GLOBAL FOOD SECURITY IN LIGHT OF PLANT DISEASE, THERE IS A NEED TO UNDERSTAND THE DRIVERS OF PATHOGEN EVOLUTION AND ADAPTATION.TO EXPLORE WHETHER PLANT HOSTS INDUCE HIGHER RATES OF PATHOGEN EVOLUTION, I WILL DEFINE THE MUTATION RATES OF THE BACTERIAL PATHOGEN XANTHOMONAS ORYZAE (XO), THE CAUSATIVE AGENT OF TWO RICE DISEASES. MUTATION RATES FOR THIS PATHOGEN ARE UNKNOWN AND THOUGHT TO BE CONSTANT. HOWEVER, MY EARLY RESULTS SUGGEST THAT MUTATION RATES OCCUR MORE WHEN THE BACTERIA ARE INSIDE RICE PLANTS. USING THE WELL-DEFINED RICE-XO SYSTEM, I WILL DEFINE HOW SUSCEPTIBLE, MODERATELY RESISTANT AND STRONGLY RESISTANT RICE PLANTS IMPACT XO MUTATION RATE. TO DO SO, I WILL DEVELOP NEW TOOLS FOR STUDYING BACTERIAL MUTATION DURING PLANT-PATHOGEN INTERACTIONS.THE ULTIMATE GOAL THE PROJECT HOPES TO ACHIEVE IS TO BETTER UNDERSTAND HOW PLANT HOSTS INFLUENCE BACTERIAL EVOLUTION VIA CHANGES TO MUTATION RATES. DEVELOPMENT OF RESISTANT CROP VARIETIES IS TIME CONSUMING. DEPLOYMENT OF RESISTANT VARIETIES IS RISKY BECAUSE PATHOGENS MAY QUICKLY OVERCOME RESISTANCE DUE TO EVOLUTION. UNDERSTANDING HOW PLANTS AFFECT BACTERIAL MUTATION RATES WILL INFORM CROP IMPROVEMENT PROGRAMS TO MOST SUSTAINABLY DEVELOP AND DEPLOY RESISTANT CROP VARIETIES. ULTIMATELY, THIS INFORMATION WILL HELP PROTECT THE GLOBAL FOOD SUPPLY FROM DAMAGE FROM PATHOGENS.