RUST FUNGI ARE ONE OF THE MOST SERIOUS THREATS IN THE PRODUCTION OF SMALL GRAINS. THE CROWN RUST DISEASE OF OAT (AVENA SATIVA) CAUSED BY PUCCINIA CORONATA F. SP. AVENAE (PCA) SIGNIFICANTLY IMPACTS OAT YIELD AND PRODUCTIVITY IN THE U.S. AND THROUGHOUT THE WORLD. PCA HAS A SPLIT LIFE CYCLE IN WHICH ASEXUAL REPRODUCTION OCCURS IN OAT, WHILE SEXUAL REPRODUCTION CAN OCCUR ON AN ALTERNATE HOST RHAMNUS CATHARTICA (COMMON BUCKTHORN), A LARGE RANGE INVASIVE PLANT SPECIES IN NORTH AMERICA. THE ALTERNATE HOST MAY PLAY AN IMPORTANT ROLE IN THE EPIDEMIOLOGY AND PATHOGENICITY EVOLUTION OF PCA BY ACTING AS A RESERVOIR FOR THE PATHOGEN AND ALLOWING SEXUAL RECOMBINATION, THEREBY INCREASING POPULATION DIVERSITY. HOWEVER, THE CONTRIBUTION OF SEXUAL RECOMBINATION TO PCA DIVERSITY IS UNCLEAR. THIS PROJECT WILL ADDRESS THE CONTRIBUTION OF SEXUAL RECOMBINATION, MIGRATION, AND MUTATION TO GENERATING VIRULENCE DIVERSITY IN PCA. THIS WILL BE ACHIEVED BY COMPARING THREE POPULATIONS: ONE FROM THE NORTHERN U.S., WHERE BUCKTHORN IS PRESENT; ONE FROM THE SOUTHERN U.S. WHERE BUCKTHORN IS ABSENT; AND ONE FROM AUSTRALIA WHERE BUCKTHORN IS ABSENT. IN ADDITION, THE PROJECT WILL ALSO CHARACTERIZE GENES IN PCA THAT ARE UNDER SELECTION IN RESPONSE TO HOST RESISTANCE AND IDENTIFY DNA MARKERS ASSOCIATED WITH VIRULENCE. CURRENT PRACTICES TO PREVENT AND CONTROL OAT CROWN RUST INVOLVE MULTIPLE ROUNDS OF FUNGICIDE TREATMENTS, WHICH COME WITH ENVIRONMENTAL AND ECONOMIC COSTS, AS WELL AS PROBLEMS WITH THEIR EFFICACY AND RISKS TO HUMAN HEALTH. THE LONG-TERM RESEARCH GOAL OF THIS PROJECT IS TO CONTRIBUTE TO THE DEVELOPMENT OF ENVIRONMENTALLY-SAFE MANAGEMENT STRATEGIES THAT RELY ON THE USE OF GENETIC RESISTANCE TO REDUCE OR ELIMINATE CROWN RUST EPIDEMICS. THIS PROJECT IS AT THE LEADING FRONT OF APPLYING POPULATION GENOMICS TO SOLVE QUESTIONS RELEVANT TO PLANT PATHOLOGY. A KEY OUTCOME OF THIS PROJECT IS THE ASSESSMENT OF THE EVOLUTIONARY POTENTIAL OF PCA, WHICH HAS IMPLICATIONS NOT ONLY TO THE BREAKDOWN OF RESISTANCE GENES BUT ALSO TOLERANCE TO FUNGICIDES. UNDERSTANDING THE ROLES OF THESE FACTORS IN GENERATING GENETIC DIVERSITY IN PCA IS INSTRUMENTAL TO MODIFY AGRICULTURAL PRACTICES AND REDUCE YIELD LOSSES DUE TO CROWN RUST EPIDEMICS. THE WORK OUTLINED IN THIS PROJECT WILL ADVANCE THE GENETIC UNDERSTANDING OF VIRULENCE EVOLUTION IN PCA AND PROVIDE IMPORTANT INFORMATION TO SUPPORT DISEASE MANAGEMENT DECISION MAKING, INCLUDING RESISTANCE DEPLOYMENT AND POTENTIAL BUCKTHORN ERADICATION PROGRAMS. BUCKTHORN IS ALSO A PRIMARY HOST FOR APHIDS THAT AFFECT THE PRODUCTION OF SOYBEAN; THEREFORE, EVIDENCE TO SUPPORT THE ERADICATION OF BUCKTHORN WOULD ALSO BENEFIT THE PRODUCTION OF OTHER IMPORTANT CROPS.