BACTERIAL PLANT PATHOGENS RESULT IN CROP DEATH AND LOSS OF ARABLE LAND. RALSTONIA SOLANACEARUM, WHICH CAUSES BACTERIAL WILT IN A WIDE RANGE OF ECONOMICALLY AND NUTRITIONALLY RELEVANT CROPS, IS ENDEMIC IN TOMATO GROWING REGIONS OF THE SOUTHEASTERN US. THE PATHOGEN PERSISTS IN WATER AND SOIL IN THE ABSENCE OF A HOST, LIMITING FUTURE PRODUCTION IN INFESTED SOIL. FURTHER, THIS PATHOGEN CAN BE CARRIED ASYMPTOMATICALLY IN ORNAMENTAL PLANTS THAT ARE IMPORTED COMMERCIALLY, REPRESENTING A THREAT FOR THE INTRODUCTION OF SELECT AGENT STRAINS OF THIS PATHOGEN INTO THE US. DUE TO THE EXTRAORDINARY GENETIC DIVERSITY WITHIN THE RALSTONIA SOLANACEARUM SPECIES, DEVELOPING UNIVERSALLY RESISTANT PLANT LINES IS CHALLENGING; HOWEVER, BASIC RESEARCH ON PATHOGEN-HOST INTERACTION HAS THE POTENTIAL TO LEAD TO EFFECTIVE PATHOGEN MANAGEMENT STRATEGIES THAT LIMIT DISEASE OUTBREAKS. MANY MOTILE SOIL-DWELLING BACTERIA, INCLUDING RALSTONIA SOLANACEARUM, USE A SWIMMING BEHAVIOR CALLED CHEMOTAXIS TO MOVE TOWARD SPECIFIC ATTRACTANT CHEMICALS AND AWAY FROM REPELLENT CHEMICALS. CHEMICALS EXUDED FROM PLANT ROOTS FUNCTION AS ATTRACTANTS THAT ARE SPECIFICALLY SENSED BY BACTERIA, ALLOWING THEM TO FIND AND COLONIZE ROOTS IN THE SOIL. SPECIFIC BACTERIAL PATHOGENS THUS INITIATE INFECTIONS BY SENSING AND PREFERENTIALLY MOVING TOWARDS THE ROOTS OF HOST PLANTS OVER THOSE OF NONHOST PLANTS. IMPORTANTLY, MUTANTS OF RALSTONIA SOLANACEARUM THAT ARE NOT CHEMOTACTIC HAVE BEEN SHOWN TO BE UNABLE TO COLONIZE HOST PLANTS FROM THE SOIL, MAKING CHEMOTAXIS AN INTERESTING TARGET FOR PATHOGEN CONTROL.CHEMOTAXIS IS MEDIATED BY DOZENS OF PROTEIN RECEPTORS ON THE BACTERIAL CELL SURFACE THAT EACH RECOGNIZE A UNIQUE SUITE OF CHEMICAL ATTRACTANTS. USING INNOVATIVE GENETIC TECHNIQUES, WE AIM TO IDENTIFY RECEPTORS AND CHEMICAL SIGNALS SENSED BY RALSTONIA SOLANACEARUM THAT ALLOW THEM TO LOCATE AND INFECT HOST ROOTS (E.G., TOMATO, MELON, AND NEW GUINEA IMPATIENS). IN THIS STUDY, WE WILL COMPARE THE CHEMOTAXIS OF TWO STRAINS, ONE WITH A BROAD HOST RANGE (KNOWN TO INFECT TOMATO, MELON AND NEW GUINEA IMPATIENS) AND ONE WITH A NARROW HOST RANGE (KNOWN TO INFECT ONLY TOMATO). WE EXPECT TO IDENTIFY RECEPTORS THAT RECOGNIZE BOTH COMMON PLANT ROOT EXUDATES AND HOST SPECIFIC SIGNALS. FURTHER, WE AIM TO IDENTIFY THE ROLE THAT THESE RECEPTORS PLAY IN THE PATHOGENIC FITNESS OF RALSTONIA SOLANACEARUM AND HOW DISRUPTION OF THESE RECEPTORS AFFECTS THE ABILITY OF THE BACTERIA TO INFECT PLANTS. IN THE LONG TERM, THIS RESEARCH WILL GENERATE TARGETS AND METHODS FOR BIOLOGICAL AND CHEMICAL CONTROL OF THIS ECONOMICALLY DEVASTATING PATHOGEN, WHICH WILL PROTECT CROPS FROM INFECTION AND POTENTIALLY RESTORE INFECTED SOIL.