IN THE LAST 10 YEARS, THE POTATO PSYLLID, BACTERICERA COCKERELLI, HAS BECOME A SERIOUS PEST OF SOLANACEOUS CROPS. POTATO PSYLLIDS TRANSMIT "CANDIDATUS LIBERIBACTER SOLANACEARUM" (LSO), THE CAUSATIVE AGENTS OF POTATO ZEBRA CHIP (ZC), A PLANT DISEASE RESPONSIBLE FOR MILLIONS OF DOLLARS IN LOSSES TO THE POTATO INDUSTRY. RECENTLY, THE EXISTENCE OF TWO LSO HAPLOTYPES IN THE USA WAS DISCOVERED. THE GEOGRAPHIC DISTRIBUTION OF LSO HAPLOTYPES AND THEIR PATHOGENICITY MIGHT EXPLAIN INCONSISTENCIES REPORTED BY SCIENTISTS RELATED TO DISEASE DEVELOPMENT AND SEVERITY, AND THE OUTCOME OF INFECTED PLANTS. UNDERSTANDING THE GEOGRAPHIC DISTRIBUTION OF EACH HAPLOTYPE AS WELL AS DIFFERENCES IN THE PATHOLOGY THEY CAUSE TO POTATOES WILL IMPROVE OUR UNDERSTANDING OF ZC EPIDEMIOLOGY BUT IT ALSO HAS THE POTENTIAL TO AFFECT POTATO CERTIFICATION PROGRAMS. WE PROPOSE TO EXAMINE THE GEOGRAPHICAL DISTRIBUTION OF LSO HAPLOTYPES IN THE USA AND MEXICO AND ASSESS DISEASE AND SYMPTOM DEVELOPMENT ASSOCIATED WITH EACH LSOHAPLOTYPE. ALSO, WE WILL IDENTIFY BACTERIAL GENES INVOLVED IN PATHOGENICITY INCLUDING PROTEIN EFFECTORS, AND WE WILL EVALUATE PLANT RESPONSES TO INFECTION BY EACH HAPLOTYPE.AT THE END OF THIS STUDY WE WILL HAVE A BETTER UNDERSTANDING OF ZC DISEASE AND GENES INVOLVED IN LIBERIBACTER PATHOGENICITY. EMPHASIS WILL BE PLACED IN STUDENT TRAINING IN MOLECULAR TECHNIQUES AND TRANSFER OF INFORMATION OBTAINED IN THIS PROJECT TO END-USERS.