The long-term goals of this predoctoral fellowship project are as follows:1. Determine the origins of the plant pathogen, Candidatus Liberibacter solanacearum (CLso), in the southwestern region of the United States (research goal).2. Understand genetic drivers of host-associated differentiation in the tomato-potato psyllid (Bactericera cockerelli), which transmits CLso and is a major pest of solanaceous crops (research goal).3. Obtain a PhD in Entomology along with skills/expertise required to build a career as an agricultural scientist and educator within academia or government (training/mentoring goal).The research goals of this project will address fundamental unknowns in the ecology and emergence of pathogens in the genus Candidatus Liberibacter, which are increasingly emerging as important insect-transmitted crop pathogens worldwide. On average, one new pathogen in this genus has been discovered each year following the appearance of a disease condition in crops. This will likely continue as climate change and global trade drive new contacts between pathogens, vectors, and crops. By understanding the pathways to CLso emergence as a crop pathogen, this project will provide resources to mitigate situations that facilitate emergence of CLso in new areas, new CLso variants, and related pathogens in the genus Candidatus Liberibacter. Likewise, clarifying the population structure and host associations of different vector haplotypes will determine if vector behavior and preferences are playing a key role as drivers of CLso movement and adaptation to crop hosts. Finally, undertaking this project will provide necessary training in project management to prepare the PD for the next career stage. To accomplish the proposed research goals, the PD will complete two objectives:1: Perform reciprocal inoculation assays to quantify the host range and pathological effects of wild plant-associated CLso G on crop hosts, and crop-associated CLso B on a wild host.2: Determine the population structure of potato psyllids in the southwestern US by combining community-based sampling and high-throughput genotyping-by-sequencing.