2012 Annual Report 1a.Objectives (from AD-416): 1. Perform genome-wide sequence analysis to identify Simple Sequence Repeat (SSR) loci. 2. Genotyping and phenotyping of CLas strains, characterizing virulent strains, host pathogen interactions; adaptation, selection and strain – strain competition. 3. Analyzing CLas population structures, assessing genetic diversity of CLas in Florida populations. 1b.Approach (from AD-416): 1. Complete genome gaps from current draft genome using long distance PCR and genomic walking techniques. 2. PCR and fragment analyses of asiaticus isolates collected from Florida populations. 3. Conduct molecular variance analysis to assess hierarchical structures of pathogen population in Florida. Documents Trust with Florida Citrus Production Research Advisory Council. Log 43636. 3.Progress Report: Results from this study are in support of Objective 1 of the parent project. The overall goal of the project is to investigate genetic diversity and structure of global populations of “Candidatus Liberibacter asiaticus’ (Las) strains. Results from this study identified three major genetic groups of Las worldwide. Isolates from Brazil showed similar genetic makeup with east-southeast Asian dominant group, suggesting the possibility of a common origin. Most of the isolates detected from Florida were clustered in a separate group. While source of the dominant Las in Florida was not clearly identified, the less-pervasive groups appear to be closely related to isolates from Asia and Brazil. Notably, the recent outbreak of Huanglongbing (HLB) in Florida probably occurred through multiple introductions from at least two sources. Microsatellite markers developed in this study provide adequate discriminatory power for detection, strain differentiation and population genetic analyses of ‘Ca. L. asiaticus’.