2011 Annual Report 1a.Objectives (from AD-416) Design a ZC specific realtime PCR diagnosis for reliable detections of ZC-infected potato and potato psyllid. 2. Design and develop multi-locus DNA Simple Sequence Repeat (SSR) DNA markers to genotype and assess genetic diversity of ZC-associated Liberibacter bacteria. 1b.Approach (from AD-416) 1. Clone and sequence ZC Liberibacter pathogen to identify suitable sequencing regions for designing realtime PCR. Validate sensitivity and specificity of detection. 2. Conduct whole genome analyze of ZC Liberibacter draft genome and identify SSR loci for designing SSR primers. 3. Conduct population genetic analysis of ZC-associated Candidatus Liberibacter and assess genetic diversity of the pathogen. 3.Progress Report This Reimbursable Agreement supports Objective 2.A of the parent project. The goal of the project is to develop new molecular markers for identification and assessment of genetic diversity of ‘Candidatus Liberibacter solanacearum’ (CLso), a bacterium associated with potato zebra chip disease. Based on the complete genome sequence of CLso, a marker system, named multilocus simple sequence repeats (SSR), was developed. Sixty CLso strains representing US and Mexico populations were analyzed by SSR. The multilocus SSR marker system effectively genotyped CLso strains within and between populations. Genotypic assignment analysis identified two major lineages of CLso in the U.S. population, but only one lineage type was identified among strains isolated in Mexico. The SSR system was shown to discriminate among closely-related strains.