Objective 1. Identify key metabolites that are associated with rootstock traits. Summary of accomplishments: Metabolite profiles of greenhouse-grown rootstock seedlings of eleven rootstock cultivars (Cleopatra, Swingle, Sour orange, Ridge Pineapple, Carrizo, US-802, US-812, US-896, US-897, US-942, US-1516) with known horticultural traits were assessed for primary metabolites possibly associated with traits. Analysis has been completed on a preliminary dataset. The data from an additional study to corroborate findings were recently received from West Coast Metabolomics Center (WCMC), UC-Davis, and are being used for detailed analysis by the USDA-IFAS team. Additional supporting studies are being conducted, including physiological assays and confirmation of identified compounds using chemical standards. The team is currently working on establishing these procedures to strengthen research findings. Objective 2. Investigate the effect of grafting on metabolite profiles. Summary of accomplishments: The four standard rootstocks (Cleopatra, Swingle, Ridge, and Sour orange) and seven additional rootstocks (Carrizo, US-802, US-812, US-896, US-897, US-942, US-1516) were analyzed as greenhouse-grown grafted trees in combination with Valencia. Metabolic profiles of leaves and roots of the grafted trees are being compared with those of leaves and roots from rootstock seedlings to assess rootstock effects on the scion and the possible implications for tree performance. Extensive additional metabolic data from our experiments were received back from the West Coast Metabolomics Center (WCMC), UC-Davis, and are being used for detailed analysis by the USDA-IFAS team. Due to the complicated nature of these data sets, this process is expected to take several months until ready for publication. In addition to the study of greenhouse-grown trees, analysis of metabolite profiles has been expanded to grafted trees grown under field conditions. A current data set including young trees with two different scion cultivars (Cara Cara and Hirado) in combination with the eleven rootstocks is in final process of analysis. A publication is expected to be submitted in the next few months. These studies will aid in identifying rootstock-scion interactions and the possible impacts on stress and disease tolerance under commercial conditions. Objective 3. Establish metabolite profiles of trees on different rootstocks in response to HLB. Summary of accomplishments: An experiment consisting of 300 grafted trees grown in the USDA greenhouses was completed. Trees were composed of Valencia grafted on a diverse array of standard and USDA rootstock cultivars and were either mock-inoculated or inoculated with Las. PCR analysis of Las bacterial titers of leaves and roots for the trees at different time intervals is in process. Leaf and root tissue of Las-infected and Las-uninfected plants were collected at 30 weeks after inoculation, and appropriate extractions completed. Samples from these experiments were sent to WCMS for GC-TOF-MS analysis of primary metabolites in April 2017, and the resulting metabolic data were recently received. A second set of samples from the experiment was recently sent to WCMS for analysis of secondary metabolites. Results from these analyses will be used by our USDA-IFAS team to conduct detailed analysis of metabolite profiles associated with HLB response. Publication of the results in a refereed journal will be completed, along with identification of practical utility of the information. Experimental design, data collected, analysis, results, and interpretation are too complex to present here. Additional information is available on request.