The purpose of this project is to reveal the mechanisms of bactericide uptake and transport in citrus plant and establish a theoretical basis for developing technologies to improve the efficacy of bactericides, which is helpful to provide potential solution to the development of effective chemotherapeutic tools for HLB management. Achieving this outcome will require progress in the following three tasks: (1) to compare the delivery efficacy of bactericides with three application methods (foliar spraying, truck injection, and root administration) based on the uptake and dynamic movement/distribution of the bactericide within the tree; (2) to clarify the systemic movement and transportation mechanisms of bactericides within the phloem of tree; and (3) to investigate the effects of citrus variety and age on the delivery efficacy of bactericides. This project requires a combination of greenhouse studies and field trials. Prior to conducting these experiments, a sensitive and accurate quantifying method of bactericides (oxytetracycline and streptomycin) in citrus tissues is needed. This project officially started on December 1, 2019. This is the first quarterly progress report covering 12/01 to 02/29, 2019. During this period we have started and/or completed the following work/research tasks: 1. A project team meeting was held to plan this year’s research activities and define the responsibilities of PI, Co-PI, participants, and collaboration partners. 2. A work plan with detailed information on experimental design, measurements and analytical methods was developed and will be followed by all the participants. 3. Preparation for project research, including purchase of chemicals, labware and small equipment was completed. 4. Samples of citrus leaf, stem, and fruit were collected from fields. These samples were treated with antibiotics to be studied and used for testing and validating existing methods for detecting trace amounts of antibiotics in plant tissues and fruit. The work planned for the next quarter: The major goal of research for the first six months are to develop an improved robust analytical method for detecting and quantifying antibiotic concentration in citrus samples. The following research will be conducted in the 2nd quarter to accomplish this goal. 1. Laboratory experiments and analyses to test existing methods for detecting antibiotics in citrus plant tissues and fruit samples. 2. Continue to collect plant tissue and fruit samples from citrus fields where oxytetracycline and/or streptomycin were frequently applied. 3. Laboratory experiments and analyses to improve antibiotic extraction and cleanup procedure based on the results from preliminary experiments. 4. Laboratory experiments and analyses to establish a reliable methods for extraction and analyzing antibiotics in citrus samples using LC-MS/MS. 5. To culture citrus plants according to the work plan for the greenhouse experiments.