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, and a reliable and accurate method for quantifying bactericides (oxytetracycline and streptomycin) in citrus tissues. This project officially started on December 1, 2018. This is the 3rd quarterly progress report covering 6/01 to 08/31, 2019. During this period we have started and/or completed the following work/research tasks:
1) The extraction method for oxytetracycline and streptomycin in citrus samples was further improved. Now we have a simpler and faster extraction method with a small SPE cartridge (Waters Oasis HLB 1 cc, 30 mg) to replace the previously used big one (Waters Oasis HLB 6 cc, 500 mg). Besides, the newly developed method was validated in terms of specificity, linearity, precision, accuracy and recovery with reference to the guideline established by the International Conference on Harmonization of Technical Requirements for Registration of Pharmaceuticals for Human Use Validation of analytical procedures.
2) We finished the planned citrus foliar spraying experiment. Plant samples (leaves, branches, and roots) were collected from the treated citrus trees at 0 (control), 7, 15 and 30 days after treatment. The samples were extracted and analyzed for bactericides using the above newly developed method. Preliminary results showed that both oxytetracycline and streptomycin could be detected in all the plant samples even at day 30 after spraying except for streptomycin in root. More biological replicates will be analyzed to verify the results.
3) For the trunk injection experiment, work was performed to develop some specific apparatus for trunk injection, and some trial tests were conducted to optimize flow speed of bactericide solution and ensure steady absorption of antibiotics into citrus trees under field conditions.
The work planned for the next quarter:
The major goals of research for the next three months are to obtain the final results of foliar spraying experiment and evaluate the delivery efficacy of bactericides within citrus trees based on the three different application methods (foliage spraying, trunk injection, and root administration). The following research tasks will be conducted in the 4th quarter: 1) More biological replicates of plant samples from the foliar spraying experiment will be analyzed to verify the present result; 2) The planned trunk injection experiment will be conducted; 3) Prepare for root administration of bactericide experiment.