Potential Rotational or Alternative Partners of Oxytetracycline for Huanglongbing Management
Posted August 2025
Researchers: Ozgur Batuman, Lauren Fessler Mathews, Sanju Kunwar, Ana Redondo
Contact: Ozgur Batuman, UF/IFAS SWFREC obatuman@ufl.edu
Summary:
The antibiotic oxytetracycline (OTC) can suppress the population buildup of Candidatus Liberibacter asiaticus (CLas) in huanglongbing (HLB)-affected trees through trunk injection. Florida citrus growers have been utilizing this technique since 2022; however, scientists anticipate OTC resistance development in CLas populations. Such resistance development may be slowed by rotating OTC with a different antibiotic, ideally with different modes of action. Instead of injecting citrus trees with only OTC each year, we are investigating trunk injections with OTC in the spring, after the spring flush is fully expanded (April-May 2024), and then subsequently in the fall (September-October 2024) in the same trees with a different antibiotic. This antibiotic rotation method would help to control CLas in HLB-affected trees, extend the efficacy of OTC for citrus growers as long as financially possible, and slow down OTC resistance development in CLas bacteria. The overall goal of this project is to determine whether or not OTC, rotated with another antimicrobial, has an equal or better effect on CLas titers than injecting OTC alone in HLB-affected citrus trees without causing phytotoxicity. Therefore, we will utilize sequential trunk injections of 5 different antibiotics. We also want to monitor the phytotoxicity for each antibiotic rotation regimen to ensure growers will use the safest products/concentrations for their trees. By finding antibiotics that can serve as rotational partners to OTC, we can help slow down OTC resistance development in CLas bacteria and extend the financial benefits of OTC-trunk injections until a more long-term HLB solution is developed.
Take Home Message:
- OTC injections currently suppress CLas, but resistance may occur within a few years.
- Trunk injections of different antibiotics have the potential to control CLas but need to be assessed for phytotoxicity.
- OTC resistance development could be slowed by rotating trunk injections with different antibiotics.
