Trunk-Injected Antibiotic Reshapes Citrus Leaf Microbiome and Helps Trees Recover from Devastating Greening Disease

Huanglongbing, also known as citrus greening, remains the most destructive disease facing citrus production worldwide, and a new study from Texas A&M University researchers offers fresh insight into why one of the few available treatments appears to work. Published in BMC Plant Biology, the research shows that trunk-injected oxytetracycline does more than directly suppress the bacterium behind the disease. According to the study, the antibiotic also reshapes the community of bacteria living inside citrus leaves, temporarily reducing and then enriching groups of microbes that appear to help trees fight back against infection.

The research team, led by Chuanyu Yang and Veronica Ancona at the Citrus Center of Texas A&M University-Kingsville in Weslaco, together with Kranthi Mandadi of Texas A&M AgriLife Research, set out to address a gap in the understanding of how antibiotic therapy affects citrus beyond its direct antimicrobial action. Oxytetracycline trunk injection has already shown promise in reducing disease severity and improving tree health and productivity in affected groves, but the researchers hypothesized that part of its benefit might come from changes to the endophytic microbiome, the community of microorganisms that live within plant tissues without causing harm.

To test this idea, the team worked with Huanglongbing-affected grapefruit trees in a field setting. Some trees received a trunk injection of oxytetracycline at a concentration of 50,000 parts per million, while control trees were injected with water. The researchers then tracked changes in the leaf endophytic microbiome at three time points: immediately before injection, fifteen days after treatment, and forty-five days after treatment. They used 16S rDNA amplicon sequencing, a technique that reads a specific region of bacterial ribosomal DNA to identify and quantify the bacterial taxa present in each sample, giving a detailed census of the microbial community inside the leaves.

Alongside the microbiome analysis, the team measured titers of Candidatus Liberibacter asiaticus, the phloem-limited bacterium responsible for Huanglongbing, as well as a suite of agronomic traits reflecting tree health and field performance. This dual approach allowed the researchers to connect shifts in the microbial community with both pathogen burden and the physical condition of the trees over the six-week observation window.

The results confirmed that trunk injection of oxytetracycline reduced the titers of the HLB-associated pathogen, improved the field performance of treated trees, and significantly altered the composition of the leaf endophytic microbiome. But the most intriguing finding concerned the timing of microbial change. Fifteen days after treatment, the researchers observed a reduction in potentially beneficial bacteria within the leaf community. By forty-five days after injection, however, those same beneficial groups had become enriched, rebounding to higher relative abundance than before.

This temporal pattern suggests a two-phase effect. In the immediate aftermath of injection, the antibiotic appears to act broadly, suppressing susceptible bacteria including some that may be helpful to the tree. As the compound dissipates or the community reorganizes, beneficial taxa recover and expand, potentially filling ecological space vacated by the pathogen and other competitors. The researchers propose that this delayed enrichment of beneficial bacteria may be involved in the observed improvement in field performance, providing a microbiome-mediated contribution to tree recovery that extends beyond the antibiotic’s direct effect on the pathogen.

Correlation analysis strengthened this interpretation. Using Spearman correlation, the team found a significantly negative relationship between the relative abundance of two bacterial genera, Sphingomonas and Aermicrobium, and the titer of Candidatus Liberibacter asiaticus. In other words, when these genera were more abundant, the pathogen was less so. This pattern positions both genera as potential antagonists of the HLB bacterium, organisms that may compete with or actively suppress it within the leaf environment.

Sphingomonas in particular has drawn attention in plant microbiome research as a genus frequently associated with disease suppression across a range of crops. Its members are known for versatile metabolic capabilities and for colonizing plant surfaces and internal tissues. The new findings suggest that within citrus leaves, this genus and the less-studied Aermicrobium may represent natural allies whose abundance could be deliberately encouraged as part of an integrated disease management strategy.

The implications reach beyond the immediate question of antibiotic treatment. If the health benefits of oxytetracycline injection depend partly on fostering beneficial endophytes, then future approaches might aim to amplify that effect directly, for example by introducing or supporting specific bacterial strains after treatment. The study provides what the authors describe as valuable information about the interactions between the pathogen and the leaf microbiome that can be explored for developing new strategies to suppress citrus Huanglongbing, a disease for which no cure currently exists and which has devastated groves in Florida, Texas, and other production regions around the world.

The work was supported by funding from the United States Department of Agriculture’s National Institute of Food and Agriculture, Texas A&M AgriLife Research, and related internal grant programs. As Huanglongbing continues to spread and threaten citrus industries globally, understanding the microbial dimension of tree health may prove as important as targeting the pathogen itself, and this study offers one of the clearest pictures yet of how a therapeutic intervention ripples through the invisible ecosystem inside a citrus leaf.

Subject of Research: Effects of trunk-injected oxytetracycline on the leaf endophytic microbiome and health of Huanglongbing-affected citrus trees

Article Title: Trunk-injected oxytetracycline alters the leaf endophytic microbiome and promotes health recovery in Huanglongbing-affected citrus

Article References: Yang, C., Pasupuleti, L. A., Mendez, R., Kolla, T. C., Mandadi, K., & Ancona, V. (2026). Trunk-injected oxytetracycline alters the leaf endophytic microbiome and promotes health recovery in Huanglongbing-affected citrus. BMC Plant Biology. https://doi.org/10.1186/s12870-026-10179-4

Image Credits: AI Generated

DOI: 10.1186/s12870-026-10179-4

Keywords: Huanglongbing, citrus greening, oxytetracycline, endophytic microbiome, Candidatus Liberibacter asiaticus, Sphingomonas, Aermicrobium, trunk injection, citrus health, 16S rDNA sequencing, plant microbiome, BMC Plant Biology