A new study suggests that tackling both the bacterium responsible for huanglongbing (HLB) and the tree’s own response to infection may offer a better path for managing the disease.
A report on the research — “Combating citrus greening disease by simultaneously targeting the pathogen and callose-mediated phloem occlusion” — examines how the disease disrupts the movement of sugars through citrus trees. The paper was posted on bioRxiv, an online preprint server for biological research. The authors of the report are Maryam Khalilzadeh, Chun-Yi Lin, John M. Chater, Amit Levy and Christopher Vincent, all with the University of Florida Institute of Food and Agricultural Sciences Citrus Research and Education Center.
HLB is associated with the bacterium Candidatus Liberibacter asiaticus (CLas). As the disease progresses, the bacterium and the tree’s defense responses contribute to the buildup of callose. Callose is a substance that can block the tiny channels responsible for transporting sugars and other nutrients throughout the plant. This disruption helps explain why infected trees decline, produce smaller fruit and suffer reduced yields even when nutrients and water are available.
The researchers investigated whether combining an antibiotic with a treatment that limits callose buildup could improve sugar movement in HLB-affected trees.
The team conducted two field experiments examining how treatments affected sugar transport and the movement of carbon into developing fruit. Carbon is a building block of the sugars that fuel tree growth and fruit development.
The results showed that the callose inhibitor alone improved sugar transport initially, but the benefit did not last. Antibiotic treatment helped developing fruit receive more carbon, although results across different measurements were mixed.
The strongest results came from combining the two treatments. The researchers reported less callose buildup, improved transport through the phloem — the plant tissue that carries sugars — and better allocation of carbon to fruit when demand was high. Treated trees also experienced less fruit drop and accumulated more carbon in fruit following the natural fruit-drop period.
The findings highlight an important point: Managing HLB may require addressing both the bacterium and the damage that develops inside the tree. Simply reducing bacterial pressure or temporarily improving sugar transport may not be enough to deliver lasting benefits.
For Florida growers struggling with premature fruit drop and declining productivity, this combined approach could help guide future treatment development. However, the findings do not establish a commercially proven solution, and the reported improvements in carbon movement should not be interpreted as confirmed increases in marketable yield or profitability.
The study is an early research report, not a recommendation to apply unapproved treatments. Additional research is needed to establish long-term yield effects, treatment safety, application methods and economic feasibility under commercial growing conditions.
Read the full report on the research here.
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