Researchers have identified a naturally occurring citrus root bacterium that produces a compound capable of suppressing the bacterium associated with huanglongbing (HLB) disease. This offers a potential new avenue for disease management.
A research study examined whether bacteria living naturally on and within citrus plants could help fight Candidatus Liberibacter asiaticus (CLas), the bacterium associated with HLB.
Using an automated system to isolate and screen citrus-associated bacteria, the team examined approximately 2,000 bacterial isolates collected from citrus leaves and roots. Thirty-five showed strong inhibitory activity against Liberibacter crescens, a closely related bacterium used in laboratory testing because CLas cannot currently be grown in conventional culture.
Researchers focused on a root-associated bacterium, Pseudomonas chlororaphis strain SRAM11. They identified phenazine-1-carboxamide (PCN), a compound produced by the bacterium, as a major contributor to its antimicrobial activity.
In tests using citrus hairy roots infected with CLas, PCN significantly reduced pathogen levels after 72 hours. At the tested concentration, its activity was comparable to that of oxytetracycline, an antibiotic used in HLB management.
For citrus growers, the findings point toward the possibility of developing biological tools that use beneficial microbes or their natural compounds to help suppress HLB. Such approaches could eventually complement existing practices aimed at maintaining tree health and managing the HLB-spreading Asian citrus psyllid.
However, the research remains at an early stage. The tests were conducted in laboratory cultures and excised citrus root tissue, not commercial groves. Researchers say further greenhouse and field trials are needed to determine whether the bacterium can establish itself in citrus trees, reduce HLB symptoms and deliver consistent benefits under commercial growing conditions.
The discovery offers a promising research lead, but it is not yet a treatment growers can apply to control HLB.
An article about the study, titled “A high-throughput pipeline for isolation and screening of the citrus bacteriome identifies Pseudomonas chlororaphis with anti-Candidatus Liberibacter asiaticus activity,” was published Oct. 13 in Applied and Environmental Microbiology. The research team included Christopher Drozd, Kathryn Maebori and M. Caroline Roper with the University of California, Riverside; Carolina Ruiz Rivera, Kiana Callahan and Katherine N. Maloney with Point Loma Nazarene University; and Manikandan Ramasamy and Kranthi Mandadi with Texas A&M University.
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