Huanglongbing Disease Management in Citrus Systems

Huanglongbing (HLB), or citrus greening, is a phloem-restricted bacterial disease that threatens commercial and smallholder citrus production worldwide. The principal causal agent, Candidatus Liberibacter asiaticus, is transmitted by the Asian citrus psyllid (Diaphorina citri), leading to disrupted carbohydrate transport, leaf chlorosis, fruit deformity and ultimate tree decline. Management of HLB combines vector suppression, host resistance and therapeutic treatments. Integrated vector control relies on judicious insecticide rotation, biological control agents and cultural practices to reduce psyllid populations while minimising resistance development. Advances in host resistance include the use of transgenic rootstocks and cultivars engineered to express bactericidal peptides or phage-derived endolysins. Complementary strategies focus on nutritional modulation and foliar applications of antimicrobials to suppress bacterial titre and prolong tree productivity. Recent work highlights the importance of early detection, orchard replant strategies and coordinated area-wide management. Despite progress, durable control demands continued innovation in breeding, vector ecology and targeted therapeutics, as well as an integrated, system-level approach that balances economic, environmental and social considerations.

Research from Nature Portfolio

Recent studies have elucidated a key virulence mechanism of the HLB pathogen through the characterisation of a Sec-delivered effector that directly targets citrus immunity. This effector binds and inhibits papain-like cysteine proteases, which are upregulated during infection and contribute to defence. Field analyses revealed differential accumulation of specific protease isoforms with altered activity in symptomatic trees, and transgenic expression of the effector in citrus confirmed its capacity to suppress protease function. These findings advance understanding of pathogen manipulation of host defences and identify protease inhibition as a target for the development of novel resistance strategies or small-molecule interventions designed to restore immune activity in infected trees.

Huanglongbing Disease Management in Citrus Systems publication trend

The graph below shows the total number of articles in huanglongbing disease management in citrus systems across all publications each year (not limited to Nature Index journals).

Technical terms

Huanglongbing (HLB): A destructive citrus disease caused by phloem-restricted Liberibacter bacteria transmitted by psyllid vectors.

Candidatus Liberibacter asiaticus: The dominant bacterial species associated with HLB, residing in phloem and impairing nutrient transport.

Sec-delivered effector: A bacterial protein secreted via the Sec pathway that manipulates host cell processes to favour infection.

Endolysin: A phage-derived enzyme that degrades bacterial cell walls and can be harnessed to confer resistance in transgenic plants.

Phloem-limited: Describes pathogens or molecules confined to the plant’s phloem tissue, affecting long-distance transport.

References

1. An effector from the Huanglongbing-associated pathogen targets citrus proteases. Nature Communications (2018).
2. An endolysin gene from Candidatus Liberibacter asiaticus confers dual resistance to huanglongbing and citrus canker. Horticulture Research (2023).
3. Effects of Candidatus Liberibacter asiaticus infection on metagenome of Diaphorina citri gut endosymbiont. Scientific Data (2023).
4. Function and molecular mechanism analysis of CaLasSDE460 effector involved in the pathogenesis of “Candidatus Liberibacter asiaticus” in citrus. Molecular Horticulture (2023).