Recent Progress in the Understanding of Citrus Huanglongbing: From the Perspective of Pathogen and Citrus Host

Abstract

Citrus Huanglongbing (HLB), or citrus greening disease, caused by the phloem-restricted bacterium Candidatus Liberibacter asiaticus (CLas) and transmitted primarily by the Asian citrus psyllid (Diaphorina citri), remains one of the most devastating threats to global citrus production, with no definitive cure. This review synthesizes recent advancements in understanding HLB from dual perspectives: the pathogen, focusing on genomics, effectors, virulence factors, transmission dynamics, and detection methods; and the citrus host, emphasizing perception and signaling, metabolic disruptions (starch accumulation, callose deposition, and source-sink imbalances), defense responses, and tolerance mechanisms in resistant varieties and relatives. Integrated insights highlight pathogen-host interactions, including effector-mediated suppression of plant immunity and multi-omics approaches like dual RNA-seq for elucidating molecular dialogues. Management strategies encompass vector control, sanitation, breeding for resistance via CRISPR genome editing, RNA interference, antimicrobial peptides, microbiome engineering, and nutritional therapies. Challenges such as CLas uncultivability and knowledge gaps in functional genetics are discussed, alongside future directions for early detection innovations, sustainable interventions, and multi-omics breeding pipelines to enhance citrus resilience.

Keywords: Candidatus Liberibacter, CRISPR, Citrus Huanglongbing, IPM, RNAi-Based Control