Huanglongbing (HLB) is a critical concern for the global citrus industry, posing significant socioeconomic challenges. This bacterial disease, caused by the genus Candidatus Liberibacter, infects the phloem of citrus trees, leading to the obstruction of nutrient transport vessels. The disease is primarily spread by psyllid insects, which transmit the bacteria while feeding on citrus shoots. Despite the universal susceptibility of popular citrus species such as oranges, mandarins, grapefruits, and lemons, certain genotypes exhibit varying degrees of tolerance or resistance. Over recent decades, substantial efforts have been directed towards identifying these resilient genotypes. However, progress in understanding the physiological and molecular bases of this tolerance or resistance has been limited. Key gaps remain in identifying the specific genes involved and elucidating the comprehensive physiological responses at the whole-tree level. Addressing these gaps is crucial for developing molecular tools to enhance resistance in both the vector and the citrus trees themselves. Additionally, a deeper understanding of host-pathogen-vector interactions is essential for devising new disease management strategies.

This research topic aims to explore the molecular and physiological mechanisms underlying tolerance and resistance traits in citrus concerning HLB, as well as the interactions between the host, pathogen, and vector. The primary objectives include identifying the genes responsible for resistance, understanding the physiological responses at the whole-tree level, and characterizing the transmission mechanisms of the disease. By addressing these questions, the research seeks to pave the way for innovative molecular tools and strategies to manage HLB more effectively.

To gather further insights into the boundaries of this research, we welcome articles addressing, but not limited to, the following themes:

- Genetics and breeding to identify tolerance/resistance genes to HLB (bacterium/vector)
- Physiological approaches to decipher resistance/tolerance mechanisms in citrus to HLB (bacterium/vector)
- Whole plant response to HLB (bacterium/vector), including impact at the fruit level
- Molecular tools to confer HLB resistance in citrus/vector
- Host-pathogen-vector interaction and transmission mechanisms
- New methods in HLB disease diagnosis

We encourage submissions in various formats, including original research, reviews, mini-reviews, commentary, protocols, opinions, and perspectives.

Disclaimer: We acknowledge that Drs. Morillon and Hufnagel receive funding from Cointreau, Campari and Suntory for scientific research activities. But, we hereby state publicly that Cointreau, Campari and Suntory has had no editorial input in articles included in this Research Topic, thus ensuring that all aspects of this Research Topic are evaluated objectively, and unbiased by any specific policy or opinion of Cointreau, Campari and Suntory. The other Topic Editors declare no competing interests with regard to the Research Topic subject.

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Unraveling Molecular Mechanisms of Citrus Resistance to Huanglongbing