Modeling huanglongbing transmission within a citrus tree

Area of Science:

• Plant pathology
• Epidemiology
• Mathematical modeling

Background:

• Huanglongbing (HLB) is a devastating citrus disease caused by an uncultured bacterium.
• HLB poses a significant threat to the global citrus industry.
• Current models often treat the entire plant as the unit of analysis for vector-transmitted diseases.

Purpose of the Study:

• To develop a mathematical model simulating HLB transmission dynamics within citrus trees.
• To analyze the roles of vector activity, flush-to-flush spread, and host factors in HLB epidemics.
• To evaluate the impact of control strategies like psyllid spraying and symptomatic flush removal.

Main Methods:

• Developed a novel mathematical model focusing on pathogen spread between flushes within a citrus tree.
• Simulated realistic dynamics of vector and host populations during disease progression.
• Analyzed model parameters influencing HLB development and the efficacy of control interventions.

Main Results:

• Vector activity is crucial for initial HLB infection, but not for sustained spread within the tree.
• Internal, flush-to-flush pathogen movement is a significant driver of HLB epidemics.
• Flush production, within-tree spread dynamics, and latent period are key factors in HLB development.
• Control strategy effectiveness (psyllid spraying, flush removal) is highly dependent on timing, frequency, and efficacy.

Conclusions:

• Within-tree spread and resistance mechanisms are critical factors in HLB epidemic development.
• Non-vector-mediated transmission routes can be important for HLB spread.
• The model provides insights into HLB dynamics and informs targeted disease management strategies.