Mike Roberts

Is Latest Research a Greening Game-Changer?

The Florida citrus industry could use a “game-changer” in the fight against citrus greening, and they may get it with the research being done by UF/IFAS Professor of Microbiology and Cell Science, Nian Wang. Wang’s latest research suggests that citrus greening is a pathogen-triggered immune disease, which could bring about new possibilities in managing the disease.

What is a Pathogen-Triggered Immune Disease? 

pathogen-triggered immune disease is when a pathogen like a virus, bacteria, or parasite invades an organism and causes an immune response that damages that organism. While not yet seen in the plant world, pathogen-triggered immune diseases are common in humans, such as when an infection causes a person’s fever to go so high that it causes brain damage or organ failure. Essentially, the citrus greening symptoms that debilitate a citrus tree are caused by the tree’s own immune response to the infection.


Citrus Greening as a Pathogen-Triggered Immune Disease


When the Candidatus Liberibacter asiaticus (CLas) bacteria that cause citrus greening enter a citrus tree’s phloem tissue, the infection stimulates systemic and chronic immune responses. These responses include the overproduction of reactive oxygen species (ROS). This “chronic and excessive ROS production” causes systemic cell death of phloem tissues, which in turn shows up as the symptoms of citrus greening that cause declining tree health, loss of fruit production, and eventual tree death.


Wang’s research included testing growth hormones that counteract the effects of ROS, namely gibberellin acid and the antioxidant uric acid, to prove the pathogen-triggered immune disease hypothesis. Both of these growth hormones halted or reduced cell death, showing that citrus greening is possibly a pathogen-triggered immune disease.


Wang’s research also identified the RBOHD gene that is responsible for producing ROS in response to CLas infection in citrus trees. Researchers could utilize this information to edit the gene using CRISPR technology, silence genes like RBOHD that lead to ROS production and cell death, and more.


Wang maintained that the new research could lead to new options for combating citrus greening and mitigating ROS, such as: 

  • Integrated horticultural measures, such as GA and using optimized fertilization and micronutrients.
  • Genetic improvements of citrus varieties with antioxidant enzymes.
  • Generating non-transgenic HLB resistant/tolerant citrus varieties by editing key genes required for CLas-triggered ROS production
  • Using CTV-mediated expression of antioxidant enzymes and silencing of key genes required for CLas-triggered ROS production

This column is sponsored by Griffin Fertilizer Co., and the opinions expressed herein may not reflect those of CFAN or of its advertisers.  

BIO: Mike Roberts is the Vice President of the Frostproof, Fla.-based Griffin Fertilizer Co. Roberts joined the company in November 2011. He has spent the majority of his career in the fertilizer/agchem industry. Roberts earned a Bachelor of Science degree in citrus production from Florida Southern College in Lakeland. For more information, visit griffinfertilizer.com.


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