New research from UF/IFAS shows the citrus trees and HLB have a complex relationship that makes finding a cure difficult.

Researchers have been trying to find a cure or treatment for HLB, also called citrus greening, since the disease was discovered in Florida in 2005. According to a UF/IFAS blog about new research concerning the complex relationships between citrus trees and HLB, researchers have their work cut out for them. Explore the details below.

The Relationship Between Citrus Trees and HLB

According to the article, the research uncovered “new ways that the bacteria interact with a citrus tree’s natural defenses.” This information will hopefully help researchers to devise a cure or treatment.

When the HLB-causing bacteria—CLas—infect a citrus tree, the tree creates a material called callose, which acts as a plug in the tree’s phloem. This in turn generates “reactive oxygen species” or ROS. The article maintains that “ROS is involved in a plant’s defense systems and impacts a plant’s tolerance to various types of stress.  Presence of a pathogen like CLas can increase ROS production to a negative effect and eventually cause cell death.”

The research showed that the CLas bacteria can actively reduce the callose and ROS, which allows the bacteria to continue to replicate and move all throughout the tree. This creates a “back-and-forth repetitive relationship of callose plugging and reactive oxygen species accumulation—and then their elimination by Clas…” The article maintains that “Citrus varieties that maintain a fine balance between callose and reactive oxygen species generation and then elimination without either side gaining “control” may be more inclined to continue to produce fruit over many years.”

UF/IFAS assistant professor of plant pathology and one of the authors of the research, Amit Levy, said in the article, “This research demonstrates the complicated, intertwined relationship between the HLB bacteria and the tree’s immune defense system. The fact that CLas developed mechanisms to suppress the immunity tells us that the plant immunity is critical to stop the bacteria. The HLB disease is about both the pathogen and the immune response, and their interaction. It is a fine balance.”

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