Agriculture

The complex relationship of citrus greening bacteria with the tree’s defense system

citrus greens…

Creates ongoing challenges for scientists, suggests a new UF/IFAS paper

Huanglongbing, or HLB, also known as citrus greening, has been wreaking havoc on Florida citrus groves for over 15 years. Researchers at the University of Florida’s Institute of Food and Agricultural Sciences (UF/IFAS) are continuing to study the bacteria that causes the deadly disease, learning more about how it affects citrus trees – all in an effort to find viable solutions for growers. (Photo by UF/IFAS)

LAKE ALFRED, Fla. — At the heart of a disease threatening Florida’s citrus industry is a complex exchange between the citrus tree and a sneaky bacterium.

Huanglongbing, or HLB, also known as citrus greening, has been wreaking havoc on Florida citrus groves for over 15 years. Researchers at the University of Florida’s Institute of Food and Agricultural Sciences (UF/IFAS) are continuing to study the bacteria that causes the deadly disease, learning more about how it affects citrus trees – all in an effort to find viable solutions for growers.

In the new work, Amit Levy, assistant professor of plant pathology, and first author Chiara Bernardini, a postdoctoral fellow in Levy’s lab, discovered several new ways bacteria interact with citrus trees’ natural defenses. Their findings shed light on the complexity of the disease’s path within the tree and what that means for scientists looking to mitigate its deadly impact.

Levy and Bernardini discovered how bacteria and citrus enter into a reaction relationship “back and forth”. He and others showed that after infection with SLas (Candidate Liberibacter asiaticus) bacteria, the tree’s defense system begins to produce callose in the phloem, a material that essentially “clogs” the phloem and creates so-called “reactive oxygen species” or ROS.

In plants, ROS participates in the protective systems of plants and affects the resistance of plants to various types of stress. The presence of the causative agent, as SLas can increase the production of ROS to a negative effect and eventually cause cell death.

Levy’s research showed that SLas bacteria responded to the generation of callose and reactive oxygen species by actually reducing them, allowing the bacteria to reproduce and transport through the wood again.

This recurring relationship of callous plugging and accumulation of reactive oxygen species and their subsequent elimination by SLas is complex and replicates the host-pathogen immune response competition found in many other diseases.

Citrus cultivars that maintain a delicate balance between generating callose and reactive oxygen species and then eliminating them without gaining “control” on either side may be more likely to continue fruiting for many years.

“This study demonstrates a complex relationship between HLB bacteria and the tree’s immune defense system.” – said Levi. “The point is that SLas-evolved mechanisms for suppressing immunity tell us that plant immunity is crucial for stopping bacteria. HLB disease involves both the pathogen and the immune response and their interaction. It’s a good balance.”

Learning more about how and when to stop this inverse relationship and how it varies among citrus cultivars may bring us closer to finding sustainable solutions to control this disease.

Levy’s research is published in the July issue Physiology of plants.

– Ruth Borger, UF/IFAS

https://www.morningagclips.com/citrus-greening-bacterias-complex-relationship-with-tree-defense-system/ The complex relationship of citrus greening bacteria with the tree’s defense system

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