Click for full image. Caption at the bottom of the story.

GAINESVILLE, Fla. — University of Florida researchers have shown that the disease that threatens to devastate the world’s citrus crop is almost certainly the result of a lone species of bacteria, and not that of a combination of bacterial or viral pathogens as some have feared.

Using three types of next-generation genetic analysis, researchers from UF’s Institute of Food and Agricultural Sciences examined inner bark from Florida citrus trees infected with citrus greening.

While the team conclusively found the genetic fingerprint of the bacteria commonly suspected to be behind the disease, Candidatus Liberibacter asiaticus, the analysis showed no other DNA of suspect viral or bacterial pathogens.

The research, published in the December issue of the journal Molecular Plant-Microbe Interactions, is important because the disease has been especially difficult to analyze, said Eric Triplett, chairman of UF’s department of microbiology and cell sciences and lead researcher on the study.

Normally, researchers would prove that the bacteria is behind the disease by capturing a sample of the bacteria, growing it in a petri dish, and then inserting it into a healthy tree to see if it causes the disease.

However, scientists have not yet found a way to get the bacteria to grow in a petri dish. This means that scientists are having trouble using their normal approaches to researching the pathogen.

This genetic analysis is just one of the innovative ways UF researchers have dealt with the irksome bacteria. For example, researchers have developed complex 3-D computer models of the bacteria in infected tree tissue, while other efforts have focused on stopping the insects that spread the pathogen.

“This research tells us that our work, much of which has been focused on Liberibacter, is dead-on, on-target,” said Jacqueline Burns, director of the UF/IFAS Citrus Research and Education Center at Lake Alfred. “And it gives us confidence to move on with research that helps target this pathogen.”

Along with potential treatments, the genetic analysis could help lead to new quick and inexpensive testing methods that can be early indicators of disease.

Greening slowly weakens and kills all types of citrus trees, while making their fruit malformed and discolored. However, one of the most problematic issues with greening is that infected trees often go years before showing any of these symptoms.

This gives the disease plenty of time to spread without detection. Since there is currently no cure for greening, the only solution is to destroy infected and possibly infected trees.
So far, greening has devastated citrus crops in Asia, Africa, the Arabian Peninsula and Brazil.

In the U.S., it has been sporadically found through Louisiana, Georgia and South Carolina. The biggest presence, however, is in Florida. Since its presence was first confirmed in Florida in 2005, it has been found in 34 counties — making it a major threat to the state’s $9.1 billion citrus industry.

Contacts:
Writer: Stu Hutson, 352-273-3569, stu@ufl.edu
Sources: Eric Triplett, 352-392-1906, ewt@ufl.edu
Jacqueline Burns, 863-956-1151, ext. 1285,
jkbu@ufl.edu

Caption:

This 3-D illustration released by the University of Florida’s Institute of Food and Agricultural Sciences is a computer model of a piece of tissue from the inner bark of an orange tree that is infected with citrus greening (the various finger-like objects are the bacteria suspected to cause the plant disease).

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