USDA seeks input on bio-control agent aimed at citrus greening disease


Greening disease, a bacterial disease spread by a tiny psyllid, has devastated Florida’s citrus industry since it was first detected in the U.S. in Florida in 2005 — but hopes of stopping or slowing its spread have risen this week.

While there’s no cure, on Monday the U.S. Department of Agriculture announced an important next step in the quest to stop the disease. The key to thwarting the disease’s march could lie in spinach proteins that scientists at Southern Gardens Citrus, a subsidiary of Clewiston-based U.S. Sugar, have been working with under strict research regulations for years.

The agency’s Animal and Plant Health Inspection Service said that in response to Southern Gardens’ permit application, it intends to prepare a draft environmental impact statement. The EIS will evaluate what the impact might be from the potential approval of the permit application for the release of a genetically engineered citrus tristeza virus that’s been bolstered with proteins from spinach the fight the bacterium.

Tim Eyrich, Southern Gardens’ vice president of research and commercialization, said Tuesday he doesn’t view the fortified virus as a silver bullet, but rather as a tool that once it is fully developed, growers can use to manage greening.

Spinach proteins, or technically “antimocrobial peptides” are inserted into CTV, a naturally occurring virus found in all citrus. The virus then expresses the defensin proteins from spinach, which act against the greening bacterium.

The USDA said that the release of the GE CTV does not involve genetically engineering citrus trees, and that using the CTV will have no impact on the genetics of the trees. The trees themselves are not changed.

“However, APHIS has decided to prepare an EIS to better understand the potential for environmental impacts associated with the issuance of a permit,” the notice states.

The genetically engineered CTV expressing the proteins to control greening disease has been field tested in Hendry and Polk counties since June 2010 under confined conditions that restrict the virus to the field test site, the USDA stated in the Federal Register.

“Our hope is to provide a tree that brings a level of production back to the grower that would allow him to make a good decision on replanting and reinvest in Florida citrus,” Eyrich said.

Eyrich said the trees inoculated with the GE CTV still may contract greening, but hopefully the trees will grow normally despite that. The permit is needed so that more field trials can be conducted and more data collected. Eyrich is hopeful that if all goes well a solution can be available to growers within the next few years.

Southern Gardens’ research director Mike Irey and Eyrich have led the research, which Southern Gardens has solely funded into the millions of dollars. Researchers at the University of Florida and Texas A&M University are working with the Southern Gardens’ team.

In September 2005, USDA scientists confirmed the first U.S. detection of greening on samples of pummelo leaves and fruit from a Miami-Dade County grove. It is now endemic to Florida and found in every citrus-producing county.

The symptoms include yellow shoots, mottled leaves, twig death, tree decline and reduced fruit size and quality. Affected fruit tastes bitter, medicinal and sour. Symptoms don’t show up for an average of two years following infection.

The disease is spread by the Asian citrus psyllid, which was first detected in the U.S. in Delray Beach in 1998.



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