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Chemical cure for citrus greening being studied

— It may not be the magic bullet, but so far, citrus researchers and growers think it’s on target.

Chemicals that are found in treatments for human gout are showing signs of being capable of also staving off the citrus bacterial disease called “greening.”

According to a June 4 report from the University of Florida Institute of Food and Agricultural Sciences (IFAS), a team of scientists is focusing research on three antimicrobial chemicals that could lead to an effective treatment for citrus “greening” — a bacterial disease that could possibly shut down Florida’s citrus industry.

Huanlongbing, known as “citrus greening disease,” is the most harmful citrus disease in the world, according to IFAS Florida. Growers around the state spend about $250 million a year battling greening, spread by two psyllid insect species. The disease causes citrus plants to produce “green, misshapen, bitter-tasting fruit.”

So far, UF researchers found five new antimicrobial molecules may combat greening and citrus canker and the compounds — benzbromarone, used to treat gout; phloretin, a natural chemical found in apples; and hexestrol, an estrogen compound — seem to be effective against the bacteria and may ultimately lead to a treatment and cure for infected trees.

IFAS reports on average, the $2.6 billion U.S. citrus industry produces more than 11.6 million tons of citrus fruit each year with Florida, California, Arizona and Texas producing the most.

Highlands County has approximately 63,000 acres of citrus groves, which comprises roughly 13 percent of the county’s 1,000 square miles of land. The goal is to eventually eliminate greening, which has cost Florida’s economy an estimated $3.65 billion in lost revenues and 6,700 jobs since 2006 by reducing orange juice production, according to an IFAS study.

Graciela Lorea, a UF associate professor of microbiology and cell science, is the leader of a three-year research project focusing on benzbromarone as a greening treatment or cure.

Lorea, who heads the study with Claudio Gonzalez — a UF associate professor of microbiology in Gainesville — said Friday the research is giving promising results in the university’s laboratories. She said greening bacteria is dying in lab-specimen studies and researchers are now studying results using greenhouse citrus trees, with results available “in the next few months.” She said the study is only in its third year and it would be at least five years before the study would be taken to the groves.

“We have high expectations but are very optimistic,” she said. “We’re hoping this is the key to curing greening.”

Lorea said for the study, IFAS is looking for continued funding from the U.S. Department of Agriculture and the Citrus Research and Development Foundation, a non-profit corporation based in Lake Alfred that is a direct-service organization of the University of Florida to study advance citrus disease and production research.

Lorea said what makes research tough is that any studies on an anti-greening agent needs to be done with grove trees; the bacteria can’t be grown in a lab. Researchers are studying the bacteria’s genetic code, looking for proteins critical to bacteria survival in its host plant.

In the lab, Lorea and other scientists experimented pathogens-sharing proteins important for bacteria survival that could be cultured. The pathogens were hit with antimicrobial chemicals and monitored for interaction with the proteins. She said the result was the three agents bound with a protein in the greening bacterium, got in the way of the cell wall remodeling process necessary for survival inside a tree.

Studies showed benzbromarone worked 80 percent of the time and was the most effect chemical agent.

Growers are hopefully optimistic a cure may be on the way, but caution a lot of study in the field remains to be done.

Ellis Hunt Jr., president of Hunt Bros Inc. citrus growers, Lake Wales, and on the Florida Citrus Commission, said so far, studies have just been done in labs and it is too early to call the antimicrobial chemicals a solution to greening.

Hunt Bros. has about 5,000 acres of citrus in Lake Wales, Labelle and Immokalee and has been in the citrus business since 1922. Hunt said studies have just been done in greenhouse environments and it’s much too early to call benzbromarone and other chemicals solutions for greening.

“Ultimately, everyone is hoping for something that will save the industry and whether this could be it remains to be seen,” he said. “We’re all hoping a cure comes quickly; we need it tomorrow.”

Citrus industry experts like Hunt and Ray Royce, Highlands County Citrus Growers Association executive director, said it could be five to seven years before a new active-ingredient product could be commercially available because of the amount of time field testing takes and government regulations. Royce said the chemical agent studies are “very promising” but wouldn’t be immediately available and a lot of laboratory work still needed to be done.

“Often, things show promise in the lab, but then you have to figure out the commercial application,” said Royce, who spent 20 years as a citrus grower. “The exciting thing is people are still looking into it unique ways to battle greening and this may even spark something new.”

Lorca and Gonzalez are currently spraying agents on young seedlings in a greenhouse. If those tests are positive, they plan to take the treatments into the groves on young trees and eventually mature citrus trees.


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