Citrus greening, Huanglangbing: Dozens of scientists working on the bacterial disease

FORT PIERCE, Fla. - There are acres of laboratories and greenhouses in Fort Pierce's USDA laboratory.  More than half of the work being done currently in the lab is devoted to Huanglangbing, better known as citrus greening.

"It is the problem that nobody wanted and we have it," explained Mark Hilf, a research plant pathologist.

Hilf is one of dozens of scientists working on the bacterial disease. 

The Florida Department of Agriculture says Florida accounts for more than 63 percent of the total U.S. citrus production.  There is a total direct and indirect economic impact of more than $8.9 billion.  It is impossible to predict the future effects of the widespread disease. 

Citrus farmers statewide have invested millions of dollars out of pocket on the research, hoping for a cure.  Laboratory Director Calvin Arnold, Ph.D. believes $16 million has been spent by farmers this year.  One quarter of that goes directly to the USDA laboratory.

Hilt explained, "On an individual tree there really is no cure, and even if you were able to treat a tree to get rid of the bacterium, there is also the problem of reinfection by the insects."

In one greenhouse, scientists rear the "psyllid," the tiny insect that spreads the disease.  One group of scientists is looking for ways to block the insects from feeding using tiny, artificial diet chambers.   

"We are able to add things to these diets, to find molecules that will block different biological activity of these insects," said Bob Shatters, a research molecular biologist. 

Shatters says the team has discovered breakthrough information that may also help with other diseases.

"If they can't get to the vascular tissue of the plant, they can't pick it up or deliver the bacteria," he said.

Other groups of scientists are working to build more tolerant plants that produce high-quality fruits.

Horticulturist Ed Stover says there is some promise in finding things that can grow in the presence of the disease.

"Trying to develop new citrus varieties that incorporate tolerance or resistance to huanglong bing," Stover said.

Others are finding treatments for trees that are already infected.  The genome of the citrus greening disease has been mapped. 

"In our work, we have to balance our enthusiasm for what appears promising, and conservatism in terms of our level of certainty that things will have value," explained Stover.

Yongping Duan, a research plant pathologist, says they have had success under temperature-controlled environments using small, portable greenhouses around trees.

"The heat treatment actually help the plant recover," he said.

The problem, however, is in applying the science to a grand scale.  The treatments must be made possible for application on up to 532,000 acres of commercial citrus.  They must also be affordable for working farmers.

"In essence if there ever was a monster in terms of a plant disease, this one is it," Hilf said.

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