The USDA calculates Florida’s citrus industry is producing half the oranges it did four years ago. The culprit? A bacterium called huanglongbing disease or “citrus greening.”
Right now, there is no known cure. And, if something isn’t done, the Florida Department of Citrus predicts production will fall to 18 percent of 2005 levels by 2026. A harvest of almost 150 million boxes reduced to 27 million.
It wasn’t long ago you could drive for hours through South Florida’s highways surrounded by acres of orange trees stretching back from the road and into the horizon. Blooming green and white in the spring, filling the air with their sharp, sweet fragrance.
But now, with the spread of HLB disease, South Florida’s postcard pastures are turning into wastelands.
The orchards look sick.
Skeletal dead branches claw through those still struggling to bear fruit. Oranges litter the ground below. And those are the trees that still have some life in them.
For some orchards, rows of dead trees line the roads, waiting to be plowed under.
Another citrus farm gone for good.
Since its discovery in the state in 2005, citrus greening has taken a chokehold on Florida’s citrus industry. The bacterium is carried by a citrus psyllid– a tiny insect that feeds on citrus trees. The bacterium infects the tree when the psyllid feeds on the sap. Sometimes symptoms don’t appear for years.
The bacterium infects the phloem– the tissue that transports nutrients throughout the tree. This causes fruit to become bitter and fall off before fully ripening. It has cost growers nearly $8 billion in revenue, according to UF/IFAS reports.
Genetics Institute faculty are using $6 million in grants from the USDA to find a cure.
Last year, a team organized by Graciela Lorca, associate professor in the department of microbiology and cell science, began pursuing possible antimicrobial treatments for the disease, with the help of a $2 million grant from the USDA.
The research group includes UFGI faculty members Ana Conesa, Salvador Gezan, Claudio Gonzalez, Jose Chaparro and Max Teplitski, and UF researchers Svetlana Folimonova and Kelly Grogan.
Collaborating with fellow UFGI faculty member Claudio Gonzalez, Lorca’s team approached the problem by identifying significant proteins necessary for RNA transcription within the bacterium, Next, they began looking for chemicals that would bind to those proteins.
Once the chemical binds to the protein, it is rendered inactive, meaning the bacterium can no longer express its own DNA.
“If the bacteria cannot express the genes that it needs to survive the environment in the plant, then we hope it will die,” Lorca said.
So far, the antimicrobial chemical has shown promise. They’ve been testing the antimicrobial chemical on trees that are a couple years old, and Lorca said the results are encouraging.
To treat the trees, they inject them with the antibacterial chemical, and then measure bacterial titers to monitor efficacy.
Some trees showed significant improvement after only a couple months, while sicker trees took several months.
Meanwhile, they have also been testing the chemical on older, larger trees in a grove, and will have the results of that yearlong study in April.
In March, researchers will begin applying to the chemicals to infected trees on three commercial orchards in Florida.
One of the difficulties about treating the disease is the difficulty culturing it in a lab. The bacterium makes its home in the phloem of trees, and researchers have not been able to culture more than a few generations outside the plant.
UFGI faculty member Dean Gabriel persuaded the USDA to give his team a $4 million grant to tackle that very problem. Gabriel, a professor of plant pathology, is working with faculty from multiple institutions to figure out a way to culture the bacterium.
“It’s been very frustrating, because that’s impractical for any functional genomics analysis,” Gabriel said. “You can’t grow the bacteria, you can’t genetically manipulate them, and you can’t even inoculate plants for testing purposes. The bacteria are present in such minute quantities it requires PCR just to detect it.”
When geneticists first began studying HLB, they never expected this to be an obstacle, Gabriel said.
They expected to be able to analyze the genome for markers that would offer insight into the pathology of the disease– molecular targets they might be able to disrupt.
Unfortunately, they couldn’t keep it alive long enough to do that.
“Your ordinary toolset as a biologist is off-limits right now,” Gabriel said.
But he’s optimistic his team of microbiologists and geneticists– including “experts in culturing oddball bacteria”– have the skills to find a way.
“This thing has really defied normal expectations,” Gabriel said. “And there probably are two or three genetic elements that are combining to prevent culture, so even if you got one of them right, you still don’t have the combination to the safe.”
His group plans to attack the problem by analyzing the bacterium’s genes– identifying missing or active genes that are preventing researchers from culturing the bacterium.
They also plan to use micro-fluidic chambers, and media that promote the growth of similar bacteria.
“We’re going to try to develop mechanism of using and modifying phage in order to get at this genome,” Gabriel said. “The issue is– how do you select the modified organism when you can’t culture it?”
And they’re running out of time.
Gabriel predicts, without the arrival of an effective treatment, Florida’s citrus production will drop by 50 percent in the next four or five years.
Even now, some farmers are putting so much money into attempting to treat their trees, come harvest time, they realize it will put them in the hole to pick the fruit.
Some juicing plants have already closed. Gabriel predicted they won’t be coming back.