One March morning, more than 80 years after his family first started growing oranges in DeLeon Springs, Steve Crump stood on the same land, shaking his head in frustration.
The fourth-generation farmer was surveying a cluster of orange trees he said were infected — just like the rest of his trees — with deadly “citrus greening,” a bacterial disease with no cure. The infection grows from a pathogen spread by the Asian citrus psyllid, an invasive insect that appeared in Florida in 2005.
In the time since, the disease has “decimated” the Sunshine State’s trademark citrus industry, Crump said. That includes in his own orange groves here at Vo-LaSalle Farms, where Crump notes production is down 80% since he first noticed signs of greening, 15 years ago.
“It’s very discouraging,” Crump said. “I know how to grow an orange tree, or at least I used to know how to grow an orange tree. I really don't anymore.”
At least, that's what it can feel like these days, for citrus farmers like Crump: “an uphill battle,” as the American Farm Bureau Federation puts it.
In its prime, Florida citrus was booming; the state churned out more than 13 million tons of product during the 2003-04 season. During the most recent harvest season, Florida produced more than 90% less than that.
“We got a combination of hurricane after hurricane, every five years — devastating hurricanes — and then citrus greening disease,” Crump said. “Every time there was a hurricane, production would drop by half.”
In 2020, Crump brainstormed a way to try and help his trees survive citrus greening, he said. He built a 2.5-acre “screenhouse,” complete with roof and roll-up door, where the trees could grow: safe from the psyllid insect.
For a while, Crump’s plan was working great. The citrus trees insulated in his screenhouse grew to be roughly ten feet tall, or three times higher than they’d typically grow outside, Crump said.
But the hurricane season of 2022 had other plans.
“This is an unbelievably great way to grow trees, until you have a hurricane,” Crump said. “Then the roof splits, and the sides blow in. And the bugs come.”
When Hurricanes Ian and Nicole hit the area just a few weeks apart, Crump had to repair the damaged screenhouse — once, then twice. Earlier this year, he noticed signs of citrus greening on the trees inside.
“That was discouraging,” Crump said.
With citrus greening disease, “everything that should work, and used to work, isn’t working like it’s supposed to,” Crump said.
Searching for solutions
In Central Florida, scientists are leading the global search for citrus greening solutions.
Nian Wang, a microbiology and cell science professor at the University of Florida's Institute of Food and Agricultural Sciences, works at UF/IFAS’ Citrus Research And Education Center (CREC) in Polk County. In 2022, Wang says his lab there became the world’s first to develop a gene-editing technology called CRISPR for citrus applications.
CRISPR stands for “Clustered Regularly Interspaced Short Palindromic Repeats.” It allows scientists to potentially treat certain diseases, by targeting specific stretches of genetic code and making precise edits to DNA.
“It's like a scissor, but a molecular scissor,” Wang said of CRISPR. “It cuts the chromosome of the [citrus plant], to try to remove … the gene that makes the plant susceptible to the pathogen.”
At the same time, it’s important to avoid accidentally removing “a good guy” — Wang’s nickname for a good piece of DNA — along with whichever problematic gene researchers are targeting with CRISPR. Otherwise, removing good DNA could trigger negative impacts, like lower-quality fruit yield, for the modified trees.
“You want to make sure that you know what is responsible for the disease,” Wang said.
That process of isolating “bad guy” genes gets more or less complicated, depending on the specific plant and disease. For example, Wang’s team already finished running successful CRISPR experiments on citrus trees planted and infected with another disease, citrus canker. In late 2022, the USDA approved those canker trees: the world’s first, non-genetically modified citrus variety generated by CRISPR, Wang said.
While working with those canker trees, Wang’s team only had one “bad guy” gene to focus on. Now, for citrus greening, they’re looking at 40 different, potentially “bad guy” genes all at once, Wang said. It’s one reason why he thinks finding a reliable, long-term citrus greening solution will be a longer process.
Another factor is citrus trees’ relatively long juvenility, or puberty stage, Wang said. For example, he says the sweet orange tree typically spends 7-8 years growing before it starts to flower, generating fruit.
“That's why traditional breeding takes so long,” Wang said. “[CRISPR gene editing] can speed up the process.”
Right now, Wang’s team is trying to further improve the CRISPR technology’s capacity to help citrus trees bypass juvenility. Even still, it takes quite a while for psyllid insects to feed on the CRISPR trees and infect them, before citrus greening symptoms appear about 14 months later.
In March, Wang’s team planted two rounds of CRISPR trees in a Central Florida field: more than 120 citrus trees in all. So far, all the trees are surviving and none are showing citrus greening symptoms, Wang said.
Early results look promising, but long-term, it’s still way too soon to say how resistant these CRISPR trees will be to citrus greening, Wang said.
“I think we have the HLB-resistant, [and/or] tolerant plant,” Wang said, using another name for citrus greening: HLB, or Huanglongbing. “We just need to … have data, to convince growers they are HLB-resistant [and/or] tolerant … with no major negative side effects.”
“It’s kind of a long, slow process [for] the disease development,” Wang said.
A light at the end of the tunnel?
Back at Vo-LaSalle Farms, Steve Crump is trying to be patient. As it is, he thinks he needs to remove about half of all his orange trees, after citrus greening rendered them unproductive.
Like Crump, Bill Linen’s farming backstory goes back generations. Today Linen says he owns 1,000 acres of citrus groves, mostly in Lake County; he manages most of it on behalf of other growers, while keeping a 190-acre plot for himself.
Particularly for farmers in Central Florida, citrus greening exacerbates other, major stressors, Linen said.
“The pressure of the housing market and things like that just make it more difficult to stay in citrus or any farming business, especially in Central Florida,” Linen said.
More than just a job, farming is an entire way of life, according to Linen, and it’s a hard thing to imagine giving up. But farmers may feel like they have no other choice, amid rising operational costs, plummeting crop production numbers and rich developers hungry for new subdivisions.
“The price they’re willing to pay for your farmland, you could have generations that would not make as much money,” Linen said.
As financial pressures from citrus greening and other factors compound, some farmers are left struggling to hold on not just to their business, but their very way of life.
“It's hard to keep living that dream year after year, and not really seeing much light at the end of the tunnel,” Linen said.
But meanwhile, Wang is hopeful. Next year, he says he expects to know more about his CRISPR trees’ level of resistance to citrus greening.
“I think that the solution is getting closer and closer,” Wang said.
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