Exotic Australian Fruit May Help Save Florida's Citrus Industry

There's some good news in the long-running battle against a disease that's devastated Florida's signature crop, oranges. Researchers are developing tools to help control citrus greening, a disease that has killed thousands of acres of orange and grapefruit trees.

One of the most promising treatments was recently developed in a fruit most people have never heard of, the Australian finger lime. The finger lime, native to rainforests in Australia, looks a little like a pickle. It's just a couple inches long, grows on small trees and is gaining popularity as an exotic fruit.

Researcher Hailing Jin became interested in the fruit because it is related to oranges, but it isn't affected by citrus greening. Jin, a molecular geneticist at the University of California Riverside says, "When I heard that there are some wild citrus close relatives that show tolerance or partial resistance, then I (felt) like there must be some genes responsible for it."

In the 15 years since citrus greening first appeared in Florida, growers and researchers have scrambled for solutions. During that time, the disease has upended the industry. Orange production has plummeted, from nearly 300 million boxes in 2000 down to about 70 million boxes last year. The decline has cost jobs and forced the closure of packing houses and juice processing plants. The disease has now been found in commercial groves in Texas and in trees in residential areas in California.

About five years ago, Jin discovered the gene in finger limes that makes it tolerant to the disease. It produces a peptide, a natural antibiotic that kills the bacterium responsible for citrus greening. She's now developed a way to produce it in the lab. When it's injected into trees or sprayed on leaves, the peptide has a dramatic impact. Jin says, "The bacteria titer is largely reduced. And the symptoms, the disease symptom is also largely reduced. The new flesh, the new leaves look very green and healthy."

UC Riverside has partnered with a biotech company, Invaio Sciences to market the antimicrobial compound. Jin is hoping to start field trials soon in Florida orange groves and eventually get approval from federal regulators. Steven Callaham, the head of Dundee Citrus Growers says what he's seen so far is encouraging. "It still could be several years out before that particular solution could be commercialized," he says, "but it's very, very promising research. And that's just one thing of many I think you're going to see coming down the line."

In the battle against citrus greening, growers and researchers have been developing new orange varieties, new root stocks, and techniques like putting orchards in screened enclosures. Michael Rogers, the director of the University of Florida's Citrus Research and Education Center, says all that work is paying off. After years of declines, Florida's citrus production is stabilizing.

Rogers says, "When this disease first popped up in Florida, we said, 'Okay, the industry has about 10 years and it's going to be gone if we don't have solutions.' And it's not gone, but it's because we have found ways to live with citrus greening."

Rogers says the naturally-occurring compound from the Australian finger lime is one of dozens of peptides currently being investigated. Other promising research he says involves gene editing—removing the genes from orange trees that make them susceptible to the disease.

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