A molecular geneticist from the University of California, Riverside, has discovered a novel class of antimicrobial peptide — a naturally occurring compound produced by citrus trees — which may help to treat the dreaded citrus greening disease that poses a threat to California’s citrus industry.
The disease, also known as huanglongbing or HLB, already has infected up to 90% of the citrus trees in Florida and has been found in Texas as well.
So far, although it has been detected in Southern California, mostly in trees in residential neighborhoods, it has not yet made its way to the state’s major commercial growing region in the Central Valley, and California’s citrus growers would like to keep it that way.
A treatment developed by Hailing Jin, a professor in the university’s microbiology and plant pathology department, has shown some success at controlling the disease, she said.
After a five-year search, Jin found a treatment using a naturally occurring molecule — a peptide found in wild Australian finger limes — that can inhibit the bacteria that cause the disease.
Though a rarity in the U.S., Australian finger limes are found in upscale restaurants in places like England, France, Italy and Australia.
Working with collaborators at the University of California, Davis, Jin treated several sets of infected trees in a greenhouse, including some that were in such bad shape that they were about to be thrown out.
Results were detected in as little as 60 days.
“All the sick trees survived,” she said.
Some severely infected trees had sprouted new leaves within two months and showed no symptoms of citrus greening, Jin said.
The treatment has a number of advantages over the antibiotics used to treat the disease in Florida, she said.
It should be relatively safe for humans, since it already is found in the food chain — in the finger lime fruits — and is easily digested by humans and animals, and it remains stable in temperatures up to 140 F.
Most antibiotics are sensitive to high temperatures and lose their effectiveness in hot weather, which is common in regions where citrus trees grow, Jin said.
The treatment can be injected into the tree trunk or sprayed over the entire tree.
While spraying may be appropriate for smaller trees, the injection method likely would be more cost effective for larger ones, she said.
The treatment needs only to be applied every two to three months.
The peptide has a dual function — it treats infected trees, and it also can induce a plant’s innate immunity and be used as a vaccine-like solution to protect healthy ones.
So far, she said the peptide has been effective in controlling HLB in greenhouse trials in the UC Davis Biosecurity Level 3 facility.
The next step will be field trials on more mature trees in actual citrus groves in Florida.
Those tests were scheduled to begin shortly after mid-October.
The trials were expected to get underway late last year but were delayed by the COVID-19 pandemic.
The university has granted Cambridge, Mass.-based Invaio Sciences an exclusive license to manufacture the treatment. P
Invaio also will provide proprietary injection technology that will ensure the peptide is injected effectively, and the company will help guide the finalized treatment through the vigorous regulatory approval process established by the U.S. Environmental Protection Agency, Jin said.
The treatment would be of particular significance to California growers since that state produces about 90% of the fresh citrus fruits in the U.S.
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