A protein can help make some citrus more tolerant to the deadly citrus greening disease — and it’s safe

Greening disease has devastated the citrus crop in Florida, but University of Florida scientists are using genes from another plant and putting them into Hamlin oranges to develop citrus plants that fight the disease.

Scientists have developed a plant they’re calling NuCitrus. It’s based on a protein called Arabidopsis NPR1. This new citrus shows strong tolerance to citrus greening, but not resistance.

Tolerance means plants can be infected by the pathogen but show no symptoms or only mild symptoms, which do not affect yield or quality. Resistance means that the plant can barely be infected.

NuCitrus plants not only tolerate disease attacks, they produce high-quality fruit, said Eric Triplett, Ph.D., a professor and chair of microbiology and cell science at the UF Institute of Food and Agricultural Sciences (UF/IFAS). The added gene in NuCitrus produces a natural protein that is common in many foods such as broccoli and cauliflower. 

“Working with the UF/IFAS Crop Transformation Center, NuCitrus was developed by adding a gene to citrus that boosts its own natural defense system,” said Triplett, a co-lead author on the new paper.

“Our recent paper shows that very little of this protein is found in NuCitrus fruit, it’s not toxic to humans, and, if eaten, is rapidly digested in the stomach, just as it is with other vegetables that contain it,” said Zhonglin Mou, Ph.D., a UF/IFAS plant immunity professor and lead author of the paper. “The added protein is not even toxic to the microorganism that causes citrus greening disease.”  

Now, Mou’s team is working to propagate lots of NuCitrus plants from the existing ones for large-scale field testing and to obtain federal approval to use NuCitrus for high-quality orange juice in the future.

“I expect NuCitrus lines to become an important tool in the toolbox in the battle against the disease,” Triplett said. “I expect these lines to work well in well-managed groves where the latest nutritional advances and psyllid-control measures are in place.”

Psyllids are the insects that infect citrus with the greening disease.

UF/IFAS researchers are working with a nursery to expand the number of plants available quickly, he said. This will take time to provide the scale needed. Approvals by the EPA and the Food and Drug Administration for commercial use are expected in less than two years.  A USDA permit has been granted for experimental use such as for yield trials.

The pathogen-free plants will be available to growers once EPA and FDA approvals are obtained, Mou said.