Nabil Killiny, associate professor of plant pathology, checks bacteria samples at the University of Florida's Citrus Research and Education Center. Photo courtesy of Nabil Killiny/University of Florida
ORLANDO, Fla., Sept. 19 (UPI) -- Scientists believe they have made a key advance in understanding the bacteria that causes citrus greening, which has severely damaged citrus trees in Florida and Texas and threatens commercial groves in California.
A laboratory at Washington State University reported that it successfully grew the disease-causing bacteria, Candidatus Liberibacter asiaticus, for more than two years. Previous inability to grow the bacteria in labs for more than a few months has stymied efforts to identify treatments for the disease.
The results of the work were published online this month by the journal Biofilm.
Growing the bacteria in labs "will actually help a lot to find a solution and it will save millions of dollars," said Nabil Killiny, a University of Florida scientist who co-authored the article.
"Now we can screen thousands of compounds to see what will kill" the bacteria, Killiny said. "The antibiotics we've been trying to use had mixed results at best."
The study focused on growing the citrus greening bacteria along with other types of bacteria and with nutrients found in both citrus trees and in the psyllid bug that carries the disease.
Two challenges remain, according to the study. First, researchers must reconfirm the nature of the bacteria grown in the lab by reintroducing it into healthy citrus trees and seeing if the disease develops. Second, scientists still are trying to grow the bacteria by itself, apart from other bacteria.
Killiny said the methods used in the study for growing the bacteria will be available to anyone now via the published study, and he expects more experiments to continue around the world to identify best methods to kill the bacteria in citrus groves.
Psyllids were first discovered in the United States on the east coast of Florida in 1998, according to UF entomologists. That's also when citrus production hit a record high of 244 million boxes. But citrus greening and Hurricane Irma reduced that to just over 45 million boxes during the 2017-18 crop year. Last year's crop recovered a little, but still was one-fourth of the record high.
The state suffered a reduction of $4.6 billion of its gross domestic product in a five-year period after the disease took hold in 2006, according to UF statistics.
Infected leaves and stems for the study were collected at the UF Citrus Research and Education Center in central Florida and shipped overnight to Washington State University. Researchers there are anxious to move ahead.
"If we can test possible cures for the disease in a test tube, rather than by experimenting on trees, that will speed up the process of finding a cure," said David R. Gang, who runs the Gang Laboratory for Cellular Metabolism and Engineering at Washington State. "We will also be able to use other genetics tools on it and find ways to interfere with its growth."
The study was funded with a $2 million grant from the U.S. Department of Agriculture.