Washington is known for apples, but researchers at Washington State University — along with colleagues at the University of Florida — may have discovered a long-sought holy grail in the quest to stem citrus greening, the disease that has decimated the Florida's flagship crop.
WSU scientists are able to grow the bacteria that causes citrus greening — a major step in the creation of resistant plants or treatments for the disease. Among the researchers is David Gang, professor and director of the Tissue Imaging and Proteomics Laboratory at WSU.
"The expertise of everybody involved came together in the perfect combination. That's how we were able to come up with the idea to do this," Gang said. "We figured that there had to be something that everybody was missing — something about how the bacterium grows that people just weren't considering."
To grow the bacteria, researchers first needed samples of it. And that's where Nabil Killiny, UF associate professor in the Department of Plant Pathology Citrus Research and Education Center, comes in.
As part of his research, Killiny grows the insects that transmit the bacteria to trees and studies the nutrients they require. Killiny provided leaves and stems from infected Hamlin orange trees to the scientists at WSU.
From that, scientists were able to find the right recipe of oxygen, salts, acids, vitamins and other ingredients needed to promote long-term growth of a bacteria — something that had stymied earlier efforts.
"We always had the bacteria for short term, and then we would lose it. Now we have the bacteria for more than two years and can replicate it very nicely. It's perfect," Killiny said. "All of the samples are from Florida. Bacteria have so many strains, and it is possible that the strains in Texas are different from the strains in Florida or the strains in California. Now we have the Florida strain in culture, so Florida will be the first state to get benefits."
Data from Florida Citrus Mutual, a cooperative association of citrus growers, shows how the commercial growth of oranges has shriveled.
In 2003-04, Florida produced about 240 million boxes of the fruit, communications director Andrew Meadows said. Greening was found in 2005, and since then, about 70 million boxes a year have been harvested. About 850,000 acres were planted in oranges; now it's about 425,000 acres.
Not all of the decline is due to citrus greening, but Meadows said a big portion of it is. Meadows said the bacteria breakthrough is big.
"It's a step forward, most definitely. The research community has been trying to culture the bacteria since we started this fight more than a decade ago, so this is a huge advancement," Meadows said.
The biggest financial impact of the disease is on commercial growers. But citrus greening also kills trees that Florida residents have in their yards and love for the free fruit they provide.
Citrus greening is caused by the candidatus liberibacter asiaticus bacteria and is spread by the Asian citrus psyllid insect, which feeds on the stems and leaves, according to the Florida Department of Citrus.
WSU was awarded a $2 million grant from the U.S. Department of Agriculture two years ago to try to develop the bacteria. Killiny said UF got $500,000 from the grant for its role in the project. A researcher from the University of Arizona also worked on the project.
Citrus greening bacteria create biofilm — groups of cells that protect themselves by secreting protective or slimy compounds. The plaque on your teeth is from biofilm bacteria. So is methicillin-resistant staphylococcus aureus, the superbug known as MRSA.
WSU has experts in the field of reproducing bacteria, including Haluk Beyenal, an expert in biofilm culturing. He was able, using the right ingredients in the culturing medium, to grow the bacteria — and keep it growing.
"The biofilm was pretty much the critical thing. Haluk has figured out how to grow different biofilms," Gang said. "We're convinced that anybody who follows the methods we put together will be able to grow this bacteria. We've been able to make it grow now from different trees that have been infected."
More research needs to be done, but Killiny and Gang said eventually the work will lead to the development of orange trees that are more resistant to greening or to treatments for the disease.
"It will be much faster now, in my opinion. You can imagine how many compounds we can test now," Killiny said. "