A TIGER to Speed Citrus Disease Detection?

Gary Cooper Citrus

Passing along this news feature from Orlando Sentinel’s Jerry Jackson today, entitled,
“Researchers tout new test to detect threats to citrus”
Jerry W. Jackson | Sentinel Staff Writer
Posted December 21, 2006
The next time a disease such as citrus canker or greening surfaces in Florida or elsewhere, scientists should have a far easier time getting a quick fix on the culprit.
Researchers are buzzing about the potential for a new test said to be far faster and more thorough than existing screening techniques. The new tool, called TIGER — short for Triangulation Identification for Genetic Evaluation of Risks — will help scientists who are on the lookout for potentially dangerous diseases.

“TIGER is what you will turn to when something new shows up. And something else will come along,” said William Schneider, a plant pathologist with the Agricultural Research Service in Fort Detrick, Md.

“If TIGER had been around when greening first emerged as a problem, it would have really helped,” Schneider said. Greening is a bacterial disease now spreading in South Florida citrus that is considered in some ways far worse than canker because it not only kills trees but makes orange juice turn sour.

Many growers fear that greening has too much of a head start in spreading through the state and that research has been too slow, both in detection and finding controls or potential cures.

“We need to get our priorities straight and put more resources behind this. Greening is very scary,” said Maury Boyd, a lifelong citrus grower in west Orange County.

Citrus researchers last week announced a major new study to see if guava plants protect citrus against the psyllid insect that spreads the bacteria. Preliminary evidence from Vietnam shows substantial promise, according to scientists at the U.S. Department of Agriculture’s Horticultural Research Laboratory in Fort Pierce.

Boyd, whose family has been growing citrus in Orange County since the 1800s, said he was disturbed to learn recently that the greening bacteria is on a bioterrorism control list, a federal restriction that limits the ability of scientists to study the disease, even though it’s not harmful to humans.

Calvin Arnold, director of the USDA’s horticultural research lab, confirmed that greening is on several control lists originally intended to help keep it out of the country. But now that greening is in Florida it complicates, but does not prevent, research from going forward, Arnold said.

As for the new TIGER test, researchers say it is a significant advance in the detection field as the threat of bioterrorism, and economically damaging “agroterrorism,” grows.

There are several time-tested techniques for identifying pathogens such as bacteria, fungi and other microorganisms. They include visual identification through powerful microscopes and growing the pathogen in a lab culture. Another, more recent high-tech tool is the polymerase chain reaction, or PCR, test.

All have strengths and weaknesses, but the TIGER technique is faster and reveals more than the other forms of testing, the USDA’s Schneider said. Using fragments of nucleic acid called primers, the technique identifies a range of pathogens within minutes. More importantly, Schneider said, the test will note the presence of an unknown or unidentified pathogen and reveal its closest known genetic relatives.

“That really helps you focus, by identifying the closest relatives that we know about,” Schneider said. While the test won’t replace current methods of identifying canker and greening, it will add a new tool to the arsenal and help minimize the chance of missing some new pathogen, he said.

The TIGER test was developed by two California companies, but Schneider, with the USDA’s Foreign Disease-Weed Science Research Unit, is conducting his own research to help refine the technique. His work is in conjunction with the U.S. Army Medical Research Institute of Infectious Diseases, as part of its effort to detect human pathogens and bioterrorist agents.

Jerry W. Jackson can be reached at jwjackson@orlandosentinel.com or 407-420-5721