UF researchers hopeful canker can be managed

January 20, 2006

GAINESVILLE, Fla. — The fight to eradicate citrus canker from Florida ended last week when federal officials announced they’d stop funding removal of exposed trees, but researchers with the University of Florida’s Institute of Food and Agricultural Sciences are confident that in time the disease can be managed to ensure the future viability of the $9.1 billion Florida citrus industry.

The decision was spurred by scientific projections that the bacteria responsible for citrus canker disease had become much more widespread due to Hurricane Wilma in October 2005. The news will shift UF’s research priorities, said Jimmy Cheek, UF senior vice president for agriculture and natural resources.

“Up until now, we’ve had canker research proceeding along several tracks, one oriented toward eradication, others focused on detection, prevention and management practices,” Cheek said. “Since eradication will no longer be the strategy, we need to make sure we’re putting our resources where they’ll do the most good.”

Some existing UF canker programs will be enhanced, new options will be explored and time lines will be accelerated, he said.

“We are working closely with growers, as well as state and federal regulatory officials, to make sure their needs are addressed appropriately,” Cheek said. “Our overall goal is minimizing the impact canker and other diseases have on Florida’s citrus industry.”

UF extension faculty in citrus-producing counties will play a key role in the effort by communicating regularly with growers to obtain feedback and discuss new research developments, he said.

Canker is spread primarily by wind and rain, and causes citrus trees to develop small brown lesions and produce less fruit, said Harold Browning, statewide coordinator for UF citrus programs in teaching, research and extension. The current canker outbreak, discovered in 1995, was being contained until several hurricanes in 2004 and 2005 spread the bacteria over a much larger area.

UF experts are working with the Florida Department of Agriculture and Consumer Services, the U.S. Department of Agriculture, representatives of other agencies and the citrus industry to develop a statewide canker management plan and deliver its elements to the industry, said Browning, who also directs UF’s Citrus Research and Education Center in Lake Alfred.

The management plan will emphasize disease prevention, he said. Top priorities include protecting healthy trees in nurseries and groves, and ensuring proper sanitation during harvest and processing.

“We have been collaborating with citrus researchers in South America for the past 30 years, and we will try some of their canker-suppression strategies,” Browning said. “Brazil has a different climate, but their growers have been somewhat successful protecting groves with a combination of windbreaks, copper-based chemical sprays and decontamination procedures for personnel and equipment.”

Canker’s effect on Florida citrus production for the 2005-2006 growing season won’t be known for months, said Tom Spreen, chairman of UF’s food and resource economics department. Researchers are still assessing how far Hurricane Wilma spread the disease, and lawmakers must decide whether growers will be allowed to harvest fruit from exposed trees previously slated for destruction.

Spreen and his colleagues were completing a report on the future of Florida’s citrus industry when it was announced the eradication program would end. A revised report, updated to address the latest canker developments, will be issued in early March.

“We know there are a number of ways canker could have a negative economic impact on the industry,” Spreen said. “Reduced yield and increased production costs are possibilities. There could also be implications for the export market.”

Ensuring the quality of Florida’s citrus exports will be easier with the help of genetically modified canker bacteria that glow bright green when examined under special microscopes, said Jim Graham, a soil microbiologist at the Lake Alfred center who has tested a wide range of canker control strategies since 1999.

Along with post-doctoral associate Jaime Cubero, Graham led a research team that modified the bacteria with a gene derived from a species of jellyfish. The glowing microbes are far easier to detect than their normal counterparts, enabling faster, more accurate evaluation of sanitizing procedures.

“To test a sanitizing system, you can apply the bacteria to a test batch of citrus and simply run it through the system,” Graham said. “The bacteria only glow if they’re alive, so it’s easy to spot survivors and determine how well the system’s working.”

The modified bacteria will also help researchers learn how long canker bacteria survive outside citrus plant tissue, he said. This information will lead to more effective quarantine and grove-care practices to keep canker bacteria under control.

Citrus trees do not contain genes that specifically fight canker, but they have genes providing broad-spectrum disease resistance, said Gloria Moore, a UF professor of horticultural sciences. She is determining how citrus trees could be coaxed into expressing those genes more strongly, giving them a better chance of resisting canker and other pathogens.

In another study, Moore and Fred Gmitter, a horticultural sciences professor at the Lake Alfred center, lead a research team that has examined natural canker resistance in the kumquat, a fruiting plant closely related to citrus.

“One of our graduate students has isolated some of the genes that are responsible,” said Moore, who has researched canker genetics for the past five years. “By transferring those genes to citrus trees, we may be able to provide canker resistance.”

Rice is another plant with disease resistance UF researchers have borrowed for use in citrus, said Jude Grosser, a horticultural sciences professor at the Lake Alfred center. The grain has a gene that provides protection from rice bacterial blight, a disease closely related to citrus canker.

Doctoral student Ahmad Omar, working with Grosser, Graham and UF assistant professor of plant pathology Wen-Yuan Song, transferred the resistance gene to Hamlin orange trees, a project begun in 2000. The first of these trees is being assayed at a state Division of Plant Industry quarantine facility to determine if it can resist the most common strain of citrus canker bacteria.

If the test proves successful, the trees will be field-tested to evaluate their ability to resist canker and produce fruit in a real-world environment, Grosser said. Eventually they could become the first canker-resistant citrus variety UF makes available to growers.

“Genetics research has great potential to help the citrus industry overcome this threat,” he said. “We’re confident it will happen, and we’ve got a running start, thanks to all the work that’s been done already.”