Win32 Virus Removal

That's some of the good news that surfaced this week during the Second International Research Conference on Huanglongbing in Orlando. Scientists summarized key findings during a Friday morning session called "Grower Day."

About 400 scientists from 20 countries gave 75 lectures on their greening-related research this week.

Huanglongbing is the Chinese name for citrus greening, a deadly bacterial disease that threatens the existence of commercial citrus growing in Florida, Brazil and other countries.

"I think this meeting has highlighted how much progress has been made in finding solutions," said Jackie Burns, interim director of the University of Florida's Citrus Research and Education Center in Lake Alfred. "Now we have a suite of possibilities."

One possibility stems from research done by William Dawson, a plant pathologist at the Lake Alfred center, who developed a genetically modified form of the citrus Tristeza virus that can introduce new genes into a citrus tree, Burns said. Other researchers have found several promising genes that might immunize or increase resistance to the greening bacteria.

"We have a gun now. We just need to find the bullets," she said.

The normal Tristeza virus is fatal to citrus trees, but Dawson modified the virus to be harmless, Burns said. But its modified form will still spread throughout the tree, introducing whatever genes it would carry.

Use of the modified Tristeza virus is still a long way off because of the need for further research and regulatory issues, she said.

Surveys suggest the overall greening infection rate in Florida is 18 percent and doubling every year. But rates in Central Florida, including Polk, and areas to the north and west are much less, estimated at just 1 percent.

On a shorter time horizon, researchers have developed a simple field test to confirm the presence of greening bacteria in a tree, said Tim Schubert, an administrator at the Division of Plant Industry at the Florida Department of Agriculture and Consumer Services in Gainesville.

Currently only a lab test can confirm the bacteria.

The new field test is not as sensitive as the lab test, but it can still help growers.

"An extremely sensitive test is probably not what is needed in the field for management decisions," Schubert said.

What's important for management decisions is not whether an individual tree is infected but the extent of greening disease in the entire grove, he said.

Even with the lab test, a single tree shown positive for greening means at least two more and as many as 50 more trees are probably infected, said Schubert, who did not know how soon the test would be commercially available.

Schubert also reported researchers have found two strains of the greening bacteria in the U.S., suggesting two separate introductions and that greening existed in Florida much longer than 2005, when scientists confirmed the first case in the Homestead area.

Both Florida strains are most closely related to the Chinese strain of the disease, one of four strains identified globally, he said.

That suggests the disease was introduced from China and not Brazil, which has a separate strain not as closely related. The fourth strain came from India.

Some bad news also surfaced from the research, however.

The Asian citrus psyllid, a greening bacteria host and the main vehicle for spreading the disease, has developed biological resistance to 12 pesticides commonly used in Florida, said Lukasz Stelinski, an entomologist at the Lake Alfred center.

Also, Yulu Xia, a Chinese researcher, reported that country's experience with enhanced nutrition programs shows the program can keep a tree productive for only about eight years.

Various nutrition programs to maintain fruit production from infected trees, popularized by Winter Garden-based grower Maury Boyd, have gained popularity, especially in highly infected South Florida.

The programs are an alternative to the traditional method, which calls for removing infected trees as soon as possible.

Chris Oswalt, a citrus extension agent Polk County, said research shows it is more economical to halt tree removal and switch to a nutritional program, at least in the short term, once infection rates reach 4 to 5 percent.

[ Kevin Bouffard can be reached at kevin.bouffard@theledger.com or at 863-422-6800. Read more on Florida citrus on his Facebook page, Florida Citrus Witness, http://bit.ly/baxWuU. ]