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Although the bacteria have a head start, scientists are making inroads in the search for a way to vanquish the costly disease.
By THOMAS C. TOBIN
© St. Petersburg Times, published June 30, 2002
As canker bacteria march north out of Miami, their only goal is to make war on orange and grapefruit plants. Yet the bacteria have managed to throw human bystanders into a battle of their own.
Hard words fly back and forth over the state's effort to eradicate canker by cutting down backyard citrus trees. Bureaucrats have been called Nazis. Angry homeowners have been portrayed as fools, unwilling to look beyond their property lines at a looming disaster for Florida's $9-billion citrus industry.
But in fluorescent-lit laboratories in Florida, another canker battle is under way. This one is quieter. Microscopic.
A group of Florida scientists, armed with nearly $5-million in new federal grants, are restarting the quest for a citrus canker cure.
One of the scientists has invented a way to outsmart the canker bacteria with protein "blockers." Another hopes to isolate canker-resistant genes found in hearty citrus plants such as kumquats, and "transport" those genes into the popular Florida orange and grapefruit varieties.
But the scientists say a cure is 10 to 20 years away.
"Time is really on the side of the disease at this point," said James H. Graham, who coordinates citrus canker research at the University of Florida's Citrus Research & Education Center in Lake Alfred.
So far, the state has resorted to the primitive method of cutting down nearly 2.2-million trees since 1995 -- even healthy ones -- to prevent the spread of canker. After a two-year court fight, a Broward County judge earlier this month silenced most of the state's chain saws. Next stop: a Florida appeals court.
The enemy is a class of bacteria named Xanthomonas, (pronounced ZAN tha monas) the father of substances such as xanthan gum, a principal ingredient in Gummy Bears and Miracle Whip.
Xanthomonas also causes canker. It attaches its round, needle-covered body to a citrus cell and uses one of those needles to inject a bit of protein. The protein travels to the nucleus of the cell with a message telling the cell to divide. The cell complies.
Multiplied many times, this process causes brown spots on citrus leaves and fruit that humans recognize as canker.
The fruit on citrus trees drops too early, which means less juice and fewer profits. The fruit that doesn't drop is discolored and unacceptable to consumers.
But wait.
Enter one of the good guys, a genetically manipulated protein molecule called a "blocker."
When scientists inject a blocker into a citrus cell, it zeroes in on the foreign protein molecule sent by Xanthomonas. It binds to it, and recruits other molecules to bind to it as well.
Then the coup de grace: It grabs the Xanthomonas protein in two places and twists it in a kind of microscopic wrestling move that would make Jesse Ventura proud.
The Xanthomonas protein is rendered useless and canker is averted.
But not for long. In experiments so far, Xanthomonas has managed to overwhelm the blocker over time. So the quest continues for a blocker that will throw Xanthomonas to the mat for good, and make citrus immune from canker.
Who will find the solution?
Meet the state's most senior experts on canker.
James H. Graham, of UF's Lake Alfred citrus research center, is a 50-year-old jazz fan who often travels to Brazil and Europe for his work.
Dean W. Gabriel, 51, is a prominent UF professor with a talent for expressing DNA science in simple terms -- a byproduct of explaining what he does to his five children. He also is a novice businessman whose startup biotechnology company in Alachua, near Gainesville, is working to perfect the molecular wrestling move on Xanthomonas.
Gabriel hopes to sell his solution to the citrus industry someday.
The two men came to Florida in the mid 1980s, still in their mid 30s. They were hired to explore the mysteries of citrus, and quickly found themselves focused on the canker problem.
Now, with children in college, they look forward to a cure that won't likely come until they approach retirement. For them, the word Xanthomonas trips off the tongue with ease after careers spent trying to unlock the bacteria's secrets.
"I sort of loved citrus, and I worked on canker for a long time and I'd really like to beat the thing," Gabriel said in mid-June, soon after Broward County Circuit Judge J. Leonard Fleet halted the state's controversial tree-cutting program.
Gabriel and Graham said the judge's action, if allowed to stand, will almost certainly lead to the spread of canker in South Florida and other areas of the state. The hurricane season could spread it further.
On a Spartan campus of beige buildings just outside tiny Lake Alfred, near Winter Haven, Graham and a handful of fellow scientists are starting work that is similar to Gabriel's experiments in Alachua. The work also involves changing the genetic makeup of citrus plants.
Gabriel has invented a way to outsmart the canker bacteria (the rogue, Xanthomonas) with blockers. "It's one-upmanship, if you will," Graham said.
Meanwhile, Graham and company will try three approaches.
They will isolate canker-resistant genes found in hearty citrus plants such as kumquats, and they will "transport" those genes into the Florida orange and grapefruit varieties that are popular with consumers.
They will study canker-resistant citrus varieties in Brazil, where the disease has been prevalent since the 1960s, with an eye toward importing them to Florida.
And they will try to "genetically improve" Florida's oranges and grapefruits by inserting DNA from other living things that might fight off canker. One idea already in the works involves DNA from cows. Another plan is to take a serious look at what Brazil is doing with canker-resistant genes from a flesh-eating fly from South America.
Food that involves a flesh-eating fly faces obvious perception problems, Graham said. "But I've seen the results and they're convincing."
The trick in altering a citrus fruit's genetic makeup is to do it without affecting the properties that make it desirable, like sweetness and a certain firmness.
The research in Alachua and Lake Alfred is gaining steam with an infusion of cash last fall from Congress. Lawmakers gave millions to the tree-cutting program but figured it made sense to throw some money to long-term solutions as well.
Once scientists successfully test their theories in labs, the genetically altered plants they create must then be tested under growing conditions in groves, which can take years. And before the technology can be used, it faces at least six years of regulatory review by the U.S. Department of Agriculture, the Environmental Protection Agency and the Food and Drug Administration.
The estimated cost of regulatory approval is $6-million.
Both Graham and Gabriel were working on a cure for canker in the early 1990s when the state was declared canker-free. Regulators ordered the destruction of the scientists' cultures, effectively ending their research.
The scientists picked up again in the late 1990s after canker reappeared in Miami.
Had the research been allowed to continue, "we'd probably have a tree out there now that would be resistant," Gabriel said. "We were close."