Transgenic tomato withstands bacterial spot, yields more fruit

10/08/2012 01:11:00 PM
Vicky Boyd

transgenic tomatoesCourtesy Two Blades FoundationThe tomatoes to the left are the Fla. 8314 variety into which the Bs2 bacterial spot-resistance gene has been inserted. The tomatoes to the right are VF 36, which is extremely susceptible to bacterial spot. When a gene from bell and hot peppers is inserted into tomatoes, it not only imparts resistance to bacterial spot—a devastating tomato disease—it also bumps up yields.

Jay Scott, a University of Florida tomato breeder at the Gulf Coast Research and Education Center in Wimauma, admits a small segment of the population opposes transgenic crops.

But he says the benefits of a bacterial spot-resistant tomato to the environment and growers would be a strong selling point.

“We still have to overcome different views on transgenic crops,” he told attendees of the recent Florida Tomato Institute in Naples. “My personal feeling is most people just don’t care.

“We need to emphasize to the public that this is a green technology. We’re using less pesticide and putting less contaminant into the environment.”

Transgenic tomatoes are nothing new. The now-defunct Davis, Calif.-based Calgene introduced the first transgenic crop—the Flavr Savr tomato under the MacGregor’s label—in the 1990s.

Because of shortcomings with the trait, Flavr Savr tomatoes never took off, Scott says.

But consumers back then actually wanted the tomato because it was genetically engineered, he says.

“If it was successful, we might have a different attitude today,” Scott says.

The need for disease control

Growers apply an average of $500 worth of copper and mancozeb annually to try to control bacterial spot—one of the most devastating tomato diseases along the East Coast—without much success.

Statewide, tomato growers spend about $28 million on copper and $14 million on mancozeb annually to fight the problem, he says.

Gary Vallad, assistant plant pathology professor at the Gulf Coast center, has conducted numerous field trials to try to find effective bacterial spot controls. Outside of streptomycin, an antibiotic not registered for field-grown tomatoes, nothing has stood out.

Even then, antibiotics provide at best 85 percent control and no significant yield improvement, he says.

Actigard, an SAR—or systemic acquired resistance—product produces at best a 35 percent reduction in bacterial spot symptoms. But it does little to improve yields, Vallad says.

Copper, the industry mainstay, is relatively ineffective since most strains of Xanthomonas—the organism responsible for bacterial spot—have grown resistant to it, he says.

Copper also has come under fire because it can build up in the soil to toxic levels.

Helping Mother Nature

For the past 30 years, Scott and other tomato breeders have been unsuccessful in developing a bacterial spot-resistance tomato using conventional breeding techniques.

As a breeder, Scott says he looked for better resistance in related tomato species.

Finding none, he then looked to a gene, known as Bs2, found in many bell and hot peppers that is responsible for bacterial spot resistance.

Although peppers and tomatoes are both members of the Solanaceae family, they won’t crossbreed.

So Scott, in cooperation with UF plant pathologists Bob Stall and Jeff Jones, started testing transgenics that had the Bs2 gene from peppers transferred into tomatoes.

Researchers in Brian Staskawicz’s laboratory, University of California, Berkeley, made the original transformation, inserting the Bs2 gene into VF 36, an old California variety that is highly susceptible to bacterial spot.

Scott’s trials in Balm showed the transformed variety not only withstood bacterial spot with few symptoms, but it yielded significantly more than its conventional counterpart.

The conventional California variety, on the other hand, had about 80 percent infection.

The Bs2 gene was then inserted into Fla. 8000, a parent of the Florida-adapted hybrid Fla. 8314. And the Fla. 8000 Bs2 parent was used to develop FL 8314 with the Bs2 gene.

Two seasons of field trials have yielded results even surprising Scott.

“The yields are essentially double, which is quite remarkable,” he says. “Same for the extra large yield.

“I don’t know a single thing that is wrong with [the gene} where it does something bad in tomatoes. I haven’t seen anything that affects yield, firmness or marketability.”

They were compared to conventional counterparts, which had high rates of bacterial spot infection and much lower yields.

Scott says he’s noticed that the transgenic tomatoes also had less early blight infection in recent replicated trials.

The reason for this unexpected result is not known, but he says it might be that the lack of bacterial spot damage makes it more difficult for the early blight fungus to attack the plants.

Growing tomatoes without copper applications would free producers from a burdensome disease and allow them to improve integrated pest management efforts toward other diseases, Vallad says.

The next step

Scott’s work is supported in part by the Evanston, Ill.-based Two Blades Foundation, a nonprofit group that supports development of durable disease resistance in plants, particularly for subsistence farmers.

The group typically underwrites research through the proof-of-concept stage.

In this case, the proof was a paper Scott co-authored that was published in the Aug. 1 issue of the peer-reviewed journal, PLoS ONE.

The next step will be for a company, a grower group or some other entity to step forward and help fund moving the Bs2 tomato through the deregulation process, says Diana Horvath, Two Blades chief operating officer.

Transgenic crops are regulated by the Environmental Protection Agency, the Food and Drug Administration and the U.S. Department of Agriculture.

The agencies require additional testing to show the crop is safe to consumers, non-target species and the environment.

Because the Bs2 tomato has not been deregulated, Scott must adhere to strict regulations, and all crop material must be destroyed at the end.

The goal would be for the agencies to rule that the transgenic tomato is not materially different in composition, safety or other components than a non-transformed tomato.

The deregulated status would allow the Bs2 tomato to be grown and marketed without restrictions or added requirements, such as labeling.

Both Horvath and Scott say they don’t believe bringing the transgenic tomato to market will be a problem.

“Jay’s talk has generated a lot of interest,” Horvath says. “We’re confident we’ll be able to put together the funding to get the deregulation done. Whoever pays the money for the deregulation will control the asset and what happens to it.”

Because of Two Blades’ humanitarian mission, Horvath says the technology would be provided free to subsistence farmers worldwide.

She says they’re also looking for grower-cooperators who would like to plant and test a small plot of the transgenic variety.



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Pedro Pompeyo Osores Morante    
Peru  |  September, 14, 2012 at 10:37 AM

The chemicals companies are wrong the transgenic crops will makes resistance by acelered mutations in diseases like Bt transgenic,Cry transgenic and others cases With propaganda campaign only whant win time for a bisness of 50 billion dolars its falling down around the world

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