Bruce Fortnum inspecting the guide belt on
a modified tobacco harvester.

DATE: 11/2/2005

CONTACT: Dr. Bruce Fortnum, (843) 662-3526; bfrtnm@clemson.edu

WRITER: Tom Lollis, (803) 284-3343, ext. 241; tlollis@clemson.edu

Clemson scientists modify tobacco equipment to combat wilt spread

FLORENCE – What do bananas have to do with helping South Carolina tobacco growers combat a multi-million dollar problem with bacterial wilt disease?

Bacterial wilt, once a minor problem in this state, can knock out as much as 8 percent of the state’s flue-cured tobacco, which is worth more than $100 million annually, according to Bruce Fortnum, Clemson University tobacco plant pathologist at the Pee Dee Research and Education Center.

In 2000 Fortnum attended a meeting in Guadeloupe in the French West Indies, where he spoke to a scientist from Africa who worked on bacterial wilt in bananas.

“He told me that when they harvest bananas, they have to sterilize their knives before cutting each bunch,” he said. “If they don’t, they will spread the disease and kill the whole plantation. They put dyes in their sterilizing solutions so they can see it on the stump. If they don’t see the dye, they fire the harvesting crew.”

Fortnum figured that cutting a banana bunch is not a lot different from cutting the flower off the top of a tobacco plant to encourage leaf production rather than seeds. After the Guadeloupe meeting he conducted an experiment at the Pee Dee REC in two rows of tobacco planted side by side.

He inoculated the first plant in each row with the bacterium that causes wilt. Then he topped one row by hand and used a machine topper in the other. A month after the topping, all the machine-topped plants had collapsed from bacterial wilt.

“That let us know that machine transmission of the disease is very possible,” said Fortnum.

“This state was pretty much free of bacterial wilt until the late 70s,” said Bruce Fortnum, Clemson tobacco plant pathologist at the Pee Dee Research and Education Center. “Losses were maybe two-tenths of one percent.”

He attributes the increase in wilt to a change in production practices.

“We missed bacterial wilt at Pee Dee REC because we top and harvest our tobacco by hand the way growers did 30 years ago, since we have short plots,” said Fortnum. “A large farm, when I first came to Clemson in the late 70s, was 20 acres. Now growers have five times the acreage so they will have the economic unit needed to stay in business. The only way to handle that is to use machinery.”

With that machinery farmers spread bacterial wilt from tobacco plant to tobacco plant and from field to field.

Fortnum and Extension tobacco specialist DeWitt Gooden have worked with Clemson agricultural engineer Roy Dodd and topping equipment patent holders in North Carolina to design a new system that will allow sterilization of the blades that remove the tobacco flower.

“We have a prototype, which we used this season,” said Fortnum. “It’s very effective. We can get about 90 percent control. With Roy, we’re refining the design to prevent stalk injury and make it more usable.”

The topper prototype will be in the hands of a limited number of farmers in South Carolina and North Carolina in 2006. He’s not certain when kits, which should be relatively inexpensive, will be available to tobacco growers.

Harvesting equipment also spreads bacterial wilt. At the bottom of the harvester, stiff rubber guide bars funnel the stalk through the machine as leaves are stripped from the plant. The bars abrade the stalk, cutting through the outer fiber into the vascular tissue, picking up disease inoculum which can be passed on to the rest of the field.

“We’ve reengineered that guiding system to use a soft belt that moves on rollers, staying with the stem as it passes through the machine so that we no longer get the abrasion,” said Fortnum. Disinfectants such as chlorine bleach solutions are applied to the belt to kill bacteria.

“We had lower incidence of disease this year in plots where we used the new design,” he said.

“We are in conversation with tobacco harvester manufacturers about refitting kits that could be bolted onto a farmer’s tobacco harvester,” he said.

Fortnum said that machinery which does not spread plant pathogens will become even more critical over the next decade as producers have the opportunity to grow tobacco that has been genetically engineered to produce medical proteins.

Drug manufacturers are already producing materials such as human interferon, human growth hormone, human serum albumen and some cancer-fighting drugs in fermentation systems using engineered cell culture.

“You can produce much larger quantities of those substances with tobacco, which is easy to engineer,” said Fortnum. “Doubling production is as simple as planting 100 acres instead of 50. You don’t have to build more fermentation systems that cost millions and millions of dollars.”

Tobacco for pharmaceutical purposes won’t replace the acreage grown for smoking leaf.

“It will be small acreage, but very, very high value,” he said.

Fortnum, Gooden and entomologist Albert Johnson grew some transgenic tobacco at the Pee Dee REC this year.

“Some of the early products may go into the veterinary field because regulations will be less stringent than what would be required for products intended for human use,” Fortnum said.

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