A 'Sweet' Fuel Source

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Dr. Craig Yencho has created sweet potato hybrids with ethanol potentials comparable to that of corn.

By Keith Nichols, News Services

It came from the bottom of the sea and attacked... the problem of creating a sustainable biofuel?

This is no science-fiction story. NC State researchers Drs. Craig Yencho and Bryon Sosinski want to cultivate sweet potatoes that are white inside and out, bulbous, overly starchy and contain genes from deep-sea bacteria. These are industrial sweet potatoes, not the ones you put in your sweet potato pie.

Enzymes produced in deep-sea thermal vents could help the industrial sweet potato convert practically all of their starch into simple sugars that can then be processed into ethanol. Even without the extra help, sweet potatoes hold the potential for ethanol production.

"Sweet potatoes are capable of producing tremendous amounts of biomass, mostly starch-based," Yencho said. There is also a tremendous amount of them around the state -- North Carolina grows about 40 percent of the U.S. food crop and could do equally well with the industrial variety sweet potato.

Using plants from China, Africa and South America, Yencho has created hybrids with starch contents more than 50 percent higher than the sweet potatoes most Americans eat. More starch means more sugars that can be fermented into ethanol. At that level, the sweet potato's ethanol potential becomes comparable to that of corn.

Yes, there's a catch. Producing an acre of sweet potatoes costs about 10 times the cost of producing an acre of corn. So Yencho and Sosinski are studying ways to cut production costs.

Sweet potatoes are usually planted by hand using transplants.

"But if we could plant them the same way you plant an Irish potato - using cut 'seed pieces' and mechanically putting them into the ground - we could cut planting costs in half," Yencho said. "The ethanol production from sweet potatoes then becomes much more cost effective and feasible.

"Not only would these sweet potatoes be a much more viable ethanol source," he said, "but because they are industrial sweet potatoes, we wouldn't be taking away from a food source, which is a potential problem with corn."

Sosinski is now growing modified sweet potato seedlings - that include deep-sea genes - in the lab. He hopes to move into greenhouse trials this year and into field plantings within two to three years.

By then, Sosinski and Yencho are hoping that equipment and mechanization processes will catch up, making the sweet potato - and North Carolina - a giant among ethanol producers.