Sweet Potato Scientist: Chris Clark devotes career to better production, higher yields

Linda Benedict, Clark, Christopher A., Gautreaux, Craig  |  6/10/2009 3:13:13 AM

There was a time in Chris Clark’s life that sweet potatoes made a one-time annual appearance – the Thanksgiving table. Little did he know that this delicious, nutritious menu item would help define his career. Since arriving at LSU in 1977, Clark has played an integral role in the development of sweet potato varieties that have kept the Louisiana industry viable.

Clark grew up in upstate New York where summers were spent assisting researchers with their cabbage and bean projects at the New York State Experiment Station. He later attended Cornell University earning three degrees.

It was his one-year, post-doctoral assignment that started his trek south. "It was a cotton research program in North Carolina, and it was my introduction into large-scale one-crop agriculture production," Clark said.

His next stop took him farther south into Louisiana where he was exposed to sweet potatoes. It was not the best time to be involved with them, according to Clark. "I got off to a slow start. It rained for 54 consecutive days. I can still remember the haunting aroma of rotting sweet potatoes," Clark said.

When Clark came to Louisiana, sweet potatoes were grown on nearly 30,000 acres. Today, that number has been reduced to approximately 15,000 acres. Although acreage has decreased significantly, higher-yielding varieties have kept sweet potatoes profitable for growers.

"When I first arrived in Louisiana, Centennial was the dominant variety. It was replaced for a short time by a North Carolina variety called Jewel. Unfortunately, this variety was susceptible to flooding, which is a major concern in Louisiana," Clark said.

The Louisiana sweet potato industry was at a crossroads. Growers needed a variety that had a high yield, was disease-resistant and had a consistent shape, look and taste.

Fortunately, scientists with the LSU AgCenter were about to unleash the magic bullet, a variety that would revolutionize the growing of sweet potatoes across the country.

In 1987, Beauregard was released, and its effect on the Louisiana sweet potato industry was enormous. "Prior to Beauregard’s release, the sweet potato industry was about a $25 million industry," Clark said. "After the release of Beauregard, it jumped back up shortly afterward into the neighborhood of $150 million."

The variety performed well in other states and soon became the dominant variety in the industry. Beauregard was hailed as being a savior by farmers across the country and at its peak would account for nearly 80 percent of the nation’s acreage.

"Beauregard was such a success that growers felt confident enough to build new storage and packing facilities," Clark said.

The development of a crop variety requires a team of many disciplines. Plant breeders, entomologists and weed scientists all play a critical role. Clark serves as the team’s plant pathologist. In 2008, Clark was selected as the LSU AgCenter’s top scientist of the year and was presented the Doyle Chambers Research Award.

"The LSU AgCenter’s sweet potato research team, of which Dr. Clark is part, has been recognized for its excellence by receiving the Tipton Team Award from the Louisiana Agricultural Experiment Station in 2002," said David Boethel, LSU AgCenter vice chancellor for research.

"Diseases are a limiting factor in production, and Dr. Clark’s research has led to the virus-tested seed program, and the management of other diseases has been instrumental in sustaining the sweet potato industry in Louisiana and other southern states," Boethel said.

Clark’s primary task is to develop seed plants free from viruses. "Viruses tend to accumulate in the planting material, so we have to go through special efforts to get rid of them so growers have clean material to plant," Clark said.

Viruses can reduce yields up to 30 percent and affect the quality of the sweet potato. Through the AgCenter’s virus-tested seed program, growers now have a reliable source for seed.

Searching for a variety resistant to a specific disease can be a long and arduous task. "People began looking for soil-rot resistance in 1908. It took them to about 1977 before the first variety was released, which was Jasper," Clark said.

Clark says he screens for eight primary diseases when examining varieties for potential release. The variety does not have to show resistance to all of the diseases, but it should have a disease package that would be of benefit to growers. Although finding the right resistance package takes hard work and much testing, it can be serendipitous.

For example, Fusarium wilt is a disease that can cause significant losses. According to Clark, a line of sweet potatoes resistant to this disease was found insweet potato on the island of Tinian that he liked," Clark said, "and it turned out it was resistant to Fusarium wilt."

This South Pacific sweet potato then became part of breeding programs across the country to help overcome Fusarium wilt. Clark says this is a prime example of how difficult it can be to find a source of disease-resistant plant material.

Unfortunately for Clark and his colleagues, sweet potatoes mutate quite frequently and are susceptible to pathogens. One characteristic that often reveals a mutation is a change in the color of the flesh. Often, a lighter color flesh will appear. A lighter flesh sweet potato will present problems because consumers seek a richer orange, uniform color.

Travel is often part of Clark’s quest to find a resistant line. He has visited China in hopes of finding a line resistant to some of the common diseases found in this country. Clark estimates that 80 percent of the world’s sweet potatoes are produced in China. Clark says that the eastern part of Africa is another region important for both sweet potato production and research.

Worldwide, sweet potatoes are seen as a "poor man’s crop." "Sweet potatoes have helped people survive during difficult times. Examples in America include the Great Depression and World War II," Clark said.

In developing countries, sweet potatoes are prized because of their ability to grow in poor soils and in small areas. Clark says that in some parts of the world sweet potatoes are grown between the road and the sidewalks that border them.

Clark says that the LSU AgCenter’s latest sweet potato release, Evangeline, is showing much promise. "It’s been judged sweeter than Beauregard, and its darker orange color makes for a better appearance," Clark said.
 
Its yield is comparable to Beauregard, but it is more susceptible to a fungus problem. Clark says that the team is looking at alternative fungicides and treatment plans to better manage this issue. He suspects that Evangeline will eventually overtake Beauregard as the dominant variety in Louisiana.

Convincing people that sweet potatoes are not just food for the holidays is one area of marketing that can be improved. Clark had to sell this very idea to his own family. His daughter proudly proclaimed not to be a fan of the root, but now as a physician, she recognizes the health benefits that sweet potatoes provide. Sweet potatoes are a good source of beta carotene and folic acid and are better for diabetics than other types of potatoes.

Chris Clark has made a career with sweet potatoes. And these days they appear quite often on the menu at the Clark household.

Craig Gautreaux

(This article was published in the spring 2009 issue of Louisiana Agriculture.)

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