Some foods are known as seasonal wonders, making an appearance only once or twice a year when families gather for holiday feasts. Cranberry sauce, pecan pie, eggnog. Sweet potatoes, typically with tiny marshmallows roasted on top, were once on that list. But sweet potatoes are on the rise. They have become increasingly recognized as a superfood packed with essential vitamins and nutrients, and are now enjoyed throughout the year—in upscale restaurants, as a healthier alternative to French fries, and in products as varied as vodka, sausage and muffins.
Craig Yencho is crouching in a field of sweet potatoes in the remote northwest corner of Uganda, not far from a massive tent camp that is home to thousands of refugees from South Sudan. He has driven more than seven hours from Kampala, the country's chaotic capital city, across the Nile River and past a pack of wild baboons and a couple of wandering elephants to get to a research farm in the town of Arua. He is struggling with a stick to dig into the dirt, which has been baked rock hard by the unforgiving equatorial sun and the delayed onset of the rainy season. What he finally pulls out of the ground is a scrawny excuse for a sweet potato. It is also riddled with holes that are signs of weevils, a small but pervasive pest that can wipe out a crop.
Yencho, a William Neal Reynolds Distinguished Professor and leader of NC State's sweet potato and potato breeding and genetics program, was one of the masterminds behind Covington, the variety now grown throughout North Carolina. He also leads an effort, fueled by a $12 million grant from the Bill and Melinda Gates Foundation, to bring molecular science to sweet potato breeding programs in Uganda and a handful of other sub-Saharan countries in Africa. His ultimate goal is twofold — to use sweet potatoes to increase economic opportunities and to get sweet potatoes' nutrients into the bellies of children and pregnant women who suffer from such serious vitamin A deficiencies that they are in danger of going blind.
Sweet potatoes are already a staple of the diet for many families in Uganda, who eat them steamed in banana leaves or simply boiled, sometimes with every meal. But most of the sweet potatoes grown in Africa would be unfamiliar to American consumers. Instead of orange, they have white, cream-colored or yellow flesh, and are not as sweet or soft as their American cousins. They also don't have all the nutrients found in orange-fleshed sweet potatoes.
But changing consumer preferences may be the easy part of Yencho's challenge — early promotional efforts touting the health benefits of orange foods such as sweet potatoes and mangoes have created some converts. "Kids are attracted by the orange color," says Robert Mwanga '01, Ph.D, a Ugandan scientist who won the World Food Prize in 2016 for his pioneering work to promote orange-fleshed sweet potatoes in his country. "Also, the softer the food is, the better it is for kids. It's easier for them to eat."
The bigger challenge is breeding new varieties of orange-fleshed sweet potatoes that can be grown in Uganda. Weevils take advantage of dry, cracked soil brought on by drought (and a lack of irrigation) to burrow their way into growing sweet potatoes, and wipe out more than 70 percent of the crop in most years. "Everywhere that sweet potato is grown [in Uganda], you will find weevils," says Mwanga. And orange-fleshed sweet potatoes, which typically have less starch and are therefore less dense than most of the sweet potatoes grown in Uganda, are softer and easier for weevils to burrow into. "We still have a long way to go," Mwanga says, "to get something that farmers can leave out in the field and not worry about the weevil."
As insurmountable as the challenges may seem, Yencho is undaunted. He laughs when he is asked during a visit to Uganda and Kenya last year if it feels like he is forever pushing a heavy rock up a steep hill, like a modern-day, gray-haired Sisyphus. "Yeah, it can feel like that sometimes," he says. But Yencho prefers a different outlook, one that reflects an optimism dating back to his wanderlust days as a young Peace Corps volunteer in St. Kitts and Nevis.