MAPUTO, Mozambique -- When U2's Bono broke into the classic refrain, "Gabba gabba hey!" from the Ramone's "Pinhead" on a Mozambique sweet potato farm last year, the farmers joined in to create perhaps the most unlikely punk rock cover of all time. Bono's riff was inspired by one variety of the vegetable called "Gaba Gaba."

In the last decade, the sweet potato has become an unsung hero in the fight against hunger and malnutrition in Africa. High in vitamin A and suited to a variety of climates, the sweet potato is championed by advocates of biofortification, a movement to improve global health...