Ladi Adaikwu's top-shelf merchandise is hidden in a mud-brick shed in a warren of narrow alleyways in Angwan-Dodo, a farming village close to Nigeria's capital city Abuja. The steel door is secured with a heavy padlock, and when she opens it, a shaft of light cuts through the damp darkness to reveal what looks like a knee-high pile of narrow, dirt-encrusted footballs.
But don't be fooled by their humble appearance: These are high-quality yams, and around here they're as good as gold.
Adaikwu stoops to pick one up, and holds it under the light. "This one is just like a healthy child," she says. "If you plant it, it will grow directly."
Although this West African country is the world's biggest producer and consumer of yams, the ones inside Adaikwu's shed are special. They are "seed yams," meant to be planted, not eaten. Not only that, they're guaranteed to be disease-free, a trait that's increasingly hard to find here. While a typical seed yam might sell for the equivalent of 25 cents, these can go for nearly $10.
Because of an unfortunate combination of economics, farming tradition and genetics, Nigeria's general supply of seed yams is riddled with disease, threatening a crop that is indispensable to the country's diet and economy. But a group of scientists think they've found a way to make good seed yams like Adaikwu's more widely available — and hopefully provide a bulwark against climate change for the country's small farmers.
Americans typically think of yams as the sweet orange root vegetables topped with marshmallows in a familiar Thanksgiving dish. But in Nigeria, the word refers to a different breed of tuber that's white, savory, and can be bigger than your arm. Rather than a holiday treat, they're the country's most important cash crop, worth nearly $14 billion annually.
One-third of Nigerians, nearly 60 million people, depend on yams as a main source of income. Yams are Nigeria's no. 1 source of dietary calories, eaten with most meals either fried, roasted or pounded into a paste. In some parts of Nigeria, a person who hasn't eaten yam in a day is said not to have eaten at all.
Yams are also central to the culture of some Nigerian societies.They're honored in annual festivals, bartered as marriage dowries, cloaked in superstition and are the measure of a household's social standing.
But in the past few years, Nigeria's yam yield has dropped to its lowest level in two decades, according to the United Nations, even though the area of land under cultivation is rapidly rising.
"For a large number of farmers, seed yam is a big problem," said Robert Aseidu, West Africa research director for the International Institute of Tropical Agriculture (IITA), a nonprofit research organization based in Nigeria. "It's only now that we're seeing how big a problem this could become."
The trouble stems from the way yam is grown by Nigeria's small farmers. New tubers grow directly from planted pieces of old ones, rather than from seed. Traditionally, farmers will set aside the more measly yams from each harvest to use as seed yams for the next season, and take the bigger ones away to eat or sell. Having a big enough harvest to be able to keep your own seed yams is a mark of a farmer's competence; buying them at the market is considered bad luck.
At the same time, yams are clonal, meaning that each tuber is genetically identical to its "parent." So farmers are essentially planting the same yam over and over again, with none of the routine genetic mutation that typically occurs between generations to help ward off pests and diseases. And because farmers tend to set aside the worst yams as parents, they're unintentionally practicing a kind of anti-Darwinian "survival of the scrawniest."
"When you have this recycling over so many years, then they keep accumulating pests and diseases, and then productivity keeps reducing until you get to a stage where it's no [longer] economical to plant anything," says Beatrice Aighewi, a yam specialist at IITA.
That cycle is reaching a crisis point, forcing a reconsideration of the longstanding stigma against buying seed yam. Adaikwu opened her business a few years ago to take advantage of the emerging market. She sources good seed yams from around the country and reproduces them in her field. One of her first big hits was a high-yielding, disease-resistant variety that earned the nickname "Mecca Approaches," because of a reputation that it could help farmers earn enough money to make the pilgrimage to Islam's most holy site.
"Even now, demand is very high and I can't supply everybody," Adaikwu says. "To get enough seed yam is hard."
Aighewi says the solution to Nigeria's seed yam crisis is to replicate businesses like Adaikwu's on a large scale. But there's not a single commercial producer of seed yam in the whole country.
Aighewi and her colleagues have developed a promising solution, known as "aeroponics," that aims to make it easy for seed companies to mass produce good seed yams at a low price point. They clean a small piece of yam in an anti-viral solution, then use cuttings from a vine grown from that piece to reproduce hundreds of disease-free, high-yielding seed yams like "Mecca Approaches." Aighewi says a few seed companies have already expressed interest in licensing the technology.
More and better seed yams wouldn't just help farmers now. They could also be important for adaptation to climate change, which is expected to increase drought and desertification in some parts of Nigeria where yam is most popular. Yam is much less sensitive to drought than other staples like maize; if there's not enough rain for them to grow, they're happy to wait underground until there is.
Inside Adaikwu's shed is another pile, this one full of virus-infected rejects. They are visibly malformed and covered with lumps. Without an intervention, seed yams like this could be the doom of Nigeria's farmers, she warns.
"When you have a seed yam that's not productive enough, you may plant several acres and still not get anything from it," she says. "So it's better that you go for a good seed yam, something that will let you eat, that you can sell."
Tim McDonnell is a Fulbright-National Geographic Fellow and multimedia journalist covering environmental issues in sub-Saharan Africa. You can find his work here, and follow him on Twitter @timmcdonnell.