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A cassava plant usually reaches 3 to 4 feet in height, though some plants can grow up to 13 feet tall.

COLUMBUS, Ohio – Cassava is the third-most important food source in tropical countries, but it has one major problem: The roots and leaves of poorly processed cassava plants contain a substance that, when eaten, can trigger the production of cyanide.

Richard Sayre

That’s a serious problem for the 500 million people who rely on cassava as their main source of calories, among them subsistence farmers in Sub-Saharan Africa, saidRichard Sayre, a professor ofplant biology at Ohio State University. He and his colleague Dimuth Siritunga, a postdoctoral researcher in plant biology at the university, have created cyanogen-free cassava plants. A cyanogen is a substance that induces cyanide production.

Their study appeared in a recent issue of the journal Planta.

Cassava is a hardy plant – it can remain in the ground for up to two years and needs relatively little water to survive. It’s the key source of carbohydrates for subsistence farmers in Africa. But an unprocessed cassava plant contains potentially toxic levels of a cyanogen called linamarin.

The proper processing of cassava – drying, soaking in water, rinsing or baking – effectively reduces cassava’s linamarin content. But, said Sayre, shortcut processing techniques, which are frequently used during famines, can yield toxic food products.

“If we could eliminate the cyanogens in cassava, the plant wouldn’t need to be processed before it’s eaten,” he said. “In Africa, improperly processed cassava is a major problem. It’s associated with a number of cyanide-related health disorders, particularly among people who are already malnourished.”

Chronic, low-level cyanide exposure is associated with the development of goiter and with tropical ataxic neuropathy, a nerve-damaging disorder that renders a person unsteady and uncoordinated. Severe cyanide poisoning, particularly during famines, is associated with outbreaks of a debilitating, irreversible paralytic disorder called Konzo and, in some cases, death. The incidence of Konzo and tropical ataxic neuropathy can be as high as 3 percent in some areas.

People who get little or no protein in their diets are particularly susceptible to cyanide poisoning, as they lack the proper amino acids necessary to help detoxify the poison.