Standing in a Tanzanian field, Christina Mwinjipe stares at a cassava plant that has been destroyed by brown streak disease.
As 200 million African farmers depend on the crop, better known in the West as tapioca, this disease could exacerbate problems of hunger and malnutrition on the continent. Together with cassava mosaic, it causes more than $1 billion of damage a year. For Mwinjipe, this means eating into her savings to buy cassava to feed her three children.
Fortunately, help is at hand in the unlikely form of Microsoft billionaire Bill Gates. The Bill & Melinda Gates Foundation is spending $1.2 million on research into tackling the viruses that attack cassava.