About eight hundred million people in Africa, Asia and South America eat cassava. The plant is a major source of food energy and a major food security crop. It cansurvive in poor soil and without much water. Also, the root can stay in the ground for as long as three years, so it can be harvested as needed.

But in East Africa the plant is under attack. Cassava brown streak disease is a moredestructive form of cassava mosaic. The mosaic has been active in East Africa for about one hundred years. It limits plant growth. But brown streak can destroy a crop. The virus was identified in Uganda in two thousand four and has spread fast in areas extending from Lake Victoria.