Africa's cassava come back

"Mzee Hamis is a proud man. For half a century he fed his three wives and brought up 18 children on his 2-hectare plot on the island of Zanzibar in east Africa. His fields of cassava were his store cupboard, yielding food when other crops failed. Then one day, four years ago, the cupboard was bare. "The bushes looked healthy," he says. But when he dug them up to harvest the tubers, he found every last one had rotted away. "I had lost my entire crop. We were hungry and I was desperate.""