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diseases have been a problem for about 100 years. particularly bad virus is
cassava brown streak disease. It infecting cassava fields in East Africa 10 years ago. it has spread as far west as the Democratic of Congo. Brown streak disease is spread in two : by white flies and by infected stem cuttings. Farmers these cuttings instead of seeds to plant their fields. Fauquet is a plant virus expert. He heads the Cassava Partnership for the 21st Century. He says it hard to see signs of the disease in the itself. Instead, it becomes visible in the roots when plant is harvested. He says scientists and organizations have find a way to offer farmers virus-free plant cuttings. Fauquet says scientists are experimenting with a virus-resistant cassava in Tanzania. Experts warn that brown streak disease could cassava production in Africa by 50 percent. For VOA English, I'm Mario Ritter.