Cassava brown streak virus disease (Potyvirus - Potyviridae)
It is particularly serious in coastal areas of Kenya, Zanzibar, Mozambique and Tanzania and lakeshore region of Malawi and in Uganda and is a threat to the whole of sub-Saharan Africa.
The virus is vectored by whiteflies (Bemisia spp.) and also transmitted through infected cuttings. Symptoms include yellowing (leaf chlorosis) and brown streaks in the stem bark (cortex). Infected tubers have brown streaks (root necrosis) (Field Crops Technical Handbook, MoA, Kenya). It's a stealth virus, which destroys everything in the field. The leaves may appear healthy even when the roots have rotted away.
- Use diseased-free cuttings.
- Use tolerant/resistant varieties (e.g. "5543/156", "TMS 30572")
- Remove diseased plants from the field.