During the past decade, Cassava mosaic disease CMD has been the focus of extensive collaborative research to understand the nature of the disease and to develop resistant varieties of cassava. However, another disease, although currently confined to the East African coast, can render susceptible varieties unusable if cassava roots are left in the ground for over nine months. Like CMD, Cassava Brown Streak Disease CBSD is a viral disease. But, unlike the mosaic symptoms of CMD, the foliar symptoms of CBSD are less conspicuous and farmers are often unaware of the problem until the crop is harvested and the corky, yellowbrown necrosis affecting the roots becomes evident. As a twoway approach to controlling the disease, scientists at NRI and the University of Bristol in the UK, through the DFIDfunded Crop Protection Programme, are working to identify the virus and its vector and to produce virusfree material for distribution to farmers.

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