CMD has been damaging farmers’ fields across Africa for decades. Over the last 15 years, CBSD has also spread rapidly and now affects cassava production across East and Central Africa. It threatens to move into West Africa where it would have devastating effects on cassava production and food security in Nigeria, Africa’s most populous country and largest cassava producer. As a result, CBSD has been defined as one of the seven most dangerous plant diseases in the world due to its ongoing and potential impact on food and economic security.
Conventional plant breeding has been used successfully to develop cassava varieties that are resistant to CMD. But plant breeders have been less successful with CBSD, thus far developing varieties that are merely tolerant to the disease. CBSD tolerant cassava plants may still show some virus symptoms and suffer damage from the disease – and may cause the disease to spread further.
Our work: developing cassava varieties that will be resistant to both Cassava Brown Streak Disease (CBSD) and Cassava Mosaic Disease (CMD)
Our researchers are using genetic engineering to introduce a small component of the Cassava Brown Streak Virus into cassava to make the plants resistant to CBSD by a mechanism called RNA interference (RNAi). RNAi has been used to develop a number of disease resistant crops, most notably saving the papaya industry in Hawaii from the devastating Papaya Ringspot Virus Disease.
We have successfully developed cassava with strong and stable resistance to CBSD using genetic modification techniques and conducted several confined field trials in both Uganda and Kenya, with the approval, oversight and guidance of government regulators. The Kenya Agricultural and Livestock Research Organization (KALRO) has submitted an application to the National Biosafety Authority (NBA) for environmental release and placing on the market of cassava that is resistant to CBSD (read more).
Cassava varieties that are resistant to CMD have already been developed using conventional plant breeding, so additional breeding work will combine those CMD resistant varieties with transgenic CBSD resistance. Field development and testing of these new varieties is ongoing in Kenya and Uganda to ensure that they control both plant diseases while producing good yields and maintain farmer preferences for taste, texture, processing and storage practices.
When both cassava virus disease resistance traits are combined and bred into VIRCA Plus varieties, and fully assessed for safety, farmers will be able to grow cassava with specific resistance to both diseases for the first time. Kenya, Uganda and other East African countries are expected to be the initial markets for disease resistant VIRCA Plus varieties.