Case study 3: Hybrid Cassava and Cassava Mosaic Disease in Uganda

A local variety of cassava showing signs of African Cassava Mosaic Virus. Credit IITA

A local variety of cassava showing signs of African Cassava Mosaic Virus. Credit IITA

Cassava is grown in more than 40 countries in sub-Saharan Africa and Nigeria is now the largest producer of cassava in the world. Cassava production in Africa, however, is severely threatened by cassava mosaic disease (CMD). In the 1970’s the International Institute of Tropical Agriculture (IITA) developed high yielding mosaic disease resistant cassava varieties by a process known as ‘Tropical Manjioc Selection’ (TMS) that draws on earlier approaches crossing the disease resistant Ceara rubber x cassava hybrid with high-yielding West African selections.[1] These TMS varieties increased cassava yields by 40% without the use of fertiliser.[2]

In the mid-1990’s CMD appeared in a new, more virulent form in Uganda known as East African cassava mosaic virus. The epidemic spread south along a broad “front” at a rate of approximately 20 km per year subsequently reaching neighbouring countries and beyond. CMD is not only highly contagious, but the symptoms are severe. Infected crops in Uganda suffered a 55%-87% yield loss and in just 6 years, 80% of Uganda’s cassava crop was destroyed. Cassava was all-but abandoned in Uganda, contributing to food insecurity in the late 1990s.[3]

IITA, the National Root Crops Research Institute and the Root and Tuber Expansion Program have undertaken a project to conduct both demonstrations and on-farm trials in Uganda and Nigeria. From more than 2,500 trials, 12 disease resistant TMS varieties have been released. These have multiple resistance and tolerance to CMD along with other yield-damaging pests such as bacterial blight disease, anthracnose disease, green mite and mealybug. They are high-yielding and suitable for the food industry and livestock feed. Yields of these TMS hybrids range from 20 tonnes to 50 tonnes per hectare or 40% to 100% higher than local varieties.[4]

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