Good news for cassava as new varieties to combat deadly viral diseases are officially released in Tanzania


Four  new high-yielding cassava varieties that are tolerant to the deadly Cassava Brown Streak Disease (CBSD) and resistant to the equally devastating Cassava Mosaic Disease (CMD), were last week officially released in Tanzania, providing a ray of hope to the millions of small-scale farmers who depend on the crop for their food and income in sub-Saharan Africa. The two diseases have been spreading rapidly through the Great Lakes countries of eastern Africa from war-torn Democratic Republic of Congo to Rwanda, Burundi, Kenya, Uganda, Tanzania, Mozambique and Malawi, nearly reaching epidemic proportions as all the varieties grown by the farmers are susceptible.  These diseases represent the greatest threat to food security in the region as cassava is Africa’s second most important food crop after maize and provides more than half of the dietary calories for over half of the total rural and urban population in sub-Saharan Africa.   Spread through sharing of infected planting materials and by a vector, the whitefly, the diseases have caused an estimated 1 billion USD worth of damage to Africa’s cassava.  The already poor small-scale farmers bear the brunt of this loss.

The new varieties dubbed Pwani, Mkumba, Makutupora and Dodoma are a result of eight years of collaborative work between researchers from Tanzanian Agricultural Research Institutes (ARIs), the International Institute of Tropical Agriculture (IITA) and the International Centre for Tropical Agriculture (CIAT). They were developed through Molecular Marker Assisted Selection (MMAS) techniques that rely on advances in biotechnology to speed up the conventional breeding process. Aside from being disease resistant, the new varieties can easily double the crop’s production with their potentially high yields (23 – 51t/ha against the current average yield of 10t/ha). They also meet other local preferences such as taste, ease of cooking and texture. According to Dr. Geoffrey Mkamilo, the Team Leader of Cassava Research in Tanzania, the farmers will be very relieved and happy as they have been eagerly awaiting these varieties as the two diseases have devastated the crop’s production for many years. He points out CBSD as being especially devastating and causing a lot of heartbreak to farmers. “This disease has has been very devastating because its symptoms are not always clear. Farmers looking forward to a good harvest get a rude shock when they harvest and discover the useless rotten roots,” he explained. “As a result, many of them had abandoned this hardy crop that performs relatively well even under harsh conditions such as poor soils and little rainfall.”

The project was funded by the Rockefeller Foundation (RF) and the Alliance for a Green Revolution in Africa (AGRA). The Generation Challenge Program of the Consultative Group on International Agricultural Research Centers (CGIAR) contributed funds for farmer participatory trials to test for resistance and productivity under actual farm conditions and to complete tests required by the National Variety Release Committee before the new varieties could be officially released to farmers.Dr. Edward Kanju, a cassava breeder with IITA-Tanzania, who was also involved in the research, says that the varieties were developed by crossing local varieties with those introduced from Latin America from CIAT in Colombia and are the result of eight years of research. “We used local varieties from Tanzania as sources of resistance to CBSD and for local adaptation and those from CIAT as sources of high yield and resistance to CMD and cassava green mites,” he said.

CMD first appeared in Uganda in the mid-1980s, spreading fast across the region almost bringing cassava production to a halt. However, efforts by scientists from national and international research institutes with support from the donors and development agencies were successful and production started picking up again. Resistant and tolerant varieties – they give reasonable yields even when infected by the virus- were developed, multiplied extensively, and distributed to farmers. There was a lot of awareness creation on disease symptoms and measures to stop its spread. Then CBSD, which was historically found only in the coastal low altitude areas of eastern Africa and around Lake Malawi, struck. From 2004, it started spreading to mid-altitude areas leaving behind a wave of destruction and despair as all the varieties that were developed and resistant to CMD were susceptible to this disease sending the the scientists back to the drawing board.

The next challenge will be to get adequate planting material for farmers. At the moment, farmers mainly get their planting material from neighbours, Non-Governmental Organizations (NGOs) and the government, and supplies can be erratic. To address this, cassava stakeholders are seeking to develop systems to enhance production, sale and marketing of clean cassava planting material to supply demand both from small-scale as well as commercial cassava growers. The combination of these new varieties coupled with improved systems for delivering planting material offers huge promise for a brighter future for cassava in Tanzania and the region as a whole.

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