IITA scientists are a step closer to making a breakthrough in developing cassava that is resistant to both the Cassava Brown Streak Disease (CBSD) and the Cassava Mosaic Disease (CMD) in Eastern and Central Africa. The two diseases are the greatest threats to cassava production in the region putting at risk the food security and livelihoods of over 200 million people.
According to Edward Kanju, IITA cassava breeder, there are 14 types of the crop under research that are very promising. Kanju’s team had just harvested an advanced trial of such cassava in Ug anda.
“I am very excited with the results of the trials,” he said. “Eight out of the 40 types of cassava under trial did not show any disease symptoms, while 6 had only very mild symptoms either on the roots or leaves or both.”
The next step, he said, will be to subject these varieties to even more pressure by deliberately grafting them with diseased plants. “This is a very severe test for establishing disease resistance, and if they still do not show any signs of the diseases, then we can confidently, and for the first time, say that we indeed have cassava varieties that are resistant to both CBSD and CMD,” he emphasized. “These can then be used for breeding for resistance in other countries in the Great Lakes region such as Rw anda, Tanzania, Kenya, and DR Congo.”
According to Kanju, this is the fourth year of trials for dual-resistance cassava for mid-altitudes in Ug anda. The trials are being conducted at Mukono, near Kampala, an area regarded as a hot spot for CBSD and CMD. The breeding work started with over 5000 true seeds of parents with tolerance to CBSD from Tanzania that were sent to Ug anda for crossing with IITA varieties that are resistant to CMD.
Before 2004, CBSD was found only in the coastal areas of Eastern Africa and around Lake Malawi. However, the disease, which causes a dry rot in the roots rendering them inedible, started spreading to mid-altitude areas. The disease has drastically affected cassava production in Central and South-Western Ug anda, North Western Tanzania, Western Kenya, and North Western DR Congo. Tolerant varieties for the coastal low altitudes were developed by IITA and its partners, and released in Zanzibar in 2007.
CMD, on the other h and, first appeared in Ug anda in the mid-1980s, spreading fast across the region and almost bringing cassava production to a halt. IITA researchers and partners have since developed resistant varieties, but these are now threatened by new strains of the disease. CMD causes annual yield losses of 34 million tonnes in Africa, approximately a third of total production; while losses from CBSD are less well documented but it has been known to cause 20-80 per cent yield reduction as it affects the roots and leaves, the most useful parts of the crop.
The cassava grown from the Tanzanian seeds have been repeatedly subjected to high disease pressure along with susceptible varieties for comparison. From each growing season, only 10 per cent of the cassava were selected for the next stage. “After four growing seasons,” Kanju says, “we are down to 14 promising varieties.”
Farmers have also been involved in the selection process to ensure that the varieties meet farmers’ preferences on cooking taste, texture, and yield. Breeding for dual-resistance cassava is also being conducted in Tanzania and DR Congo.
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For more information, please contact:
Dr Edward Kanju, e.kanju@cgiar.org
Cassava Breeder
IITA-Tanzania
Tel. +255 22 2700092
Catherine Njuguna, c.njuguna@cgiar.org
Corporate Communications Officer (Eastern and Southern Africa)
IITA-Tanzania
Tel. +255 22 2700092
Jeffrey Oliver, o.jeffrey@cgiar.org
Corporate Communications Officer (International)
Communication Office
IITA – Headquarters
Ibadan, Nigeria
Tel. +234 2 7517472
URL: www.iita.org
About IITA
Africa has complex problems that plague agriculture and people’s lives. We develop agricultural solutions with our partners to tackle hunger and poverty. Our award winning research for development (R4D) is based on focused, authoritative thinking anchored on the development needs of sub-Saharan Africa. We work with partners in Africa and beyond to reduce producer and consumer risks, enhance crop quality and productivity, and generate wealth from agriculture. IITA is an international non-profit R4D organization since 1967, governed by a Board of Trustees, and supported primarily by the CGIAR.
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