Agricultural experts are optimistic about three cassava varieties that have shown promise against the dual threat of the cassava brown streak disease (CBSD) and cassava mosaic disease (CMD) in crop trials in Uganda. The varieties offer hope to millions of poor cassava farmers in the mid-altitude areas of eastern and central Africa whose morale - and livelihoods - have been severely dampened by the two diseases.  

Dr Edward Kanju, a cassava breeder with the International Institute of Tropical Agriculture (IITA) and one of the scientists behind the work, says he is happy with the "promising three" that have not only shown very mild symptoms of the diseases but are also very productive. 

The researchers are readying to move the varieties from on-station experimental plots to the fields to test their tolerance and productivity under actual farm conditions before they can be officially released to the farmers. In the meantime, IITA and its partners continue to search for varieties that are truly resistant to both viral diseases. 

Kanju says that  the three were selected from among 14 breeding lines that showed resistance to CMD and CBSD from last year's growing season. The three showed mild symptoms, mostly only on the leaves. The roots - the most economically important part of cassava-remained untouched. They also produced up to 35 tonnes of the crop per hectare, which is more than triple Uganda's average of 10 tonnes per hectare.

The group will start another breeding cycle soon, crossing the varieties with locally adapted ones to transfer the tolerant genes. They would also try to identify other sources of resistance to complement the breeding work.

"We will also provide the promising varieties to our partners in Kenya, Malawi,Tanzania, Rwanda, and the DRC - countries already suffering from or immediately threatened by the diseases - so they could carry out their own breeding trials adapted to local conditions," he says.  

The research, initiated in 2004, is funded by IITA and being carried out in collaboration with the National Agricultural Research Organization (NARO) of Uganda. It focuses on CBSD that causes a dry rot in cassava. The disease has been around in eastern and central Africa since the 1930's but confined to the low altitude coastal lowlands. However in 2004, a deadlier form of the disease was reported in Uganda, spreading to the mid-altitude areas of neighbouring countries that are just recovering from bouts with CMD.

The team admits that it might take a few more years before cassava farmers get hold of varieties that are truly resistant to both diseases. Kanju emphasizes that farmers should look forward to this.

"Truly resistant varieties that have internal mechanisms that either stop the virus from spreading within the plant or keep its population so low that it cannot easily infect nearby plants, are the most sustainable and cost-effective solution to these deadly diseases," Kanju concludes.

Courtesy: IITA