STEALTH VIRUS

NEW SCIENTIST (April 21) described how a farmer in Zanzibar, had a severe shock four years ago when he went to harvest his cassava (manioc). “The bushes looked healthy” he said, but when he dug up the tubers he found every last one had rotted away. “I had lost my entire crop. And we were hungry and I was desperate”.

What he didn’t know then was that his crop was the first known victim of a plague caused by a new and virulent strain of the ‘cassava brown streak virus’ that is now spreading across eastern and central Africa. Other pests and viruses that afflict cassava – notably the ‘cassava mosaic virus’, which has been advancing across East Africa since the late 1980s, leave visible marks on the foliage but always spare some of the crop.

Brown streak is a stealth virus. It has been known since 1935 when British scientists reported it in coastal Tanganyika but, until recently, it remained largely confined to Tanzania’s low-lying coastal plains. Now it has become much more virulent – apparently starting from this farm in Zanzibar. It is a threat to the whole of sub-Saharan Africa. According to the Institute for Tropical Agriculture’s branch in Dar es Salaam, cassava yield in Tanzania has fallen by between 50 and 80 per cent and during the past five years. The economic damage to farmers is conservatively estimated at more than $50 million a year.

The institute has cross-bred some of the local varieties in Zanzibar with other varieties that seem to tolerate the new virus. The first trials have been successful and some of the new varieties have now been released to farmers in Zanzibar so moving from trials to a fully operational project. Farmers in Zanzibar are clamouring for the new varieties especially a variety called Kiroba which is a favourite because of its sweet taste and smooth texture.
Thank you John Rollinson for sending this news – Editor

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