Cassava Disease

About this time last year, the Economist featured an article about the spread of new varieties of stem rust, a fungal disease which can cause significant crop losses in wheat. The variety of stem rust causing most anxiety among agricultural scientists is rather unimaginatively called UG99, having been first observed by Ugandan researcher William Wagoire in 1999.

Stem rust (pictured) is not a new disease: the late great Norman Borlaug's work initially focused on breeding stem rust-resistant wheat varieties, when he made the serendipitous discovery of the gene Sr31 that not only increased tolerance to stem rust, but also substantially increased yields (and was one of the most important contributors to the Green Revolution in the 1960s).

It's not clear yet how widespread Ug99 will become, or how it can be controlled, and so it presents a considerable threat to the world's most important food crop (alongside rice).

Given the importance of agriculture, it used to surprise me how seldom news stories like this appear. On reflection, though, perhaps it isn't really so surprising. I recently read, for the first time, Amartya Sen's long essay Poverty and Famine, in which the renowned economist argued that famine was caused not by the non-availability of food, but rather by inefficient food distribution mechanisms and a lack of money. Experience bears this out - when was the last time anyone heard of a serious food shortage in a wealthy country with decent roads and other infrastructure? As a result of this - and the separation of modern urban life from the soil - the overwhelming majority have no experience or understanding of agriculture. A constant food supply is taken for granted, so why on earth would agriculture be in any way newsworthy?

This week, however, I was surprised to hear a similar story on BBC World Sevice on another critical staple crop, cassava. As many as a billion people depend on cassava's starchy roots as a staple food, and yet it is hardly known outside the tropics (except in the long-deceased tapioca pudding of my youth). It is particularly important in West Africa, and also in parts of East & Central Africa.

Cassava is an excellent food security crop, as it can survive in drought conditions. In areas of Uganda, it is treated as a "food bank" - when supplies of fresh matooke bananas or other staples run low, cassava roots provide a reserve source of carbohydrates. In other parts of the world, cassava is also used for industrial starch production, for animal feeds and, more recently, as a feeder crop for ethanol production.

TheBBC report highlighted a report just published by the International Centre for Tropical Agriculture. The report warns of the dangers presented by cassava's four most damaging pests and diseases: cassava mosaic disease (pictured), green mite, brown streak disease and whitefly. The report urges the establishment of early warning systems for disease outbreaks, so that they can be contained quickly and effectively before spreading to other regions. Cassava, like bananas and potatoes, is propagated using plant cuttings rather than conventional seed. This means that infected plants can move rapidly from region to region, increasing the risk of disease transmission.

It's not the exciting political news that keeps us glued to CNN and Al-Jazeera newsfeeds. But, for the billions that make up the so-called bottom of the pyramid, it's a lot more important.