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A Website on Improvement

of African Crops and Seed Systems

Biotechnology, Breeding & Seed Systems for African Crops

An Activity of The Rockefeller Foundation’s Food Security Program

Background Information on Cassava

Although still a subject of some debate, the center of origin of cassava is generally believed to be the southern border of the Amazon basin.  Cassava was introduced in Africa in the Congo River delta by the Portuguese in the 15th century, and spread rapidly to many agroecologies. Cassava is today grown in most agro-ecologies of the continent, however, cassava is most important in farming systems of the humid forest regions, where the productivity of grain crops is reduced by low sunlight, foliar pests and diseases, and grain storage is more difficult. Cassava has very high yield potential, making it a viable alternative to grain crops where populations pressures have led to tradeoffs between food quality and quantity.  Commercial cassava yields as high as 20 MT ha-1 have been registered under experimental conditions.  However, because of high labor requirements at planting and harvest, cassava production throughout the world continues to be primarily by small scale, non-mechanized systems.

Cassava is well-known for being able to grow and produce food even in very poor soils.  For that reason, it is often grown at the margins of farms where the better land has been reserved for the production of grain crops.  In addition, once established, cassava is relatively drought tolerant, and when mature can survive up to six months without rains.  Cassava’s ability to produce food under marginal conditions has made it a popular crop of Africa’s poor farmers who are unable to invest in fertilizer or pesticides to protect the crop against environmental stresses and biotic constraints.  This fact, coupled with asexual propagation of the crop, has created a major role for crop improvement – not only are their few other alternatives to building in the performance traits needed by farmers, but, once done, there is a very good chance the crop will stably express those traits.

Cassava is widely consumed as a porridge, which is prepared from dried and pounded roots, but is eaten in a very wide range of forms in different parts of the continent.   Cassava is reported to be consumed in 28 different forms in Cameroon, alone.  In urban areas of west Africa, widespread development of cassava processing methods (consisting of pounding, soaking, and drying to produce a fermented flake known as “gari”) have resulted in cassava becoming an important commercial commodity.  Such processing capacity does not exist in east and southern Africa, and cassava has remained a traditional, rural starchy staple in that region.

Cassava is also consumed as a snack food in various parts of the continent.  Varieties used as snack food are ‘sweet’ types, low in cyanic acid, which can be boiled and eaten or even consumed raw.  Rapidly increasing cassava cultivation is Sahelian countries over the past decade has been primarily based on the use of these types.  Cassava is also widely grown for its leaves, which are used in making sauces.  Once again, leaves from varieties with high cyanic acid content must be properly processed to remove the toxic compounds.  Cassava flour is also sometimes used in making bread for local consumption.  Recently, initiatives in west Africa have aimed at developing the export market potential for production of dried cassava chips used as animal feed in Europe.  This market is currently supplied by Asian production.

Cassava’s combined abilities to produce high yields under poor conditions and store its harvestable portion underground until needed make it a classic “food security crop”.  In recent years, this has proved of critical importance to many people in Africa caught up in civil conflicts and unable to cultivate the normal range of annual crops.  Displaced groups of people in Mozambique during that country’s 16-year war often survived on abandoned cassava fields.  Because it is a vegetatively-propagated crop, such plantings can also serve as a ready supply of planting material during rehabilitation following conflict or drought.  It is a notable fact that cassava processing and marketing are often controlled by women.  Thus, resources from cassava production are often targeted toward the needs of women and children.

As implied above, however, cassava’s productive capacity in low-input conditions comes at a certain cost in terms of carbohydrate quality and protein concentration. 

While aggregate production statistics on cassava are subject to large degrees of error, the figures in Table 24 give a general idea of the trend in cassava production in Africa.  According to figures from the FAO (1999), the rate of increase of cassava production has been higher than any other crop in Africa over the past fifteen years.  Since 1990, this increase has been fueled by rapid increases in productivity following the release of improved varieties in Nigeria, and more recently, in the Sahel. 

The single biggest biological constraint to cassava production in Africa is cassava mosaic disease.  In spite of the availability of many varieties with resistance to this disease, most farmers continue to cultivate susceptible, land race varieties.  Other important targets for breeding programs include resistance to cassava green mites and bacterial blight.  More widespread, participatory evaluation of resistant materials, as well as more decentralized breeding programs, is required.