Cassava

(Manihot esculenta)

Cassava is a perennial woody shrub with an edible root, which grows in tropical and subtropical areas of the world. Cassava originated from tropical America and was first introduced into Africa in the Congo basin by the Portuguese around 1558. Today, it is a dietary staple in much of tropical Africa.

It is rich in carbohydrates, calcium, vitamins B and C, and essential minerals. However, nutrient composition differs according to variety and age of the harvested crop, and soil conditions, climate, and other environmental factors during cultivation.

Importance
In sub-Saharan Africa (SSA) cassava is mainly a subsistence crop grown for food by small-scale farmers who sell the surplus. It grows well in poor soils with limited labor requirements. It provides food security during conflicts when the invader cannot easily destroy or remove the crop, since it conveniently grows underground. Cassava is usually intercropped with vegetables, plantation crops (such as coconut, oil palm, and coffee), yam, sweet potato, melon, maize, rice, groundnut, or other legumes. The application of fertilizer remains limited among small-scale farmers due to the high cost and lack of availability. Roots can be harvested between 6 months and 3 years after planting.

Apart from food, cassava is very versatile and its derivatives and starch are applicable in many types of products such as foods, confectionery, sweeteners, glues, plywood, textiles, paper, biodegradable products, monosodium glutamate, and drugs. Cassava chips and pellets are used in animal feed and alcohol production.

Production
More than 228 million tons of cassava were produced worldwide in 2007, of which Africa accounted for 52%. In 2007, Nigeria produced 46 million tons making it the world's largest producer. According to 2002 FAO estimates, Africa exports only one ton of cassava annually.

Cassava production depends on a supply of quality stem cuttings. The multiplication rate of planting materials is very low compared to grain crops, which are propagated by true seeds. In addition, cassava stem cuttings are bulky and highly perishable as they dry up within a few days.

Harvesting
Nineteen million hectares of cassava were planted worldwide in 2007, with about 63% in Africa. Cassava requires less labor than all other staple crops (21% in working days as compared to maize, yam and rice). However, it requires considerable postharvest labor because the roots are highly perishable and must be processed into a storable form soon after harvest. Roots can be harvested between six months and three years after planting.

Many varieties contain a substance called cyanide that can make the crop toxic if inadequately processed. Various processing methods, such as grating, sun drying, and fermenting, are used to reduce the cyanide content.

Consumption
Nearly every person in Africa eats around 80 kilograms of cassava per year. It is estimated that 37% of dietary energy comes from cassava. The Democratic Republic of Congo is the largest consumer of cassava in SSA, followed by Nigeria.

Disease and constraints
The major pests of cassava in SSA are the cassava green mite and the variegated grasshopper. The main diseases affecting cassava are cassava mosaic disease (CMD), cassava bacterial blight, cassava anthracnose disease, and root rot. CMD alone accounted for an estimated 47% of East and Central Africa's cassava production losses during a serious outbreak beginning in the early 1990's until 2006. Pests, disease and poor cultivation practices combined can cause yield losses as high as 50% in all of Africa.

IITA's research and impact
IITA scientists have played a leading role in developing improved cassava varieties which are disease- and pest-resistant, low in cyanide content, drought-resistant, early maturing, and high yielding. Disease-resistant varieties give sustainable yields of about 50% more than local varieties. Distribution of CMD-resistant varieties in response to the CMD outbreak in East and Central Africa resulted in production levels recovering to pre-epidemic levels in less than five years. Improved cassava varieties are now used in most cassava-growing countries in SSA.

IITA's biological control program resulted in a 95% reduction in cassava mealybug damage and a 50% reduction in damage caused by the cassava green mite.

Post-harvest strategies include the development of effective and simple machines and tools that reduce processing time and labor, and production losses. With these machines, losses can be reduced by 50% and labor by 75%.

During the past three decades, IITA has trained more than 9000 researchers and technicians in ten African countries in processing and in new uses for high quality cassava flour (HQCF). As a result, the private sector in Madagascar, Nigeria, Tanzania, and Uganda have begun using HQCF as a raw material for processing secondary products such as biscuits and noodles.