Cassava roots © Gustavo, Adobe Stock

Roots and tubers

Tropical starchy root crops and tubers – cassava, sweet potato, yam and dasheen –, or "RTs", play a vital role in food security for populations in tropical zones, against a backdrop of population growth and rapid urbanization, particularly in Africa. CIRAD has substantial expertise in these value chains, ranging from genomics to postharvest technology through varietal improvement, plant health, cropping systems and value chain economics. CIRAD's approach is multidisciplinary and often innovative.

The figures

Roots and tubers: a vital food resource, particularly in Africa

Total RT production comes to more than 830 Mt (37% in Africa) and 460 Mt (60 % in Africa) excluding potatoes (FAOSTAT, 2018). Cassava is the leading crop, with 278 million tonnes worldwide (61% in Africa), followed by sweet potato (92 Mt, 28% in Africa), yam (72 Mt, 97% in Africa) and dasheen and macabo (11 Mt, 80% in Africa).
Per capita RT consumption worldwide is around 70 kg/year, compared to 147 kg for cereals.
In Africa, the figures are around 150 kg/person/year for both groups of products (albeit with different dry matter contents: 90% for cereals, 30-40% for RTs). Consumption levels are much higher in some African countries. In Congo, the figure is 250 kg of cassava/person/year, in Ghana 220 kg. In Nigeria, almost 120 kg of cassava and 105 of yam, in Benin 110 and 155 kg respectively. Outside Africa, only Paraguay consumes large volumes of tropical RTs, with more than 120 kg of cassava/person/year.

Africa is thus the focal point for the strategic issues surrounding these value chains. Consumers have very high expectations in terms of quality, since these products are used for very specific local culinary preparations to which they are very strongly attached.

The issues

Productivity still falls well short of potential

Tropical RTs have benefited from significantly less investment in their improvement than cereals or even potato, of which 2/3 of production is concentrated in temperate zones. Average yields are relatively low (10 t/ha) in relation to potential, which tops 100 t/ha in some cases. There is therefore substantial room for improvement, whereas cereal yields have now peaked in the world's most intensive farming systems.

Processing and storage: means of improving quality

Because they are perishable in their unprocessed form due to their low dry matter content (20 to 40%), RTs are often processed (drying, fermentation) to stabilize the product and make it easier for consumers to use. The techniques used are often manual, but are become increasingly industrial, in response to demand from rapidly growing urban markets and to changing consumption methods, and in order to develop products with innovative functional and nutritional properties, for which there is strong demand from the agrifood industry.

Innovations for the fast-growing cassava starch value chain

Only cassava is processed industrially on a large scale, in Asia and Africa, to make starch for food and non-food use (biopolymers, ethanol). These fast-growing agro-industrial chains call for new production and processing systems.

Roots and tubers are more resilient to climate change

Most foresight studies consider RTs to be more resilient to climate change than grain crops (cereals and legumes) and should see their production zones expand, particularly in Africa. However, this largely under-used potential could be under threat from the emergence and spread of new diseases (such as the cassava viruses CMV and BSV). The vegetative propagation techniques used in fact foster the spread of such diseases, for want of efficient, safe seed systems .

In view of the current situation, RT-based supply chains are likely to expand and play a greater role in food security and the see their role in food security and the agricultural economy in future. This is particularly true in Africa, where the expected doubling of the population in the coming decades, rapid urbanization and changes in food habits mean greater demand for processed convenience foods.

Research requirements to support the development of these value chains are high and continuing to grow. CIRAD has a wide range of skills and expertise in this field.