Cassava: the food of the poor for future food security

Grown in over 90 countries, cassava provides 500 million people with food and a livelihood. Better known as mandioca, manioc, yucca, and tapioca, cassava is one of the main crops supporting
food security worldwide.

However, the pity is that cassava is also a major ‘orphan'(1) crop.

Highly rich in carbohydrates, being the third source of calories in the tropics after rice and corn (Source: FAO, 2002), cassava does not appear in the statistics for industrial agriculture,
but rather has been confined to marginal lands in the poorest countries practicing subsistence agriculture.

Its adaptability to different environments as well as tolerance to long periods of drought make it one of the most frequently grown crops in numerous agroecosystems of tropical and sub-tropical
regions.

Cassava and similar crops could represent the future of food security in the poorest regions and contribute to achieving the first of the eight Millennium Development Goals(2) that aims to
halve worldwide hunger and poverty by the year 2015.

Let’s try and understand how through a short journey to discover this interesting crop.

The origin and importance of cassava
Cassava (Manihot esculenta Crantz) is a perennial shrub of the family Euphorbiaceae.

Originating from the Amazon basin, where it has been cultivated for more than 5000 years, cassava is mainly consumed as a food crop for its starchy roots.

Throughout the centuries cassava has spread widely to many areas of Asia, Africa, and Latin America.

Introduced to Africa by the Portuguese during the 16th century, cassava colonized various agroecological environments and is now the major food crop in most African countries.

Cassava is grown at the margins of small farms managed by women – often in association with other crops – and is mainly used for local consumption.

Alfred Dixon of the International Institute of Tropical Agriculture (IITA) in Nigeria says ‘Cassava is to the African peasant farmers what rice is to the Asian farmers, or what wheat and potato
are to the European farmers.’

Cassava is potentially a very high yielding crop. Its starchy roots produce more calories per unit area than any other crop except sugarcane.

Moreover, in contrast to other crops such as maize, cowpea, yam, and millet, which are ecoregionally specific, cassava is probably the only crop grown across the whole of Africa.

This is due to its ability to tolerate highly unfavourable environmental conditions.

Once mature, roots can survive in the ground for a long period of time without water, maintaining their nutritional value intact.

Compared to cereals this gives cassava a unique advantage, and makes it an excellent base supply for food security, particularly in critical times of drought, famine, and the political and
socio-economic upheavals that frequently affect cassava consuming countries.

From tubers to flour
Cassava is used as a basic food staple for human consumption, starch source, and also for animal feed.

It is mainly consumed as boiled flour obtained by processing the root.

The roots are very rich in carbohydrates, mainly starch (about 80% dry weigh).

They also contain vitamin C, beta-carotene, calcium, potassium, and food fibers, but are very low in protein (0.5-1.5% fresh weigh) and fat (about 0.17%).

The leaves are consumed less than tubers and have a large amount of protein (about 7% fresh weight).

In evaluating the nutritional value of cassava, its great concentration of cyanogenic glucosides is not to be undervalued.

Cyanogenic glucosides belong to a group of secondary metabolites contained in the cell vacuoles, which are potentially toxic.

Fresh cassava roots contain two types of glucosides: linamarin (93%) and lotaustralin (7%).

After cell damage they are hydrolyzed by endogenous enzymes – such as linamarase – which are normally present in the cell wall separated from glucosides, thus releasing cyanidric acid.

If present in certain quantities, cyanogenic glucosides can cause acute cyanide poisoning and chronic toxicity, often associated with malnutrition.

This is the case with Konzo, a nervous pathology mainly affecting women and children, leading to progressive paralysis.

The quantity of cyanogens depends on cassava cultivars and growing conditions.

In particular, the two types of cassava recognized are the ‘sweet’ variety with a small amount of glucosides, and the ‘bitter’ cassava with a larger amount.

Thanks to suitable methods of storage and processing for tubers, it is now possible to reduce the plant toxicity notably, also preventing its fast post-harvesting deterioration.

One of the most effective techniques of lowering the cyanogen content to a safe level involves grinding the roots into granules.

The resulting granules are then macerated under water at room temperature.

This process helps fermentation and conversion of glucosides into gaseous cyanidric acid.

Once released into the environment it volatilizes rapidly at tropical temperatures.

The final product is toasted to produce a dried granulated flour.

If properly processed, cassava roots form an important food supply.

Furthermore, provided that root consumption is associated with a source of protein or greater use of leaves, cassava could be the right ingredient in a balanced diet to solve malnutrition
problems in all cassava consuming countries.

Cassava and biotechnology: a scientific challenge achievable through co-operation
Despite its marginal role within agricultural research, cassava has unique characteristics that are crucial to dealing with subsistence and food security issues in consuming countries.

Being very common in Africa, cassava could potentially replace wheat flour in various products such as bread.

Moreover, starch extracted from the roots is used as row material for the food industry and in other fields, and could open new frontiers to crop marketing on a large-scale, both for domestic
trade and exportation, as has already happened in some Asian countries.

These are the aims of research institutes and centres that have used their human and financial resources for the development and improvement of cassava.

One of the leaders in innovation that has made a large contribution to the crop’s success in many parts of Asia and Latin America is the CIAT (International Center for Tropical Agriculture),
which has been active in cassava research since the 1970s.

Based in Colombia, CIAT has a global mandate for cassava research within the CGIAR (Consultative Group on International Agricultural Research).

Fundamental responsibilities inherent in the CIAT’s mandate are safeguarding, studying, and sharing germplasm, which researchers must evaluate and improve, therefore making genetic resources
available to colleagues worldwide.

For this reason, the Center maintains a collection of more than 6000 cassava accessions for the FAO (Food and Agriculture Organization of the United Nations), including landraces from Asia and
Latin America, clones selected by the CIAT and the IITA, and several wild Manihot species.

Apart from being involved in various ongoing global initiatives relating to yield and nutritional improvement of orphan crops, the CIAT is also the driving force of the CBN (Cassava
Biotechnology Network).

Established in 1998, the CBN links advanced research institutes to national and regional programmes, bringing together local farmers and researchers from all over the world to address the main
biotechnological challenges in cassava research, therefore reinforcing its value for food security and economic development.

Firstly, to sustain its food security role, cassava production must be increased and stabilized by developing genetic resistance to major pathogens and diseases as well as tolerance to abiotic
stresses.

Another important goal is to identify and exploit genetic mechanisms for slowing the post-harvest deterioration of cassava tubers.

Thirdly, improved traits must be introduced in a wide variety of genotypes satisfying the various tastes and preferences in consuming countries.

This can be achieved easily thanks to vegetative propagation of cassava, which allows farmers and researchers to fix any gene combination into clones.

Now a brief overview of the main cassava biotechnological innovations is presented.

Researchers at Ohio State University are developing cyanogen-free transgenic cassava, which is also resistant to most pathogens.

A research group at the University of Bath is studying cassava varieties which are more resistant to post-harvest deterioration.

A researcher at EMBRAPA (Empresa Brasileira de Pesquisa Agropecuaria, Brazilian Agricultural Research Corporation) discovered cassava varieties kept through centuries by indigenous tribes in
the Brazilian Amazon.

Among these, there is a yellow variety rich in beta-carotene and another variety that produces sugar instead of starch.

Furthermore, CBN members have developed a molecular genetic map of cassava, the first such map ever to be generated for a major crop outside the realms of industrial agriculture.

The CBN is an example of a vehicle through which technological innovation in cassava is passed from research centers directly to local farmers.

In this sense the CBN is highly revolutionary in terms of the structure and organization of international agricultural research and demonstrates how biotechnology and cooperation can work
together to reinforce world food security.

Alessandra Vessia

Notes
(1) The term orphan is meant to address the so-called ‘minor’ crops that receive little or no attention from the scientific world nor funding for research and development
projects in agriculture in spite of their unquestionable importance for food security in the world’s poorest countries (Source: Naylor et al, 2004. See citation). Besides cassava, other orphan
crops are millet (Panicum miliaceum), taro (Colocasia esculenta), sweet potato or yam cultivars (Ipomoea batatas), and cowpea (Vigna sinensis).

(2) Through the 1990s a group of fundamental goals were identified at various international summits and conferences held to discuss development throughout the world. These goals were put
together in the Declaration adopted in 2000 by the UN Millennium Summit, and later defined the eight Millennium Development Goals (Source: FAO, Food and Agriculture Organization of the United
Nations).

Bibliography
Aerni P. (2006). Mobilizing science and technology for development: the case of the Cassava Biotechnology Network (CBN), AgBioForum , 9(1): 1-14.

FAO (2002). Partnership formed to improve cassava, staple food of 600 million people. https://www.fao.org/english/newsroom/news/2002/10541-en.html

Naylor R.L., Falcon W.P., Goodman R.M., Jahn M.M., Sengooba T., Tefera H., Nelson R.J. (2004). Biotechnology in the developing world: a case for increased investment in orphan crops, Food
Policy,29: 15-44.

Siritunga D., Sayre R.T. (2003). Generation of cyanogen-free transgenic cassava, Planta, 217(3): 367-373.

Teles F.F. (2002). Chronic poisoning by hydrogen cyanide in cassava and its prevention in Africa and Latin America, Food and Nutrition Bullettin, 23(4): 407-412.

Links
CBN – Cassava Biotechnology Network
http://www.ciat.cgiar.org/biotechnology/cbn/

CGIAR – Consultative Group on International Agricultural Research
http://www.cgiar.org

CIAT – International Center for Tropical Agriculture
http://www.ciat.cgiar.org

EMBRAPA – Empresa Brasileira de Pesquisa Agropecuaria
http://www.embrapa.br

IITA – International Institute of Tropical Agriculture
http://www.iita.org

FAO and The Millennium Development Goals
http://www.fao.org/mdg/goals.asp

University of Bath – Cassava Genetic Research Site
http://www.bath.ac.uk/bio-sci/cassava-project