Yam for sale at a riverside market in Enugu, eastern Nigeria

The time-honoured yam, which is mainly grown in West Africa, is also a product for the future. Improved varieties, which are more productive or better suited to urban consumers, are helping to ensure a boom for the tuber.

There are more than 600 species of yam. Most are tropical, and about a dozen are cultivated on a regular basis. The most common are Dioscorea cayensis (yellow-fleshed) and Dioscorea rotundata (white-fleshed). Used in Papua New Guinea as early as 10,000 years ago, the yam is still widely grown in backyards in the Pacific Islands – especially in Vanuatu – and in the Caribbean, most notably in the Dominican Republic and Haiti. But West Africa accounts for more than 95% of global output. The ‘yam belt’ covers five countries: Benin, Côte d’Ivoire, Ghana, Nigeria and Togo. Of the 4.6 M ha planted worldwide in 2007, 4.3 M were in Central and West Africa. Nigeria easily leads the field with 66% of global output, producing 53 M t in 2008, according to FAO.

An annual herbaceous plant, the yam has long climbing stems which wind themselves around supports. A single plant produces between one and five tubers of varying shapes, each weighing up to 5 kg. Certain species produce dioscorine, a toxic alkaloid that is destroyed by cooking. Rich in starch and protein, yam is very popular. It grows in light, well drained soils and often the most fertile land is set aside for it.

Over the years, producers have faced a number of difficulties, partly due to growing demand and more intensive production. Declining soil fertility, an increase in disease linked to crop intensification and the high cost of seed – which accounts for 30 to 50% of production outlay – have created major obstacles to its development. As a result, yam has been the focus of a number of research projects. Several have produced convincing results.

Research to the rescue

For years, production systems for cultivating yam remained traditional, including the varieties grown and the crop management applied. Then, in the 2000s, research programmes developed new high-yielding improved varieties, which were resistant to parasites and had good culinary qualities. The results were extremely positive, with improved varieties often passing from one farmer to another more quickly than via extension agents. Evidence of renewed global backing for the yam as a source of revenue and food security has come in the form of EU support, since early 2010, for the Strengthening Capacity for Yam Research-for-Development in Central and Western Africa research programme. Managed by the International Institute of Tropical Agriculture (IITA) in Nigeria, the programme brings together 13 research institutes from six countries: Benin, Cameroon, Côte d’Ivoire, Ghana, Nigeria and Togo. It seeks to offer a sub-regional research response to the challenges facing producers.

New products for urban consumers

At least 60 million people in Africa eat yam as part of their daily diet, with an average consumption of 61 kg/capita in West Africa. In this region, the favourite dish is fufu (pounded yam), but the tuber is also eaten braised, boiled or fried. Flour is made from yam chips, which have been parboiled and dried. It is used to make couscous, dumplings and paps. Since fresh yam is only available on a seasonal basis, the introduction of yam flour has contributed to the crop’s development and to accessing urban markets.

Urban yam consumption now accounts for 48% of total output. But there is still plenty of scope to exploit town markets further. For processing, studies on West Africa’s yam sector recommend developing simple techniques such as mechanical slicing to facilitate drying. This would reduce some of the marketing constraints for fresh tubers and would promote diversification for a product that is highly prized by African consumers.

3,000 varieties to preserve

In most African countries where yam is currently grown, many potentially important varieties only exist in fields, and there is a risk that they will disappear, destroyed by conflicts or natural disasters.

To tackle this challenge, producers and scientists have launched an ambitious initiative to preserve yam biodiversity. The goal is to protect 3,000 tissue samples in gene banks. The project, headed by IITA in partnership with the Global Crop Diversity Trust, will focus on African varieties but will also include yam from the Caribbean and Pacific. Preserving past centuries of yam cultivation is also a way of assuring the crop’s future.



 
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