Unlocking the diversity of yam

IITA scientists inspect yam plants in the field gene bank. Photo by O. Adebayo, IITA.
IITA scientists inspect yam plants in the field gene bank. Photo by O. Adebayo, IITA.

The International Year of Biodiversity (IYB) has emphasized the need for global action that will unravel the genetic diversity of yam, a root crop that provides food security to 300 million people in sub-Saharan Africa.

Yam is grown in about 51 countries in the tropics and subtropics, with yields averaging about 11 t/ha in the major producing countries of West Africa (Nigeria, Cote d’Ivoire, Ghana, and Bénin). However, little is known about the tuber crop’s diversity.

“This aspect is important for yam improvement to meet the demand of people depending on this crop for food and livelihood,” says Ranjana Bhattacharjee, IITA Scientist working on fingerprinting the yam germplasm collection.

Yam provides calories and puts money in the pockets of farmers. The tuber-bearing climbing plant from the genus Dioscorea also plays a major role in sociocultural activities in West Africa including traditional marriages and the New Yam Festival.

Globally, there are over 600 species of yam but only a few are cultivated for food or medicine. Scientists fear that some species are threatened and might become extinct as a result of climate change and genetic erosion. This prompts the calls for conservation.

The major edible species of African origin are white Guinea yam (D. rotundata Poir.), yellow Guinea yam (D. cayenensis Lam.), and trifoliate or bitter yam (D. dumetorum Kunth). Edible species from Asia include water or greater yam (D. alata L.), and lesser yam (D. esculenta [Lour.] Burkill). Cush-cush yam (D. trifida L.) originated from the Americas. White Guinea yam and water yam are the most important in terms of cultivation and use.

Yam tuber. Photo by IITA.
Yam tubers. Photo by IITA.

This preferred staple is usually eaten with sauce directly after boiling, roasting, or frying. The tubers may also be mashed or pounded into dough after boiling, or cooked with sauces and oils. They can be processed into yam balls, chips, and flakes.

Fresh yam tubers are peeled, chipped, dried, and milled into flour that is used in preparing dough called amala (Nigeria) or telibowo (Bénin). Commercial products based on dry flakes or flours from the tuber are produced in Nigeria, Ghana, and Côte d‘Ivoire for export and sale in urban areas.

Though millions depend on the crop, especially in sub-Saharan Africa, not many outside of Africa know about the tuber’s potential for commercialization, and its role in enhancing food security in the region, according to Robert Asiedu, Director of the Program on Root and Tuber Systems at IITA.

“We talk about yam tubers as a food staple of millions of Africans to donors or investors who don’t even know what yam is, how it looks or tastes. So the question is: How would they even think of investing in research in a ‘little-known’ staple like yam?”

Perhaps yam’s low profile in the developed countries or in the West is the major limitation in attracting funding for research, but this hardy tuber is an important “part of man” especially in Africa, the Caribbean, Asia, and the South Pacific Islands where it is widely eaten. According to Asiedu, it is the “preferred and most appreciated staple food and calorie source” in areas where it is grown.

Yam faces constraints that include the high costs of planting material and of labor, decreasing soil fertility, the inadequate yield potential of varieties, and increasing levels of field and storage pests and diseases associated with intensive cultivation.

To tackle some of these constraints, work at IITA for the last few years has focused on improving the tuber, primarily white and yellow Guinea yam, and water yam.

Man with huge yam tuber. Photo by IITA.
Man with huge yam tuber. Photo by IITA.

The breeding program uses the 2,216 accessions of Guinea yam and 816 of water yam in IITA’s genebank to study resistance to anthracnose and virus diseases. Improved populations have been developed with partners in the national agricultural research and extension systems (NARES), who have released varieties in Nigeria (National Root Crops Research Institute, 7) and Ghana (Crops Research Institute, 3).

Despite the success in yam improvement, new challenges keep on coming, prompting researchers to use other tools, such as molecular characterization to unlock the genetic diversity of yam.

Recently, the Global Crop Diversity Trust funded a project in IITA to duplicate, document, and distribute the germplasm of yam to other partners in accordance with the International Treaty on Plant Genetic Resources for Food and Agriculture. Such support is indeed a milestone in yam research. The project also aims to fingerprint the entire germplasm collection at IITA. This will help in understanding the extent of genetic diversity present in the collection. From this, the genes for important traits can be determined through association mapping, a tool that could be used successfully to improve and sustain the crop.

As the world marks the IYB, serious attention from other donors is necessary to keep the crop as a “part of man.”

3 thoughts on “Unlocking the diversity of yam

  1. Thanks for a great report on yams. I ate some for the first time when I visited Jamaica a few years ago.

    David

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