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.”

A tough puzzle: Biodiversity and NRM

Peter Neuenschwander, p.neuenschwander@cgiar.org


In the past, natural resources management covered approximately half of all activities and funds of IITA and similar institutes in the Consultative Group on International Agricultural Research (CGIAR). Most often, it did not include the conservation of wild biodiversity. The other half of funds and personnel were allotted to crop plant biodiversity, mainly the varieties available worldwide in genebanks. Increasingly, however, farmers’ varieties and wild relatives of crop plants became important and the biodiversity of pathogens and witchweed were investigated in view of their use for resistance breeding.

Thanks to new technologies, breeding barriers between species could be overcome and foreign genetic material was incorporated into so-called “genetically modified organisms” (GMOs). These are being tested at a relatively small scale in some African countries. They are the source of real worries and polemical distortions, while countries such as the USA, China, Argentina, Brazil, and India have chosen to grow some GMOs on vast areas. Today, GMOs are at the center of a heated debate in an unnecessarily antagonistic manner, pitting the ideals of biodiversity conservation against the need to feed the world.

Since the end of the 1980s, the importance of biodiversity in general for a sustainable future of Planet Earth has been increasingly publicized. At the Rio Conference in 1990, global warming and the loss of biodiversity were singled out as the two most important issues facing mankind. The climate conference in Copenhagen last year was supposed to reach goals on halting and mitigating climate change. The conference is generally considered to have been a failure; nevertheless, great efforts to avoid a climatic disaster are being taken by many governments, even without the wished-for strict regulations.

And here we are in 2010, the “International Year of Biodiversity”. International nongovernmental organizations such as the International Union for Conservation of Nature (IUCN), BirdLife International, and many others are highly active in conservation and their efforts are showing successes. Most countries have subscribed to their ethics, signed the international treaties, and established focal points for the Convention of Biodiversity. For the CGIAR, though, biodiversity conservation mostly remains germplasm conservation. It is the world leader in the conservation of genetic material of crop plants and their wild relatives (for instance, yam and cowpea, of particular interest in West Africa). It is instrumental in the development of rules and regulations about the ownership of germplasm under the umbrella of the Food and Agriculture Organization.

Meristem excision under aseptic conditions (laminar flow workstation) using stereomicroscope, IITA genebank. Photo by IITA.
Meristem excision under aseptic conditions (laminar flow workstation) using stereomicroscope, IITA genebank. Photo by IITA.

IITA is also co-developing best practices and tool kits for collecting germplasm and houses important pathogen collections. Generally though, conservation of other forms of biodiversity is treated rather timidly. The general antagonism between agriculture and nature conservation thus persists. Yet, it probably need not be so: In 2001, IUCN and Future Harvest came together to publish a policy paper outlining ‘The common ground and common future, how eco-agriculture can help feed the world and save wild biodiversity’. While some of the claims might be overwrought, enough is known to allow progress towards the twin goals of saving the bulk of biodiversity while feeding the human population.

Insects are the majority of all described species. On a worldwide level, BioNET INTERNATIONAL organizes and stimulates the coordination of taxonomic research (of all taxa, but with special emphasis on insects). The IITA biodiversity collection of insects, housed in IITA-Bénin, serves as the network center for West and Central Africa. This collection, the largest in the CGIAR, is instrumental in providing basic information about the biodiversity of natural enemies used in all types of biological control.

In addition, the insectary at IITA-Bénin houses numerous live beneficial insects and mites. IITA-Bénin can respond to the changing situations of ever more invading insects and mites. Thus, in the last few years and in West Africa alone, we have seen the invasion and sometimes the control of spiraling whitefly, a new invading fruit fly (Sri Lanka fruit fly), and very recently the papaya mealybug. Last year, when the cassava mealybug invaded Thailand, IITA was able to provide effective parasitoids without delay.

Many more natural enemies are out there in the wild, suppressing their hosts or their prey. Most concern agricultural pests, but increasingly, conservation biological control is becoming important to save natural habitats from invaders. IITA is participating in these international efforts through its biological control of floating water weeds across Africa.

To assess the elusive so-called “ecosystem services”, sophisticated biodiversity studies are required. IITA’s historic classical biological control projects were against cassava and mango mealybug and cassava green mite, three formidable agricultural pests. The first two were not even known to science before they appeared in new habitats. These examples from South America and India illustrate how the ‘ecosystem services’ provided by pests’ natural enemies in the home environments remain hidden until harmful insects and mites get dissociated from their predators. Important services are also provided by microbials and pollinators, but these become visible to farmers and policymakers only when their function is impaired. Examples are lack of conservation because of wanton destruction or by bad agricultural practices, such as those that lead to the depletion of nutrients in soils or the destruction of suppressive soils.

Researcher monitoring cowpea seeds kept in cold storage room in the IITA genebank. Photo by J. Oliver, IITA.
Researcher monitoring cowpea seeds kept in cold storage room in the IITA genebank. Photo by J. Oliver, IITA.

The contribution to sustainable agriculture and conservation that IITA can make is by improving the tools (GIS, sociological, etc.) and by significant advances in research and its application to real world needs. We can thus establish an intellectual agenda for discussion and change within IITA, collaborating organizations, and society at large. Comparing this claim for action with the actual situation at IITA, we find that traditional biodiversity conservation in the form of crop plant germplasm is rather well implemented; but the conservation of nonplant biodiversity is weakly institutionalized and would need better support. Natural resources management offers the intellectual platform to integrate the different disciplines in a sustainable manner. Unfortunately, the inclusion of all biodiversity activities in a holistic natural resources management remains a dream.

Within the period of 20 years, biodiversity conservation has moved from being a specialized field to becoming an urgent task to be carried out before it is too late and extinction takes away the organisms we might one day have to rely on for survival. Even where we do not completely understand the benefits of biodiversity in providing stability to ecosystems, conservation should be implemented for the good of future generations. Apart from research, this also takes the form of providing refuges for biodiversity for future studies, as is the case with the IITA-Ibadan forest or the rehabilitated forest at Drabo Gbo in Bénin. Our national partners have many more examples; they might cherish our leadership in this matter.