Participatory strategies of conserving yam biodiversity in Bénin

A. Dansi (, C. Lusty (, R. Asiedu (, R. Hall, and R. Vodouhè (

Yam (Dioscorea spp.) is an important tuber crop in Bénin. Its production is intensive in Collines (Center), Donga and Borgou (North), but marginal in Atakora (Northwest), Plateau (Southeast), and in Alibori (far north). Four species are cultivated (D. alata, D. cayenensis-rotundata complex, D. dumetorum, and D. bulbifera). Among these, the native African D. cayenensis-rotundata complex remains the most important, preferred, and widely cultivated.

Yam tuber seeds of different accessions ready for transport to IITA genebank for ex situ conservation. Photo from Alexandre Dansi, IRDCAM.
Yam tuber seeds of different accessions ready for transport to IITA genebank for ex situ conservation. Photo from Alexandre Dansi, IRDCAM.

Yam production in Bénin is seriously hampered by numerous constraints including pest and disease pressure, poor soil, and changing climate. Strategic use of existing genetic diversity is thus an appropriate option for addressing these constraints in an affordable and sustainable way. For this diversity to be well studied, conserved, and used, the International Foundation for Science (IFS), Gatsby Charitable Foundation (UK), IITA, Bioversity International, and more recently the Global Crop Diversity Trust (GCDT) sponsored several research projects in Bénin between 1997 and 2009. Within the framework of these projects, different yam germplasm collection surveys have been conducted that led to a unique collection of 1,017 accessions conserved in the field by Crop, Aromatic and Medicinal Plant Biodiversity Research and Development Institute (IRDCAM) in northern Bénin.

The landraces collected were fully documented (origin, agronomic traits, and technological characteristics) and a database was constructed. With the help of farmers, the collected landraces have been fully characterized based on plant morphology and classified into 210 morphotypes. The equivalence of the diverse vernacular names that cause confusion among users has been clearly established. The geographical distribution of the morphotypes, together with genetic diversity analysis, led to the identification of four different zones of diversity. These are Zone 1: Atakora (far Northwest); Zone 2: Bariba cultural area (Northeast); Zone 3: Donga (Northwest); and Zone 4: South-Center.

Yam germplasm collection points. Courtesy of GIS Lab, IITA.
Yam germplasm collection points. Courtesy of GIS Lab, IITA.

Analysis at the community level within each of these four zones revealed the high yam diversity in Bénin in Zone 2 (20–82 varieties per village; 40 on average) and in Zone 3 (13–48 varieties per village; 24 on average). Zone 1 (8–27 varieties per village; 17 on average) and Zone 4 (6–51 varieties per village; 20 on average) had less diversity. Early maturing (double-harvested) varieties dominate Zones 1 and 4, while Zone 3 is dominated by late-maturing (single-harvested) varieties. Both late- and early maturing landraces appeared in almost equal proportions across villages in Zone 2.

Within each of the four diversity zones and at community level, several varieties are disappearing or being abandoned. High rates of genetic erosion (32–48% on average) were recorded almost everywhere. This highlights the necessity and urgency of developing strategies to conserve the existing diversity both in situ and ex situ for use by present and future generations. With the financial support of GCDT, Bénin yam germplasm is already fully regenerated and safely duplicated in IITA’s Genetic Resources Center at Ibadan (Nigeria) where it will be conserved both in vitro and in a field bank.

The causes of the ongoing genetic erosion are diverse (technological, biotic, abiotic, and cultural) and vary in relative importance according to production zones. In the far Northwest (Zone 1), for example, environmental factors, particularly poor adaptation to climate change and susceptibility to poor soils, are the most important. In the Northeast (Zone 2) susceptibility to pests and diseases and cultural beliefs are the principal reasons.

To compensate for the loss in diversity and cope with the environmental (biotic and abiotic) constraints, farmers use different strategies to exploit the existing diversity. In the dry zone of Atakora where climate change is more perceptible, farmers adopt new varieties to adapt production to actual local conditions that are characterized by increasing frequency of drought. They also alter the timing of planting and other agronomic practices. In central Bénin, farmers increasingly neglect D. cayenensis rotundata varieties in favor of those of D. alata since these are better adapted to current agroecological conditions (poor soil, pest and disease pressure, low rainfall, etc.).

To assist farmers with this option for using the genetic diversity, a program for intensive variety exchanges between villages and producers in different diversity zones was launched in 2009 within the framework of the GCDT project. Of 20 to 30 participating villages in each zone, 15 villages have already received new varieties (40 to 50 per village). This year, 15 other villages will also benefit from this program.

Alexandre Dansi (right) and some farmers from Tchakalakou (North Bénin) in a discussion during the participatory yam characterization and classification exercise. Photo from Alexandre Dansi, IRDCAM.
Alexandre Dansi (right) and some farmers from Tchakalakou (North Bénin) in a discussion during the participatory yam characterization and classification exercise. Photo from Alexandre Dansi, IRDCAM.

The exchanges have been conducted, taking into account the preference criteria determined for each zone. This exchange of varieties is a strategic way of conserving diversity on-farm through utilization. It has a multidimensional importance that includes strengthening yam production, food security, poverty alleviation; improvement of household income generation; strengthening diversity, conservation, and use; and improvement of sociocultural conditions of rural women. The results will rapidly become more evident in Zone 1.

In the northern part of this zone negatively affected by climate change, only one to two varieties out of eight to ten are tolerant of drought. The weather is suitable for the production of dry yam chips, which are in high demand and more expensive than fresh yam, but the late-maturing varieties used for this purpose were almost absent. In the south of the zone (Toucountouna and Natitingou region) dominated by lowlands, flooding is a challenge and only a few varieties were reported to be tolerant of high soil moisture.

We believe that by using, through exchanges, a large number of the Bénin yam varieties available, farmers in these regions will have a chance to find at least 50 that will be suitable for their local conditions. A strong network of yam producers in Bénin is actually being organized by IRDCAM to sustain the effort. The farmers highly appreciate the effort.

Cultivated yam are all domesticated from wild relatives co-evolving with the cultivated forms via gene flows. Because these species are sources of useful genes, participatory strategies have also been developed to preserve their diversity in situ while encouraging the domestication process developed by farmers.

Why manage noncrop biodiversity

Muris Korkaric, and Fen Beed,

When it comes to the diversity of nonplant taxa, the numbers alone are highly impressive. There are an estimated 5–30 million species of microorganisms globally but only two million have been formally described. In 1 g of soil, over a billion bacteria cells can be found, but fewer than 5% of the species have been named or can be grown on artificial media. For fungi, about 1.5 million species are estimated to exist and yet only 5% have been characterized taxonomically.

Disease symptom caused by Colletotrichum fuscum on lettuce leaf. Photo by F. Beed, IITA.
Disease symptom caused by Colletotrichum fuscum on lettuce leaf. Photo by F. Beed, IITA.

Nematodes remain particularly poorly described with only a fraction of the suspected half million found in nature known to man. For insects, arachnids, and myriapods only 1.1 million have been named from a potential 9 million. These numbers compare with an estimated 420,000 seed plants of which most have been described.

Knowledge of biodiversity is uneven, with strong biases towards the species level, large animals, temperate systems, and the components of biodiversity used by people. Although biodiversity underlies all ecosystem processes, modern agriculture is based on a very limited genetic pool of crops and an even more limited exploitation of the genetic resources of nonplant taxa.

This is surprising, considering that as a consequence of their diversity microorganisms and insects play pivotal roles across ecosystems that far exceed those of plants. They provide critical functions and services for food and agriculture. They are indivisibly connected with ecosystem resilience, crop health, soil fertility, and the productivity and quality of food. Modern agriculture in the developed and especially the developing world uses only a small fraction from this rich pool of genetic resources.

Conserving and using nonplant taxa
One of the vital pillars in the work of the Consultative Group on International Agricultural Research (CGIAR) is the conservation and use of agrobiodiversity and related knowledge. Over 650,000 accessions of crop, forage, and agroforestry genetic resources are stored and maintained through the centers’ genebank system and distributed to researchers and breeders throughout the world.

However, scientists from different CGIAR centers are also involved in collection, conservation, and sustainable use of insects and mites, fungi, bacteria, viruses, and nematodes that are either beneficial or antagonistic to crops. These research collections are used in two main areas: (1) crop health and productivity, where the collection supports screening for resistance in breeding programs, pathogen diagnostics, and the development of biological control technologies, and (2) soil health, fertility and ecosystem resilience where for example, collections support the development of biofertilizers.

IITA’s main collections of nonplant taxa are housed at the stations in Ibadan (Nigeria) and Cotonou (Bénin). At the headquarters in Ibadan, the collection and study of plant pathogenic fungi, bacteria, and viruses of important crops are coordinated and collections are maintained. Examples are those for yam and cassava anthracnose, cassava bacterial blight, and soybean rust pathogens.

Aflatoxin-producing fungus Aspergillus flavus growing out of maize grains in a culture medium. Photo by J. Atehnkeng.
Aflatoxin-producing fungus Aspergillus flavus growing out of maize grains in a culture medium. Photo by J. Atehnkeng.

Some of the collections contain large numbers of isolates of the same species which are often unique, not being found elsewhere in the world. International repositories might hold many different species, but tend to store fewer isolates per species and rarely prospect across the developing world. A diverse range of isolates gives a more complete representation of the genetic diversity which can be crucial for understanding evolutionary patterns, pathogen variation, and population dynamics. It helps breeding programs to identify targets for resistance selection.

Collections of isolates of the same species can be used to develop appropriate biocontrol technologies. One such example is IITA’s collection of Aspergillus flavus, a fungus that normally produces aflatoxin, a compound that is toxic to humans and animals. Over 4,500 strains have been collected from Nigeria alone and screened for toxin production and their ability to outcompete other strains when found simultaneously on foodstuffs. The atoxigenic and most competitive strains have been used to formulate aflasafe®, a biocontrol product (see R4D Review September 2009 issue).

Also in Ibadan, collections of beneficial soil microorganisms are studied and maintained. These organisms (such as Rhizobia spp. and mycorrhizae) enhance the nutrient uptake of leguminous crops and can be used as biofertilizers.

At IITA-Bénin, microorganisms and arthropods have been characterized and preserved for use in biological control programs to manage invasive crop pests and weeds. Plant pathogens have been identified and stored since the deployment of appropriate control measures first requires definitive identification of the causal agent of the disease. The biodiversity center maintains over 360,000 insect and mite specimens and is one of the largest reference collections in West Africa (see R4D Review September 2009).

Other IITA stations keep smaller working collections of nonplant taxa. At IITA-Uganda, collections of nematodes, bacteria, and fungi are maintained—mainly those associated with banana production. Certain Fusarium strains, for example, are used for endophyte-improved banana tissue culture for enhanced pest and disease resistance.

Looking like strung beads, these are part of a sample of insects received by the IITA biodiversity center in 12 months. Photo by G. Goergen, IITA.
Looking like strung beads, these are part of a sample of insects received by the IITA biodiversity center in 12 months. Photo by G. Goergen, IITA.

IITA is a lead organization for the conservation and use of nonplant taxa across sub-Saharan Africa. It is now characterizing nonplant taxa collections across the CGIAR as part of the World Bank-funded GPG2 project (Phase II of the Collective Action for the Rehabilitation of Global Public Goods in the CGIAR Genetic Resources System). This is the first system-wide inventory and collation of the existing global, nonplant taxa collections. The aim is to provide a coordinated and harmonized service for research and use of noncrop taxa to support durable farming systems in the developing world.

Future challenges and opportunities
There is a growing appreciation of the fact that farming occurs in an ecological context with complex interactions between crop and nonplant taxa that can be beneficial or antagonistic. There is also increasing demand for sustainable and environment-friendly solutions to manage pests and diseases, with the expectation that the biopesticide market share will increase to over 4.2% by 2010 and, for the first time, reach a market of over US$1 billion. Due to the rate of population increase the World Bank estimates that the global demand for food will double within the next 50 years. At the same time, the amount of arable land is decreasing from pressure from nonfarming activities and the unsustainable farming practices that are causing losses in soil fertility. This scenario is exacerbated by the fact that 40% of what is grown in the world is lost to weeds, pests, and diseases. In developing countries it is common for up to 70% of the yield to be lost due to attacks from insects and microbial diseases.

Therefore, agricultural production needs to be intensified and more marginal land used to produce sufficient food. This requires the deployment of improved land management techniques combined with the selection and distribution of appropriate crop and noncrop germplasm to exploit interactions with beneficial nonplant taxa and resist increased pressure from antagonistic nonplant taxa. Other factors such as climate change are likely to add new layers of complexity to these challenges. To predict risk and develop appropriate adaptation strategies, CGIAR and governments will become increasingly reliant on knowledge of and access to nonplant taxa genetic resources for food and agriculture. This will be used for research, training, or direct use in agriculture and originate, or be found, in a range of countries or centers.

Collections form the mechanism through which information and access to nonplant taxa can be obtained, but the survival of these collections is under threat from funding constraints. Appropriate policies, investments, and collaborations among CGIAR centers and with international collections are urgently needed to recognize noncrop taxa as global public goods. This would facilitate the conservation of collections, increase their visibility, and maximize their use for the benefit of sustainable farming systems. Especially in Africa, where the biodiversity is high, but the taxonomic and technological capacity is limited, work is needed to manage the full potential of nonplant taxa for food and agriculture.