Diversity: the spice of life

Sarah J. Hearne, s.hearne@cgiar.org

Cowpea seed collection, IITA genebank. Photo by IITA.
Cowpea seed collection, IITA genebank. Photo by IITA.

Cowpea is an important grain legume cultivated globally in the tree-scattered open grasslands of the tropics and subtropics. In Africa, these characteristic savanna regions are the “birthplace” of cowpea. The center of diversity of wild cowpea (where you find the most variation) is in southern and southeastern Africa; the center of diversity of cultivated cowpea is in West Africa (Padulosi 1993).

As a crop, cowpea is generally grown for its dry grain used for human and animal consumption, and green pods consumed as vegetables, and also for the fiber for textiles from the long peduncles or stalks (West Africa). It is a versatile plant and is used as a green manure, a dual-purpose crop in mixed cropping systems, and alone as a forage crop for livestock. The leaves are also eaten as a vegetable in parts of East Africa and in Senegal; in Sudan and Ethiopia, the roots are eaten as well.

IITA holds more than 15,000 accessions of cultivated cowpea in its genebank collection. These accessions form an invaluable resource for conservation and improvement. To be able to fully use such a collection, it is important to characterize the materials to enable the selection of the best materials for various purposes, such as crop improvement for high yield, better agronomic traits, drought tolerance, or disease resistance.

To help characterize IITA’s global cowpea collection, Institute scientists undertook a study funded by the Generation Challenge Program. This included defining a core collection from the thousands of accessions held in the IITA genebank, characterizing the molecular diversity of this collection, and defining a smaller reference collection to enable the wider use of these important genetic resources. Seeds of the core collection accessions were virus tested and have been made available for distribution.

A core collection is a subset of accessions that are representative of the diversity of the entire collection. These core collections are needed as they provide a smaller, more manageable number of materials from which meaningful conclusions reflecting the wider collection can be made. A core collection of 2,062 accessions was derived from the 15,000 accessions in the IITA genebank, based on information held on each accession within the genebank database. The core collection contains accessions from many countries but with more from West, East, and Central Africa—the cradle of cowpea diversity.

Cowpea collection sites
Cowpea collection sites

The core collection was then subjected to further study. Molecular markers, signposts present in the DNA of all living things, were used to look for variation among the accessions in the laboratory. Using the resulting data, scientists were able to describe the molecular diversity of the accessions and identify which accessions were more like one another and those that were not. As a result, clusters of accessions that were similar to one another could be identified. Altogether, nine such clusters were identified in the cowpea core collection.

The core collection is an important resource, but it is simply too large for many users of the genebank to apply in studies, such as screening for desired traits (perhaps disease resistance) in a systematic manner. It was therefore necessary to define from the core a smaller collection of accessions, called a reference collection. The reference set of 374 accessions was defined using the clusters identifed in the molecular characterization. The reference collection is representative of the molecular diversity and descriptive diversity of the core and the entire collection.

As soon as the definition of the cowpea reference collection was publicized the genebank received many requests for the materials. The reference collection has been used widely by IITA scientists and our many partners and genebank clients in studies looking at drought, pest and disease tolerance, and in further studies of molecular diversity. The robustness of the collection was confirmed during some of these studies when comparisons of the reference collection with those from other institutes indicated that there was no novel molecular diversity present in the other collections investigated.

Reference
Padulosi, S. 1993. Genetic diversity, taxonomy, and ecogeographic survey of the wild relatives of cowpea (V. unguiculata). PhD thesis. University of Louvain La Neuve, Belgium.

Safeguarding local varieties ensures food security

Cassava pile after harvest. Photo by IITA.
Cassava pile after harvest. Photo by IITA.

Cassava is a food security crop to more than 600 million people in the developing world, providing incomes to resource-poor farmers, improving their livelihoods, and serving as a buffer against food crises.

The strategic importance of cassava, however, is being threatened, especially in Africa, as local varieties are in danger of disappearing because of genetic erosion and other human and natural factors.

“In Guinea, for instance, about seven local cassava varieties are fast disappearing. This is risky, especially for cassava since it is a clonal crop,” according to Paul Ilona, IITA Senior International Trials Manager. Clonal crops are those propagated through cuttings or other plant parts, not by seeds.

Genetic erosion is a process whereby the already limited gene pool of an endangered species of plant or animal diminishes even more when individuals from the surviving population die out without getting a chance to breed within their endangered low population.

Both local and improved cassava varieties alike create a robust gene pool, offering choices for breeders in future breeding programs. However, the loss of genes from the extinction of some local varieties could limit future improvement programs. The endangered varieties may hold key traits that could offer possible solutions to hunger and poverty in the future.

Woman selling cassava, local market, Nigeria. Photo by IITA.
Woman selling cassava, local market, Nigeria. Photo by IITA.

To prevent the genetic erosion of cassava, IITA and the Institut de Recherche Agronomique de Guinée (IRAG) have stepped up efforts to save native African varieties with the collection of 73 local varieties from Guinea, West Africa.

These varieties are now conserved under ex situ conditions at IITA’s Genetic Resources Center (GRC) in Ibadan, Nigeria. They form part of a collection to safeguard the continent’s plant genetic resources. The collecting mission in that West African country last year was funded by the Global Crop Diversity Trust (GCDT), IRAG-Guinea, and IITA.

“The conservation of local varieties provides hope for future cassava breeding programs and helps to guarantee food security in Africa,” says Dominique Dumet, GRC Head and coordinator of the collecting mission.

Ilona says the loss of native cassava varieties might limit the number of genes available for breeders to work with. “For breeders, any time we lose (crop) genes, it hurts. That is why the conservation of local cassava varieties at GRC is important to us,” he says.

Apart from cassava, the IITA-GRC holds over 25,000 accessions of major African food crops, including cowpea, yam, soybean, bambara nut, maize, and plantain/banana. IITA shares these accessions without restriction for use in research for food and agriculture.

The collecting mission makes Guinea the fourth country, after Angola, Togo, and Bénin, to allow IITA to collect and share their germplasm with other countries, since the International Treaty on Plant Genetic Resources for Food and Agriculture went into force in June 2004.

Unraveling the diversity of African insects

“A problem identified is half-solved.” — Anonymous

The IITA insect center in Bénin houses one of the largest reference collections of arthropods and microorganisms in West Africa. An insect identification hub, it plays the role of a “gatekeeper” by facilitating the discovery and monitoring of invasive pests in the region. The resulting information helps to locate the probable area of origin where promising natural antagonists may be found.

Entomologist Georg Goergen, IITA-Benin
Entomologist Georg Goergen, IITA-Bénin. Photo by IITA

Several invasive insect pests have recently been identified by the center, among which are fruit flies, whiteflies, and moths. An example was when a myriad of caterpillars and moths invaded Liberian farms early this year, providing entomologists a puzzle. The identity of this pest that devastated crops and contaminated water supply in northern Liberia had been established through the joint efforts of FAO, IITA, and CABI. It was later identified as Achaea catocaloides by Georg Goergen, IITA entomologist and biosystematist. The insect is a member of the Lepidoptera group and known as a fruit-sucking moth.

Goergen says that proper identification is a starting point for any basic or applied research and a prerequisite for any successful biocontrol program. “Any biocontrol approach without proper identification of the insect pests will fail,” he says.

Rapidly accelerating human trade, transport, travel, tourism, and porous borders have dramatically contributed to the introduction, ease of movement, and spread of invasive pests thereby overwhelming the capacities of quarantine services in West Africa.

IITA works with national and international partners to control the spread of these invasive species. In addition to its role of identifying insects, the center is also helping scientists to unravel and conserve the rich diversity of African insects.

Through the identification of insect specimens, scientists get more insight on the species richness of the African insect diversity in various ecosystems, the structure of their populations, their interrelationships, and interactions with their habitats.

Insect collection, IITA Benin
Insect collection, IITA Bénin. Photo by IITA

Insects represent the majority of living organisms, accounting for about two-thirds of all living animals on earth and filling many niches in both terrestrial and aquatic ecosystems. They thus play an important regulatory role in all ecosystems including agricultural environments. Many of them can become notorious pests of agricultural, medical, and veterinary importance.

However, existing knowledge on insect diversity is still inadequate for large parts of the globe and no one knows exactly how many species of insects exist. The situation is worse in Africa where much of the planet’s biodiversity occurs, but where traditionally the scarcity of biosystematists is the strongest.

Goergen says, “Biosystematics is important in all phases of a control program starting from a reliable pest identification, assessment of native antagonists, monitoring faunal changes following the use of exotic beneficials, and detection of eventual nontarget effects. To do that, you need to have a reference collection such as the one we have here in Cotonou.”

IITA has developed a strong regional capacity in biosystematics through the West African Network for Taxonomy, BioNET-INTERNATIONAL.

The center continues to attract students from different parts of the world while offering capacity building and ensuring a requisite contribution to countries seeking to comply with the sanitary and phytosanitary agreement of the World Trade Organization and to fulfill the objectives anchored in the Convention on Biological Diversity.