Joining hands to fight the legume pod borer

Manuele Tamò,

Maruca vitrata larva affected by the entomopathogenic virus MaviMNPV. Photo by S. Srinivasan, AVRDC.
Maruca vitrata larva affected by the entomopathogenic virus MaviMNPV. Photo by S. Srinivasan, AVRDC.

A new collaborative project has been launched to develop novel approaches against an old problem affecting cultivated legumes—the pod borer Maruca vitrata.

This is one of the major pests of cowpea in West Africa, where, if left uncontrolled, it can lead to 80% yield losses.

Under this new project, funded by the German Federal Ministry for Economic Cooperation (BMZ), IITA and partners, the World Vegetable Center (AVRDC), and the International Center for Insect Physiology and Ecology (icipe), will test a range of new natural enemies against the legume pod borer. In close collaboration with national agricultural research systems (NARS) and scientists and colleagues in the Plant Protection and Quarantine Services, the project will choose the most promising natural enemies adapted to West and East African conditions.

One of the major outcomes of this project will be to quantify the impact of selected biocontrol agents on the population ecology of the pod borer and on cowpea yield in the field. At the same time, detailed molecular analysis of pod borer populations from different parts of the tropics, Africa, South America, and Asia, in collaboration with the BMZ project and a Dry Grain Pulses Collaborative Research Support Program (DGP-CRSP) project with the University of Illinois, will permit the identification of scoreable polymorphisms for determining the genetic similarity and differences between pod borer populations at distant locations. This will enable project staff to answer questions in relation to differential responses to synthetic pheromones, the diversity of biocontrol agents, and the development of an insect resistance management plan in preparation for the deployment of Bacillus thuringiensis (bt) cowpea in the region.

Experimental release of Apanteles taragamae using caged Sesbania cannabina. Photo by M. Tamo, IITA.
Experimental release of Apanteles taragamae using caged Sesbania cannabina. Photo by M. Tamo, IITA.

Prior to this new project, AVRDC and IITA have already collaborated, both formally and informally, on research on pod borer control. Biodiversity studies carried out at AVRDC in Taiwan had identified the exotic parasitoid Apanteles taragamae as the most promising candidate. This was subsequently introduced into the laboratories of IITA Bénin station. After a series of pre-release tests, experimental inoculative releases of A. taragamae were carried out between February and June 2007 in Bénin, Ghana, and Nigeria. The sites were patches of wild vegetation including plants known to host the pod borer, such as the legume trees Lonchocarpus sericeus, Pterocarpus santalinoides, and the shrubs Lonchocarpus cyanescens and Tephrosia spp.

As early as 6 months after the first releases IITA started a series of surveys to monitor the establishment of the parasitoid in the neighborhood of the releases. The monitoring continued until 2009, during which time we were not able to recover the parasitoid. However, we found indirect evidence of establishment in the environment (see below). We ruled out the theory that interspecific competition with indigenous parasitoids exploiting M. vitrata larvae of the same age and on the same host plant was the cause for this lack of evidence. We had conducted, just before the releases, quite elaborate competition studies which did not reveal any problems. Also, in its area of origin in Taiwan, A. taragamae coexists with similar parasitoid species found in Bénin, e.g., Phanerotoma sp. and Dolichogenidaea sp.

In Taiwan, however, A. taragamae is found prevalently on the cover crop Sesbania cannabina. This has been difficult to grow in West Africa because of foliage beetles (particularly Mesoplatys sp.) that completely defoliate the plant. We also intensified our studies on African indigenous species of Sesbania which suffer less beetle damage. So far, there have been no signs of direct establishment, although screenhouse experiments have confirmed the suitability of Sesbania spp. both as a feeding substrate for the pod borers and as a host for foraging parasitoids.

More recently, with funds from DGP-CRSP, we have developed a new release system using caged S. cannabina, infested artificially with eggs of M. vitrata, and subsequently inoculated with adult A. taragamae. Preliminary results indicate that such a cage can produce up to 300 cocoons of the parasitoid. At this stage, the cage can be removed and the parasitoids can emerge from the cocoons and disperse in the surrounding natural habitat. This deployment system is currently under testing in Bénin.

Adult female of Maruca vitrata. Photo by G. Goergen, IITA.
Adult female of Maruca vitrata. Photo by G. Goergen, IITA.

Another important beneficial organism which was identified by AVRDC in Taiwan is the Maruca vitrata Multi-Nucleopolyhedrosis Virus (MaviMNPV). This was imported to IITA-Bénin for further assessment. Again, after a series of laboratory tests which confirmed the results obtained in Taiwan and ascertained the specificity of MaviMNPV to the target host, IITA proceeded to test the virus in seminatural conditions. For this, we used field cages with artificial infestations of M. vitrata larvae. These experiments were also replicated in the screenhouse in Kano, Nigeria. Both tests indicated a very high mortality of pod borer larvae (>95%) using standard concentrations comparable to those found in commercial formulations of entomopathogenic viruses (e.g., against the cotton bollworm Helicoverpa armigera).

In Bénin, we did not carry out any open field experiments, so we were puzzled to discover a few pod borer larvae collected in the Mono region, close to release sites of the parasitoids, with apparent signs of the virus (Note: MaviMNPV had never been found in Bénin nor anywhere else in West Africa prior to the introduction in 2007, as confirmed by surveys of Dr A. Cherry in collaboration with the Natural Resources Institute).

Based on this discovery, and also aided by literature support, we attempted to verify the hypothesis that the parasitoid A. taragamae could have transmitted the virus MaviMNPV to pod borer larvae. We used three different infection methods (ovipositor only, whole body without ovipositor, and indirectly through artificial diet) to test the hypothesis. Results confirmed that the parasitoid was able to transmit the virus to the larvae through any of the infection methods. This discovery is quite significant: the parasitoid may be able to spread the virus in the environment without any further intervention.

This is also indirect evidence that A. taragamae is present in the environment, maybe at low levels, that cannot be detected by current sampling methods, or on secondary host plants for M. vitrata whose identity is still unknown. Further studies indicated that A. taragamae females can pass on the virus up to the third generation.

At present, we are looking for low-cost and efficient ways of producing the parasitoid and the virus so that the technology can be implemented by NARS colleagues and cottage industries at the community level, with financial support from DGP-CRSP. Also, training and demonstration videos of the major cowpea pests, their natural enemies, and detailed rearing methodologies are being prepared.

Improved cowpea varieties for Nigeria’s savannas

Nigeria has released two new cowpea varieties to raise production and improve farmers’ incomes.

Harvesting cowpea. Photo by IITA
Harvesting cowpea. Photo by IITA

The varieties—IT89KD-288 and IT89KD-391—were developed by scientists working at IITA, Ibadan, in collaboration with the Institute for Agricultural Research of the Ahmadu Bello University, Zaria; University of Maiduguri, Borno; and the Agricultural Development Programs of Borno, Kaduna, Kano, and Katsina States.

Both varieties have proven to be superior over the current improved lines being cultivated. They could be used to overcome the challenges faced by cowpea farmers in the country.

For instance, IT89KD-288 (now SAMPEA-11) is a dual-purpose cowpea variety with large white seeds and a rough seed coat. It has combined resistance to major diseases including septoria leaf spot, scab, and bacterial blight, as well as to nematodes, and tolerance for Nigeria’s strain of Striga gesnerioides (a parasitic weed that severely lowers yield).

“It also has a yield advantage of at least 80% over the local varieties,” said Alpha Kamara, IITA Agronomist, who is leading efforts to rapidly disseminate the varieties to farmers.

The nematode-resistant variety is an equally good candidate for sowing with cereals or as a relay crop with maize in the moist and dry savanna zones, and for high grain production in the dry season.

Scientists recommend that the variety be planted in mid-July in the Sudan savanna, early to mid-August in the northern Guinea savanna, and by the end of August in the southern Guinea savanna. However, if there is certainty of rains up till the end of October, IT89KD-288 can be planted in September.

Cowpea farmers in Kano, Nigeria. Photo by IITA.
Cowpea farmers in Kano, Nigeria. Photo by IITA.

IT89KD-391 (now SAMPEA-12) is also a dual-purpose cowpea variety but it has medium-to-large brown seeds with a rough seed coat. These are preferred seed characteristics for commercial production in northeast Nigeria.

“IT89KD-391 is a welcome improvement over SAMPEA 7, Ife brown, IT90K-76, and IT90K-82-2 which are the main improved brown-seeded varieties available. It has been tested extensively in this area and is well accepted by the farmers,” said Hakeem Ajeigbe, IITA Extension/Dissemination Specialist.

“The variety performs well as a sole crop and an intercrop. It could also be planted as a relay crop with maize in the Guinea savannas,” he added.
Several on-station and on-farm trials have shown that IT89KD-391 (SAMPEA 12) produces double the yields of local cultivars.

In 2008, Nigeria released a Striga-resistant improved cowpea variety (IT97K-499-35).

“The demand for these improved varieties is high because of their superior yields and their acceptability by consumers,” Kamara said.

The quiet revolution

B.B. Singh,

Cowpea was a relatively minor tropical legume about 50 years ago, but it is now emerging as one of the most important food legumes in the 21st century because of its early maturity and ability to fit as a niche crop in multiple cropping systems. There has been more than a 6-fold increase in the world cowpea production in the last few decades—a quiet revolution that is greater in magnitude compared to that of cereals and all other pulses.

Women farmers growing 60-day cowpea in Nigeria. Photo from B.B. Singh.
Women farmers growing 60-day cowpea in Nigeria. Photo from B.B. Singh.

Based on FAO data and correspondence with scientists in different countries, annual cowpea production has increased from about 0.87 million tons in 1961 to 1.2 million tons in 1981 to 2.4 million tons in 1991, to more than 6.3 million tons in 2008. The major increases have been in Niger, Nigeria, Mali, Burkina Faso, Senegal, Tanzania, Uganda, Congo, Myanmar, India, and Brazil. These successive increases in cowpea production over time have occurred due to the concerted efforts and coordinated cowpea research and development activities of IITA and its national, regional, and international partners over the last four decades and the release of new improved short-duration cowpea varieties in different countries.

It is expected that cowpea production will significantly increase in the coming decades also as more short-duration and pest-resistant varieties become available and cowpea cultivation makes further inroads as a niche crop in the cereals and root crops-based systems.

Improved 60-day cowpea in northern Nigeria. Photo from B.B. Sungh.
Improved 60-day cowpea in northern Nigeria. Photo from B.B. Sungh.

Significant advances in cowpea research
Cowpea originated in the southern African region several thousand years ago and spread to the different parts of the world covering over 65 countries in Asia and Oceania, the Middle East, Southern Europe, Africa, Southern USA, and Central and South America. The nitrogen-fixing crop with great versatility was entrenched into local cropping and food systems. It was given indigenous names such as ‘lobia’ in India, ‘kunde’ in east Africa, ‘beans’ and ‘wake’ in Nigeria, ‘niebe’ in francophone Africa, ‘southern pea’ and ‘blackeye pea’ in the USA, ‘feijão caupe’, in Brazil, and a host of other names in different countries around the world.

Its nutritious young leaves, green pods, green seeds, and dry grains are used in various food preparations, while the nutritious fodder is fed to livestock and the crop residue in the field contributes to improved soil fertility.

Limited efforts in cowpea improvement began in a few countries in the 1960s but it was the establishment of IITA in 1967 that gave cowpea some well-deserved attention. IITA actively collaborated with its NARS partners in catalyzing and supporting research on cowpea improvement and distributing improved cowpea materials.

Cowpea research received another boost when the USAID-funded Bean/Cowpea CRSP (now The Dry Pulses Project) became operational in the 1980s as it complemented IITA’s efforts in strengthening cowpea research and development in Africa. The recently established Network for Genetic Improvement of Cowpea for Africa (NGICA) has further strengthened cowpea research in the region.

The major successes include a collection and use of over 15,000 germplasm lines and development of a range of improved varieties with diverse maturity, plant type and seed type combined with high protein, iron, zinc, and resistance to major biotic and abiotic stresses. Using a combination of field and laboratory screening, several varieties have been developed with combined resistance to cowpea yellow mosaic, blackeye cowpea mosaic, and many strains of cowpea aphid-borne mosaic, Cercospora, smut, rust, Septoria, scab, Ascochyta blight, bacterial blight, anthracnose, nematodes, Striga, Alectra, aphid, thrips, and bruchid.

Similarly, using simple screening methods for tolerance for heat, drought, and low P, major varietal differences for all the three traits have been identified and incorporated into improved varieties. Also, varieties with 30% protein and enhanced levels of iron, zinc, and other micronutrients have been identified.

Joint efforts are being made by IITA, The Dry Pulses project, advanced laboratories in the USA and Australia, African Agricultural Technology Foundation (AATF), NGICA, and Monsanto Corporation to exploit biotechnological tools and complement conventional methods for improving insect resistance in cowpea. Efforts are also under way to develop markers and protocols for marker-assisted selection (MAS) for Striga resistance and other traits in cowpea.

Development and release of improved varieties
Using the vast genetic pool and useful genes already identified, a great deal of progress has been made in breeding a range of high-yielding cowpea varieties with combined resistance to major diseases, insect pests, Striga and Alectra, and drought tolerance. Combining erect plant type with early maturity and resistance to major pests, several new extra-early cowpea varieties have been developed which yield up to 2 t/ha within 60 days compared to <1 t/ha in local varieties, which mature in 100 to 140 days.

Similarly, several medium-maturing dual-purpose varieties have been developed which yield over 2.5 t/ha grain and over 3 t/ha fodder in 75–80 days. These varieties have been tested and based on their good performance, over 40 improved varieties have been released in 65 countries covering Africa, Asia, and Central and South America.

The new varieties have been given specific and interesting names such as ‘Big Buff’ (IT82E-18) in Australia; ‘Bira’ (TVx 3236) in Angola; ‘Titan’ (IT84D-449) and ‘Cubinata’ (IT84D-666) in Cuba; ‘Asontem’ (IT82E-16), ‘Ayiyi’ (IT83S-728-13), and ‘Bengpla’ (IT83S-818) in Ghana, ‘Akash’ (IT82D-752) (sky) and ‘Prakash’ (IT82D-889) (light) in Nepal; ‘Sosokoyo’ (IT84S-2049) in Gambia; ‘Pkoko Togboi’ (IT85F-867-5) in Guinea Conakry; ‘Korobalen’ (IT89KD-374) and ‘Sangaraka’ (IT89KD-245) in Mali; ‘Dan IITA’ (TVx 3236) (son of IITA) and ‘Dan Bunkure’ (IT89KD-288), IT90K-76, IT90K-82-2, IT90K-277-2, and IT93K-452-1, in Nigeria; ‘Melakh’ and ‘Mouride’ in Senegal; ‘Pannar 31’ (IT82E-16) in South Africa; ‘Dahal Elgoz’ (IT84S-2163) (gold from the sand) in Sudan; ‘Umtilane’ (IT82D-889) in Swaziland; and ‘Bubebe’ (IT82E-16) in Zambia; ‘Vamban 1’ (IT85F-2020), ‘Pant Lobia-1’ (IT98K-205-8), and ‘Pant Lobia-2’ (IT97K-1042-3) in India; and many more.

Improved cowpea-sorghum strip cropping system. Photo from B.B. Singh.
Improved cowpea-sorghum strip cropping system. Photo from B.B. Singh.

Cereals-cowpea intensive cropping systems in the tropics
With support from USAID, UK Department for International Development (DFID), GATSBY Foundation, Danish International Development Agency (DANIDA), Canadian International Development Agency (CIDA), and others, several improved intensive cowpea-cereals cropping systems have been developed. The improved strip cropping system involving two rows of cereals and four rows of cowpea has enabled farmers in Nigeria and Niger to produce one to two cowpea crops in the same season while maximizing the cereal yields.

Similarly experiments conducted using 60-day cowpea varieties in northern Nigeria and India have demonstrated successful triple cropping involving ‘wheat-cowpea-rice’ each year. The additional cowpea crop in the summer season after the wheat harvest not only provides extra employment but it also improves soil fertility and provides nutritious food grain and fodder.

60-day cowpea in wheat-rice system in northern India. Photo from B.B. Singh
60-day cowpea in wheat-rice system in northern India. Photo from B.B. Singh

Future outlook
In the wake of increasing global warming and declining rainfall and water table, it is expected that cowpea production will increase in the future using heat- and drought-tolerant 60-day cowpeas as a niche crop in the cereals and root crops systems covering millions of hectares in Asia, Africa, and the Americas. Northern India alone has about 10 million ha under wheat-rice system. An additional crop of 60-day cowpeas as a niche crop between wheat and rice can produce between 10 to 15 million t of cowpea which would double the current pulses production in India.

A similar possibility exists for double cowpea cropping in several parts of Africa and wheat-cowpea double cropping in southern United States covering several million hectares. Brazil is adding thousands of hectares of new land each year under cowpea cultivation.

Thus, there is a need to develop a diverse set of region-specific and niche-specific varieties to expand cowpea cultivation in the world and help improve family food security and nutrition.

Contact details:
B.B. Singh, Visiting Professor
Department of Soil and Crop Sciences,
Texas A&M University, College Station, TX 77840, USA

Anyone for cowpea?

Improved cowpea variety. Photo by IITA.
Improved cowpea variety. Photo by IITA.

The cowpea is not actually a pea but a little bean that has a huge range of remarkable attributes and properties. Despite being a staple food to millions of people, this unassuming crop does not have the global profile it deserves.

Did you know that the cowpea is actually one of the oldest domesticated crops known to the human race? It is believed to have originated in West Africa between five and six thousand years ago where it was associated with ancient cereal farming. From Africa it was taken around the world by merchants, travelers, and most notably by slaves. Between the 16th and 19th centuries, millions of people were transported across the Atlantic. Many of them ended up in the southern United States. The cowpea was brought with them and became a staple of African American cookery, which is often called “soul food”.

Today the cowpea is grown on over 10.1 million ha across the globe (FAO 2008). Africa produces almost 5.2 million t of the global total of 5.4 million t of dried cowpea. Nigeria is the world’s largest producer, generating 58% of the worldwide yield.

The cowpea is rich in several vitamins, minerals, and especially protein, which makes it a key crop in poverty-stricken areas because it can be used as a replacement for meat. More than 4 million t of cowpea are consumed worldwide each year. In Africa alone, 387,000 t are eaten.

In East Africa, the leaves are often used rather like spinach, in soups and stews. In Asia and Latin America, the green seed pods, similar to runner beans, are eaten as a vegetable. The seeds, though, are the main food product from the cowpea plant. They can be dried, used fresh, or cooked, then canned or frozen. The beans are often served with rice but can also be added to other meals. In Nigeria, cowpea is used to make akara, a savory fried donut and moin-moin, a steamed bean cake.

However, it is not only humans that enjoy the crop. The plants are also used as animal fodder. The stems, leaves, and vines can be harvested and given to livestock fresh but are more commonly dried and turned into hay or silage. In West Africa, cowpea hay is a significant source of income for farmers during the dry season.

On top of being an incredible food product, cowpea is resistant to drought and easily adapts to different soils while growing intercropped with other plants, such as yam, maize, or millet. This makes the crop easy to grow, even for small-scale farmers. As a legume, cowpea acts as a green manure, replenishing the nitrogen in the soil and increasing land fertility. The crop also maintains the land by growing quickly and covering fields, deflecting the rain with the leaves, and preventing erosion.

Cowpea market vendor, Ibadan, Nigeria. Photo by IITA.
Cowpea market vendor, Ibadan, Nigeria. Photo by IITA.

It’s not all plain sailing for the versatile cowpea. Pests, such as aphids and bruchid weevils attack the cowpea plant during its life cycle; it is also damaged by bacteria, fungi, and viruses that cause diseases such as Cercospora leaf spot, a fungal infection on the leaves. Other problems that the cowpea can face come from nematodes in the ground that inhibit the roots and parasitic weeds that grow up around the plant and eventually choke it.

IITA and its partners have made a significant breakthrough with this plant. They have created varieties with better disease and pest resistance and some with consumer-preferred traits, such as being easier and faster to grow, high yielding, and having seeds of a specific size, texture, or color. In addition there are varieties that actually shorten the processing because they are easier to cook and peel. These modified varieties have been distributed to over 68 countries across the globe.

IITA has also made major steps in collecting and categorizing the world’s largest collection of cowpea germplasm in its genebank. The diverse collection represents 70% of African examples and just under half of those found globally.

At the Fifth World Cowpea Research Conference, taking place in Senegal from 27 September to 1 October 2010, scientists from around the world will meet to tackle various issues surrounding the crop. Not least of these is to promote the versatile cowpea from being a less well-known extra to a main player on the world stage. So, anyone for cowpea?


All about the bag

Dieudonne Baributsa,

Women observing cowpea stored in PICS bags after the open-the-bag event. Photo from D. Baributsa, PICS.
Women observing cowpea stored in PICS bags after the open-the-bag event. Photo from D. Baributsa, PICS.

Farmers throughout West and Central Africa call it the “magic bag”—the triple layer bag developed by Purdue University and partners to control the cowpea bruchid Callosobruchus maculatus. The bag does not use any of the chemicals that are so often misused, or overused, causing the health hazard commonly referred to as “killer bean” in Nigeria. The technology is being widely adopted because it is simple, easy to use, effective, and profitable to farmers and other users.

Professor Larry Murdock led a team composed of the Purdue University faculty, students, and other partners to initiate the development of this technology in the late 1980s with funds from the Bean/Cowpea Collaborative Research Support Program (CRSP). In 2007, with funding from the Bill & Melinda Gates Foundation under the Purdue Improved Cowpea Storage (PICS) project (, the technology was refined and is being disseminated in 10 countries in West and Central Africa: Nigeria, Niger, Burkina Faso, Mali, Togo, Bénin, Ghana, Cameroon, Chad, and Senegal.

The PICS project has two thrusts: outreach activities that are expected to reach around 28,000 villages, and supply chain development. The project has just entered its fourth year.

Outreach activities have been implemented in collaboration with IITA, World Vision International, National Institute for Agricultural Research of Niger (INRAN), National Institute for Agricultural and Environmental Research (INERA) of Burkina Faso, Institute of Agricultural Research for Development (IRAD) of Cameroon, national extension systems in various countries, farmers’ associations, and NGOs. To date, the technology has reached more than 23,000 villages in Nigeria, Niger, Mali, Burkina Faso, Togo, and Bénin. The project has recently launched activities in the four remaining countries (Senegal, Ghana, Cameroon, and Chad) with the completion of the training for field technicians.

Young men carrying cowpea in triple layer bags to their village, Lankoue, Burkina Faso. Photo from D. Baributsa, PICS.
Young men carrying cowpea in triple layer bags to their village, Lankoue, Burkina Faso. Photo from D. Baributsa, PICS.

The PICS project is also developing a supply chain system for the triple layer sacks in West and Central Africa. The development of this system is providing business opportunities for manufacturers of sacks, distributors, and vendors. The PICS project has worked with five manufacturers of plastics in five West African countries to produce over 1.25 million bags. In addition, Purdue has worked with local entrepreneurs to sell the storage technology through their distribution networks so that it is easily available to farmers.

More than 100,000 PICS bags have been used in village demonstrations. The technology has proved to be effective. Cowpea in all of the PICS bags were as good during the open-the-bag events (in April and May) as they were at harvest time (October and November), except for the occasional bag that had been damaged by rodents or accidentally pierced.

Communication has been a major part of the PICS efforts. Radio, print media, TV, and cell phone videos have been used to build awareness about the triple layer technology. Messages in local languages have been effective in communicating the technology to farmers and other users. Research by Purdue University has determined that the radio is key and effective in reinforcing the PICS technology message in rural villages. Print media, such as posters and flyers on “fiche techniques,” are also being disseminated in local languages. TV spots on the technology have been broadcast in some areas, but few in rural West and Central Africa have access to TV.

PICS poster, Wolof/Senegal
PICS poster, Wolof/Senegal

The PICS project is taking advantage of the use of cell phones with Bluetooth, a wireless communications technology that facilitates data transmission over short distances, in rural communities to disseminate video clips describing the use of the PICS technology.

Hermetic sealing is difficult to describe in words on the radio or in print, but many people immediately understand it if they see it demonstrated. To facilitate visual learning on the use of hermetic storage, the PICS project developed cell phone videos in Hausa (Niger and Nigeria), French (Niger and Cameroon), Fulfulde (Cameroon), and English (Nigeria). An assessment of the PICS cell phone video dissemination showed its potential as an effective means of conveying extension messages to farmers.

Women’s participation has also been at the forefront of PICS activities. A goal was set of 30% participation and this has significantly increased the number of women involved in both field staff training and village activities. Several strategies have been used to reach this goal, including recruiting female field technicians to conduct training for women in areas where mixed gender gatherings are not allowed, competitions for women about cowpea, and other approaches.

The PICS project is currently seeking ways to expand the use of the triple layer bag to store crops other than cowpea.

Diversity: the spice of life

Sarah J. Hearne,

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.

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.

Cowpea and other Vigna species in Serbia

Aleksandar Mikić (, Mirjana Milošević, Vojislav Mihailović, Charassri Nualsri, Dušan Milošević, Mirjana Vasić, and Dušica Delić

A cowpea accession in the field evaluation of forage yields in Novi Sad, Serbia. Photo by A. Mikic.
A cowpea accession in the field evaluation of forage yields in Novi Sad, Serbia. Photo by A. Mikic.

Serbia and other countries of the northern and western parts of the Balkan Peninsula have a typical temperate continental climate. The most important grain legume crop here is soybean (Glycine max (L.) Merr.) with an advanced native breeding program carried out in the Institute of Field and Vegetable Crops in Novi Sad. The most widely used pulse is the Phaseolus bean that has almost completely replaced traditional varieties, such as faba bean (Vicia faba L.) or lentil (Lens culinaris Medik.). The pea crop (Pisum sativum L.) retained its place both for human consumption and in animal feeding. Vetches (Vicia spp.) are used as both a forage and green manure crop.

Cowpea (Vigna unguiculata (L.) Walp.) is not completely unknown in the Balkans, with several Serbian/ Croatian words denoting this crop. Often it is called simply vigna, as the whole genus, or prava vigna (true vigna), to distinguish it from the other related species. There are also descriptive names, such as crnookica (black-eyed one) and kravlji pasulj (cow bean). Another name, mletački grašak (Venice pea) suggests that this species was most likely introduced into the Balkans from northern Italy.

Cowpea was distributed in the coastal regions of Croatia, one of the countries that formed the former Yugoslavia, where the Italian cultivar “Cremonese” showed very good results when grown both as a pure stand and in mixtures with Sudan grass, sorghum, and maize.

Today, cowpea has remained a rather neglected and underutilized crop in Serbian agriculture. Only one cowpea cultivar named “Domaća”, of uncertain origin, was included in the official Serbian cultivar list. Cowpea may be found, rather sporadically, along with various market classes of common bean (Phaseolus vulgaris L.), especially in the valley of the Morava river in central Serbia. Local people usually refer to it as pasuljica (little common bean), not really distinguishing it from various types of common bean. Like these, cowpea is used as a vegetable in diverse forms and is grown mainly in gardens.

Recently, along with the introduction of new trends such as the preference for healthy food, it is possible to buy adzuki bean (Vigna angularis (Willd.) Ohwi & H. Ohashi), mung bean (Vigna radiata (L.) R. Wilczek), and black gram (Vigna mungo (L.) Hepper), mostly of Chinese origin. These are used as pulses.

The genetic resources of cowpea and other Vigna species in Serbia are maintained mainly in the Institute of Field and Vegetable Crops, with its Vegetable Crops and Forage Crops Departments, as well as in the Institute of Soil Science, with a total of some 30 diverse accessions.

Since 2004, an evaluation of the most important agronomic traits in cowpea and other Vigna species has been initiated within the field trials in the Institute of Field and Vegetable Crops, at 45°20′ N, 19°51′ E and 84 m asl. As typical warm-season annual legumes, cowpea and other Vigna species were sown in late April. The preliminary results of the trial with cowpea grown for grain were presented at the 4th World Cowpea Congress in Durban in 2005 (Table 1). The most important conclusion from this evaluation was that the short day length in some accessions was the major reason for their inability to produce seeds before the first winter frosts in October.

The next step in testing cowpea potential in the conditions of Serbia was to evaluate its forage yields. It is possible to select the lines that could be developed into proper dual-purpose cultivars, with reliable yields of both grain and forage (Table 2).



The evaluation of the cowpea accessions continues along with the evaluation of the adzuki and mung bean that has also brought promising results.

Due to its multipurpose nature, cowpea could be reintroduced into the agriculture of Serbia and other southeast European regions in several ways. An improvement could be made by developing vegetable cultivars for both garden use, with a longer growing period and prolonged maturity, and field production, with prominent earliness and uniform maturity.

An intercropping of mung bean with soybean for forage production, Belgrade, Serbia. Photo by A. Mikic.
An intercropping of mung bean with soybean for forage production, Belgrade, Serbia. Photo by A. Mikic.

As a forage crop, cowpea may play a very important role in providing farmers with fresh forage during the summer months, when the pea crop or vetches have long gone from the fields. However, breeding cowpea for forage production must provide not only good, high quality forage yields, but also reliable seed yields, enabling a newly-developed forage cowpea cultivar to survive in the market. All this emphasizes the importance of selecting the genotypes with an appropriate photoperiodical reaction.

In 2009, the trials started with mutual intercropping of annual legumes for forage production. Cowpea, adzuki, mung bean, and black gram, with poor standing ability, were deliberately mixed with soybean that acts as a supporting crop. Preliminary results showed that mixtures with cowpea may produce more than 40 t/ha of green manure with a Land Equivalent Ratio (LER) higher than 1, proving its economic reliability.

The first step towards international cooperation in cowpea research involving Serbia is a project with the Prince of Songkla University, aimed at collecting cowpea landraces in Thailand and their complex evaluation in contrasting environments.

Enriching livestock diets with cowpea

Loaded on camel-back, covering roofs, stored in tree tops, and traded in the market, cowpea haulms can be seen throughout the semiarid tropical regions being stored, marketed, and used as livestock feed. Expanding the intensification of crop−livestock systems encourages the use of dual-purpose cowpea varieties that produce high yields of both grain and fodder.

Farmer feeding sheep with cowpea haulms. Photo by ILRI.
Farmer feeding sheep with cowpea haulms. Photo by ILRI.

Research on yield and quality of cowpea haulms by centers belonging to the Consultative Group on International Agricultural Research is leading to improvements in livestock production and the associated incomes of crop−livestock farmers.

Cowpea is an important component in mixed crop−livestock systems in the semi-arid regions of the tropics. It is being grown more and more to provide high levels of fodder for livestock in addition to producing grain for people. Since the late 1980s, cowpea breeding programs have worked toward producing dual-purpose varieties that emphasize the production of grain and fodder resulting in varieties that can yield over 1 t/ha of grain and 2 t/ha of fodder.

Crop residues—the stalks, stems, and leaves remaining after seed harvest—make up a major component of livestock diets in mixed crop−livestock systems. Improving the nutritional quality of crop residues is thus important to enhance the productivity and profitability of these farming systems. Demand for livestock products through much of the semi-arid tropics will be likely to continue to increase along with the use of purchased feedstuffs. For this reason, sales of cowpea fodder have been expanding, providing cowpea farmers with additional opportunities for marketing their surplus crop.

Late-maturing varieties of cowpea are often used for fodder because they can take advantage of a longer growing season to amass more biomass. Where the longer growing period can make the crop susceptible to late drought, varieties may be preferred with a high fodder yield produced within a more moderate growing period. A collaborative program between IITA and the International Livestock Research Institute (ILRI), which was started in the 1980s to evaluate and develop dual-purpose varieties, has produced several that have become well accepted when tested on-farm.

Woman farmer tending to her goat. Photo by ILRI.
Woman farmer tending to her goat. Photo by ILRI.

It is useful to know the differences in performance of livestock fed on different varieties of cowpea. Some varieties have been tested for their ability to increase the weight of small ruminants or improve the milk yield of cows. However, only a few varieties can be compared at one time in live animal trials. This makes the systematic screening of cowpea genetic resources important for advancing the development of dual-purpose varieties.

Screening tools that can rapidly assess the nutritional quality of different varieties greatly aid the evaluation process. Near-infrared reflectance spectroscopy (NIRS) is one such tool, allowing the fast and inexpensive analysis of small quantities of plant biomass. This technique uses near-infrared light to measure nutritive quality, such as the amounts of nitrogen and fiber, or the digestibility of the fodder, all of which are related directly to animal performance. The technique takes only a few minutes, replacing the hours of chemical analysis that were once needed to evaluate ground samples of fodder. Once screened, selected varieties could be tested further to verify their performance potential.

The greater nutritional quality of legume residues allows them to be used as a supplement to livestock diets based on cereal stovers and other low-quality forages. Optimizing the amount of cowpea haulms in livestock diets was one focus of a research project sponsored by the CGIAR Systemwide Livestock Program on the use of cowpea fodder. As smallholder livestock systems evolve and become more market-oriented, the type of diets fed to livestock often changes. Legume fodders remain an important part of these changing diets. The development of cowpea varieties that feed both people and their farm animals better will give farmers new and wider choices.

There is still much to be done. With significant variation existing within cowpea germplasm collections, we can continue to improve dual-purpose varieties. Modern technologies are available to allow the rapid screening of important quality traits. Techniques such as NIRS for quality analysis and marker-assisted selection for desirable traits promise to speed the future development of new varieties of dual-purpose cowpea.

To conserve or not to conserve?

IITA maintains more than 15,000 accessions of cowpea in its genebank. Photo by IITA.
IITA maintains more than 15,000 accessions of cowpea in its genebank. Photo by IITA.

Crop improvement through breeding and biotechnology is one way of tackling the challenges of feeding the world. Conservation of genetic resources is an important component of crop improvement, providing a pool of materials for the researchers to draw from.

IITA’s Genetic Resources Center (GRC) created in 1975, maintains over 28,000 accessions of six main staple crop collections that are available to food and agriculture researchers worldwide working on crop improvement. They are cowpea or “black-eyed pea” (Vigna unguiculata L.), maize (Zea mays L.), soybean (Glycine max (L.) Merr.), cassava (Manihot esculenta Crantz), yam (Dioscorea spp.), and banana (Musa spp.).

Over 50% of the collection is made of cowpea collected from 89 countries, mainly in Africa, and other Vigna spp. It is also the most shared, with 54 of all the germplasm materials being distributed.

Ex situ conservation in IITA genebank: medium-term storage, 5 °C. Photo by IITA.
Ex situ conservation in IITA genebank: medium-term storage, 5 °C. Photo by IITA.

Since 1985, IITA has distributed germplasm of cowpea and its wild Vigna relatives for genetic improvement research to institutions in sub-Saharan Africa, Asia, USA, and South America. This has contributed to the development of new cultivars or varieties currently adopted by rural farmers in the regions.

The effectiveness of the distribution system from the genebank, the use of the distributed germplasm, and conservation costs were assessed in a study conducted by Victor Manyong, Dominique Dumet, and A.T. Ogundapo from IITA and D. Horna from the International Food Policy Research Institute. Likewise, the impact of the conservation of germplasm of cowpea and wild relatives was examined to justify the conservation efforts.

Questionnaires were e-mailed to partners who had collected germplasm from GRC between 1975 and 2009 to determine the ease of accessing material and their use. To estimate the cost of conserving a unit of the two crops, the Decision Support Tool (DST) developed by IFPRI was used.

Ex situ conservation in IITA genebank: medium-term storage, in vitro. Photo by IITA.
Ex situ conservation in IITA genebank: medium-term storage, in vitro. Photo by IITA.

Only about 13% of the beneficiaries responded but they accounted for about 84% of the accessions distributed to beneficiaries in West Africa, Asia, East Africa, Europe, and North America.

No responses were received from beneficiaries in Australia, the Caribbean, Central Africa, the Middle East, North Africa, South Africa, and South America. This may partly have been due to lack of updated contact details in the genebank’s electronic database. This needs to be improved for future feedback surveys.

Use of cowpea and wild Vigna germplasm
The study findings show that most of the distributed cowpea and wild Vigna accessions were used for breeding followed by activities in agronomy and biotechnology research. However, in many cases, they had multiple uses, such as breeding, biotechnology, and agronomy.

Between 2001 and 2005, about 76% of the accessions were used for various agricultural research activities and were found adaptable to different agroecological zones, from forest to the savanna in the tropics and subtropics. Derived, Sudan, and Sahel savannas were recognized as the adaptable agroecological zones for the cultivation of cowpea and wild Vigna.

Ex situ conservation in IITA genebank: long-term storage, −196 °C. Photo by IITA.
Ex situ conservation in IITA genebank: long-term storage, −196 °C. Photo by IITA.

The majority of the users of the germplasm found it easy (32%) to very easy (68%) to get the material from the genebank. Only a few experienced difficulties. These included the inability of the genebank to supply the required quantities (3% of accessions), poor collaboration with NARS and universities (3%), long bureaucratic procedures to acquire germplasm (2%), and improper documentation of the passport database of accessions (1%).

Desired traits
High yield and pest resistance were the two traits desired by the majority of agricultural researchers who made requests, irrespective of their specialization. Other desired traits included compatibility to cross with other accessions, seed color and size, nutritive value, palatability and attractiveness, drought tolerance, nematode resistance, early flowering, and storability.

Moreover, many were satisfied with the accessions they received. Findings show that 68% of the accessions received by agronomists met their desired traits, 76% for food technologists, but only 3% for breeders where the main issue was the low level of resistance to pests and diseases. However, the breeders recorded 100% satisfaction in the exploitation of accessions for seed color, seed size (good), and compatibility with crossing. Likewise, 95% satisfaction was achieved on high seed yield and 74% on the combination of high yield and pest resistance by some of the breeders.

Cost of conservation
The structure cost of the genebank in the DST has four categories: capital, quasi-fixed, variable labor input, and variable nonlabor input. Capital inputs include infrastructure, such as germplasm storage and genebank facilities, and equipment for field operations and offices.

Ex situ conservation: field genebank, IITA. Photo by IITA.
Ex situ conservation: field genebank, IITA. Photo by IITA.

Using 2008 as a reference year, US$358,143 and $28,217 was spent annually on the conservation and management of cowpea and wild Vigna. The capital cost took the major share of the costs, followed by quasi-fixed costs for scientific staff, nontechnical labor, and nonlabor supplies and consumables. Each accession cost about $72 for cowpea and only about half of that for wild Vigna. A large share of the expenditure, $28,537, went into the regeneration of 2,228 accessions of cowpea, at an average cost of approximately $12.81 per accession.

Cowpea germplasm is regenerated in the screenhouse to produce high quality germplasm, with considerations of purity and sanitation, hence the relatively high cost per accession. Seed health testing ($13.94/accession) and distribution ($22.63/accession) were the other high costs.

One way to reduce these costs is by increasing the number of accessions, thus lowering the unit cost. Also, upgrading and expanding the current infrastructure to improve the efficiency of the genebank were recommended.

Using molecular tools to develop Striga-resistant cowpea

Striga-infested field. Photo by IITA.
Striga-infested field. Photo by IITA.

Witchweed, Striga gesnerioides (Willd.), continues to be a major menace to production in West and Central Africa, where cowpea is an important crop.

This parasitic weed feeds on cowpea plants, leading to severe chlorosis or yellowing, wilting, stunting, and even the death of susceptible hosts. Annual yield losses are estimated in millions of tons.

Collaborative project
A collaborative project funded by the Generation Challenge Program has taken a close look at the Striga problem and is using molecular tools to identify new sources of resistance. Marker-assisted selection or breeding (MAS or MAB) is being used to facilitate the selection of lines with resistance to Striga. In 2008 and 2009, the Institut National de l’Environnement et des Recherches Agricoles (INERA) of Burkina Faso and IITA undertook a study to identify potential sources of Striga resistance, worked with farmers to articulate their problems and preferences, and tested new Striga-resistant improved lines developed using MAS.

Prior to the breeding activity, participatory rural appraisal (PRA) and farmers’ participatory variety selection (FPVS) sessions were organized in seven Striga hot-spots in Niger and Burkina Faso, which are major cowpea-producing areas. During the 2 years, in Niger, 403 farmers contributed to the FPVS and several of their preferred cowpea lines were selected.

To determine farmers’ preferences in Niger, germplasm of 24 cowpea varieties with various characteristics (seed color, seed size, plant type, maturity, and Striga resistance) were planted in farmers’ fields and used for the PRA and FPVS. The same 24 accessions were also planted in two fields at IITA’s Minjibir Experimental Farm as checks.

Trial sites for 2009 FPVS activities in NIger and Nigeria
Trial sites for 2009 FPVS activities in NIger and Nigeria

In Niger, researchers and local agricultural agencies worked with farmers in their fields. Based on interviews and responses to questionnaires, farmers acknowledged that Striga is a serious problem that seems to be increasing, said IITA scientists Satoru Muranaka and Ousmane Boukar, and Jean Baptiste Tignegre of INERA, who collaborated on the project. Farmers, they added, also suggested that the use of resistant varieties could be a solution. This reconfirmed the importance of Striga resistance as a breeding goal.

The project has also confirmed farmers’ preference for IT00K-1148 and IT90K-372-2-1 because of their agronomic traits. These lines are susceptible to the dominant race of Striga in Niger. In the FPVS, farmers preferred new lines, such as KVX30-309-6G and TN256-87, which also lacked resistance to Striga.

Of the top five genotypes selected by the farmers in the seven locations, only two—IT99K-573-2-1 and IT98K-205-8—were picked by farmers because these met their preferences for Striga resistance, early maturity, and high yield potential.

Farmers preferred the white-seeded variety for consumption but genotypes with brown seed color that are early maturing and high yielding were also acceptable. The surveys and FPVS activities showed that farmers use consistent selection criteria based on various traits.

Because of unstable rainfall and other problems in 2009, farmers did not get good grain yields, although in a few cases, Striga-resistant IT99K-573-2-1 showed 4−6 times more grain yield (average 214 kg/ha compared with 37−51 kg/ha for local varieties).

Both IT99K-573-2-1 and IT98K-205-8 showed resistance to Striga in all the locations used for the trial. These varieties could be recommended for cowpea production in Southeastern Niger where Striga and drought are major constraints, and for use as sources of resistance genes in breeding other varieties.

Marker-assisted breeding
Using MAB, pot and field experiments in 2008 and 2009 evaluated backcrossed varieties (crossed to their parents) for various traits, such as resistance to Striga, flowering and maturing dates, disease resistance (to bacterial blight, virus, and leaf rust), and seed characteristics.

Farmers selecting cowpea varieties in Niger. Photo by IITA.
Farmers selecting cowpea varieties in Niger. Photo by IITA.

Of the 60 genotypes tested in a pot screening trial in the Maradi station of the Institut National de Recherche Agronomique du Niger (INRAN) from October 2008 to November 2009, 18 showed Striga resistance. Results confirmed that the Striga race (SG3) dominant in two locations in northern Nigeria is also dominant in the four trial locations in southeastern Niger. Field trials had been conducted earlier in Kano and Borno States in Nigeria. Hence, the same Striga-resistant genetic resources could be used for breeding varieties for these areas.

Two existing sequence characterized amplified region (SCAR) markers, 61R and MahSE2, were earlier identified to have the potential for use in MAB for SG3 Striga resistance. To confirm this, pot experiments were conducted using Striga-resistant lines that had been developed using MAS. Results showed a higher percentage of resistant plants in the MAB-developed populations than in the control (those that did not use MAB). SCAR marker MahSE2 showed 88% and 96% marker efficiency for evaluating Striga resistance in backcrossed populations.

Pyramiding or building up Striga resistance in these breeding lines via MAB is important. However, further exploration of appropriate markers is needed to develop efficiently the varieties preferred by farmers. Likewise, more markers linked to various traits that meet farmers’ preferences identified in the PRA and FPVS also need to be converted to SCARs for use in MAB.

This project was able to identify germplasm lines with resistance to Striga races predominant in the Niger Republic; identify farmers’ constraints and preferences to aid in selecting for important traits to combine with Striga resistance; and conduct with farmers the participatory field testing of the new Striga-resistant improved lines developed via the MAB method. It also confirmed the efficiency and effectiveness of MAB for Striga resistance