For too long, a versatile crop, capable of providing huge benefits for health and wealth stayed on the sidelines, largely below its economic potential and comparatively neglected by research. More recently, however, interest in this grain legume has greatly increased and its benefits have been more widely appreciated and publicized.
Cowpea, or black-eyed pea, is one of the few crops that could positively influence the nutritional status in sub-Saharan Africa. Grown by farmers mostly in West Africa, it is increasingly gaining prominence in the fight against hunger and poverty.
This is reflected in its dual roles as a source of protein for humans that is cheaper than animal products and a way to raise the quality of livestock through improving their feed. Cowpea also provides higher returns on investment than other crops grown in the region where it thrives best.
Unfortunately, support for cowpea research has been relatively low, unlike that for other crops such as wheat and potatoes. Consequently, this has limited the improvement of cowpea.
The situation is not being helped by the negative impact of climate change and unfavorable abiotic factors in the regions where the crop is mostly grown.
Over the years, IITA and its international and local partners have developed solutions to tackle the constraints faced by this â€œwonderâ€ crop.
These include the development and deployment of improved, Striga-resistant, drought-tolerant, and early maturing varieties. More recently, work is ongoing to produce varieties resistant to the damaging legume pod-borer (Maruca).
The impact of these varieties on rural livelihoods and poverty is slowly but surely being felt.
Advances in science could help to further raise cowpea yield. With more resources now going into cowpea research and farmers’ participation in variety selection, even better performing varieties should be available soon.
These efforts have already produced positive results in the target regions but only on a relatively small scale when set in the context of all sub-Saharan Africa.
The task before stakeholders is to join hands with IITA now to advance this crop and to save Africa. The time to act is now.
The germplasm collections in genebanks are an invaluable resource for the future. The conservation of this biodiversity is tied to agricultural production and represents a safety net for the food security of future generations.
In addition to the conservation, multiplication, regeneration, and characterization of these collections, another central function of a genebank is the expansion of germplasm collections to cover as much agrobiodiversity as possible.
IITA works on cowpea improvement and holds the largest cowpea germplasm collection in the world (15,115 accessions); 10,814 (71.5%) of these were collected in Africa or acquired from African national programs.
High protein food legume
The cowpea is a very important, widely adapted, and versatile grain legume of high nutritional value. It is mainly produced and consumed in Africa where it provides a major low-cost dietary protein for millions of smallholder farmers and consumers who cannot afford high protein foods, such as fish and meat. Food legumes, particularly cowpea, have high protein contents. Cowpea contains 24% protein, 62% soluble carbohydrates, and small amounts of other nutrients.
It is a very low-input crop, traditionally grown in intercropping systems. Cowpea contributes to soil fertility through nitrogen fixation and is also cultivated to prevent soil erosion.
The worldwide area cultivated with cowpea in 2008 was estimated to be 11.8 million ha with an annual production of 5.4 million t of dried grains (FAOSTAT 2010).
At IITA, cowpea is maintained in two storage conditions, medium (5Â°C) and long-term (-20Â°C) at an optimal water content of 7âˆ’8% fresh weight basis. The viability of most accessions stored at â€“20Â°C for 25 years remains as high as 90%.
To avoid losses of genetic diversity and to guide future sampling, researcher Anne Rysavy of the University of Hohenheim (now with the University of Tuebingen), GIS Specialist Kai Sonder (now with CIMMYT), and the head of IITAâ€™s Genetic Resources Center, Dominique Dumet, assessed the geographic coverage of the current collection to get an overview of the cropâ€™s conservation status. The study identified areas in Africa where the probability of finding more and diverse Vigna unguiculata accessions is highest and where further collection should be done.
Gap analysis is an evaluation technique applied to provide wide geographic information on the status of different species and their habitats using satellite data and different computer tools and by digital map overlays in a geographic information system (GIS). Gaps refer to geographical areas that are underrepresented in the collection and where cowpea is expected to occur based on agrometeorological and other factors.
GIS can be a powerful tool for analyzing spatial distribution of a species. Combined with biophysical information from germplasm collections, it can help in conducting surveys and prioritizing future sampling areas. Areas that have not yet been sampled can be targeted for collecting missions so that the material can be conserved ex situ or using in situ conservation strategies.
Specifically, the study analyzed, corrected, and georeferenced the available passport data for cowpea. It also applied different GIS tools to identify gaps in previous collection areas, and predicted areas where new diversity is likely to be collected and/or areas where diversity erosion risk is highest, e.g., from climate change, civil war, deforestation, etc.
This study used spatial analysis tools and software applications, such as FloraMapTM, HomologueTM, ArcGISTM, and DIVA-GIS, including the predictive models EcoCrop, BIOCLIM, and DOMAIN to perform the gap analysis on the existing cowpea germplasm collection at IITA and identify potential areas for future conservation activities.
First the country coverage of georeferenced cowpea accessions was determined. Then, ecogeographical site descriptors (temperature, precipitation, length of growing period, and altitude) were extracted to determine areas with environmental conditions favorable to cowpea. Based on this, regions with similar environmental conditions were identified using GIS techniques.
Gaps in cowpea collection
Study results provide an overview of the actual distribution, agroclimatic preferences, and potential distribution of cowpea.
The geographical scope of the study focused on sub-Saharan Africa. Results indicated that cowpea can be found approximately between 15Â°N and 20Â°S, and over a large range of climatesâ€”temperature as well as precipitation. However, it occurs most likely in subtropical to tropical conditions characterized by warm temperatures (annual average >20Â°C) and relatively high annual precipitation (>250 mm).
The distribution of the total number of cowpea accessions held in the IITA genebank is very diverse with a certain concentration in West Africa (see map). Nigeria and Niger account for nearly 50% of all accessions. The origins of the remaining 50% are unequally distributed across the continent. Several countries such as Burundi, Equatorial-Guinea, Eritrea, Guinea-Bissau, Namibia, and Rwanda are not represented.
Depending on the country, the total number of accessions collected within Africa ranged between one (Algeria and Angola) and 3,813 (Nigeria). Nigeria ranked first with 35.3% and Niger second with 11.6% (1,249 accessions).
All the methodologies used identified areas where, according to agroecological similarities, the probability is high of finding more cowpea accessions and no collections have been carried out yet, or very few accessions have been collected. They proved to be useful approaches to conserving the genetic diversity of crop species.
Based on the predictive models, the following countries were identified as the priority for the acquisition of new germplasm: Angola, Burundi, Guinea-Bissau, Eritrea, Equatorial-Guinea, Namibia and Rwanda, especially since no collections have yet been made in these countries. In addition, further sampling is recommended in countries with small numbers of georeferenced accessions, such as Botswana, Congo, DRC, Gambia, Lesotho, Liberia, Madagascar, Sierra Leone, Sudan, Swaziland, and Uganda.
Germplasm acquisition will be done through the duplication of existing national collections at IITA with the support of the Global Crop Diversity Trust (GCDT), and specific collecting missions to capture missing diversity. The GCDT has commissioned IITA to lead the development of a global conservation strategy for the genetic resources of cowpea and its wild relatives with an emphasis on Africa.
The cowpea is one of the most important grain legumes in Africa. Cowpea is both economically and nutritiously significant. Its ability to fix nitrogen efficiently and grow in a wide range of conditions means that the cowpea is also a suitable companion for a wide range of other food and fiber crops.
Nigeria is the worldâ€™s largest producer of the crop, growing 45% of the global yield. However, this total amount has dropped considerably in the past 30 years, from 61% in 1981 to 45% in 2004. With cowpea playing such a key role in the agriculture and food supply of Nigeria, production and processing practices need to be improved, emphasized Thierno Diallo of IITAâ€™s Postharvest Utilization Unit.
The production and processing begins before the seeds have even been planted. Land clearance involves cutting down trees, pulling up stumps, leveling the land, and extracting roots and stones.
Of all the agricultural operations, land clearance is the most difficult and costly. After this the soil must be properly prepared to create good conditions for the seeds to germinate and grow. This starts with the time- and energy-consuming preparation of the seed bed and includes planting and fertilizing. The plant must then be maintained for its life span. This means preventing weeds, pests, and organisms that cause diseases such as bacteria, fungi, and viruses, from severely affecting the crop, as well as keeping the cowpea irrigated if so required.
When fully mature the plants are ready to be harvested. This involves cutting the dry pods before they are attacked by birds or rodents. After this the pods must be opened to release the grains. This is done in two stages: first, the pods are beaten to open them and then they are scooped up and fanned out to separate the grains from the shells in a process called threshing. The grains are collected and dried to increase quality and shelf life, then stored.
All of these operations are traditionally done by hand or with the help of animals and are thus associated with drudgery. â€œThe mechanization of existing tools and the promotion of efficient farm management techniques could be the way to increase Nigerian cowpea production once again,â€ Diallo said. Diallo had been involved in designing some processing machines now in use by small industries in Nigeria and other sub-Saharan African countries.
The advantages of mechanization have already been demonstrated with threshing. Traditionally, sticks were used to beat the grains out of the pods but they sometimes broke the seeds, rendering them useless. In the 1990s, IITA introduced a tool called the Fail-safe Flail, which prevented most of the damage to seeds. The motorized multicrop thresher further improved the process as it could do the job of several workers with flails, taking away much of the drudgery. These two devices increased the productivity of threshing. The recent introduction of a fanning system to the multicrop thresher has made it significantly better still.
Drying is another area where successful mechanization has been implemented. Farmers used to spread the cowpea grains on the ground to dry under the sun. The introduction of drying platforms has not only made the process more hygienic but also more flexible as it does not depend on the sun any longer. Dryers of various designs and capacities are available, from small drying shelves to medium-capacity cabinet dryers and high-capacity rotary dryers. The larger dryers use fuels such as charcoal, wood, or diesel as the source of heat. Some are equipped with a milling facility to produce flour.
By upgrading to machines such as these a farmer could not only get through the various stages of production faster but also run systems such as irrigation, uninterrupted. This in turn would cut costs and improve overall yields as well as boosting confidence and encouraging more people to grow cowpea.
Furthermore, the high cost of purchasing or renting a machine would be offset by the fact that one machine is now capable of completing many different tasks.
Thus, when it comes to producing and processing cowpea, a move to mechanization is essential to fulfill the demand for the crop in Africa and worldwide, according to Diallo.
IITA and partners in the Netherlands and the United States are developing genomic tools that will facilitate the development of improved cowpea varieties with traits such as drought tolerance.
An IITA-Lukas Brader Postgraduate Fellow, Eugene Agbicodo, who carried out the genetic analysis of drought tolerance in cowpea and subsequently constructed a linkage map of the crop, identified portions on the cowpea genome where genes that have effects on drought tolerance and resistance to bacterial blight could be located.
His findings, a landmark in marker-assisted selection in cowpea improvement, will help shorten the plant breeding process.
Similar work has been reported by researchers at the University of California, Riverside, and researchers at the two institutions are comparing notes on the outcomes of their research to see areas of agreement and possible collaboration, according to Christian Fatokun, Cowpea Breeder, who supervised Agbicodo’s genomic mapping work at IITA.
â€œIf both parties are able to find areas of agreement or concurrence, such areas of the genome would be of immense benefit when marker-assisted selection is applied in cowpea breeding. So what will normally take about 10 years to accomplish could be done in three years or even less,â€ he said.
With about 70% of world cowpea grown in the savanna region of Africa, the protein-rich legume provides not only incomes but also improves the health of its consumers. However, cowpea faces several production constraints, among which are diseases, insect pests, parasitic weeds such as Striga, and drought which is becoming increasingly important in the cowpea-producing zones of sub-Saharan Africa.
Agbicodo phenotyped and genotyped a set of cowpea recombinant inbred lines generated at IITA in Ibadan. Phenotyping was carried out in Ibadan and Kano, Nigeria, while the genotyping was carried out at the University of Wageningen, The Netherlands.
Consequently, he constructed a cowpea genetic linkage map using the data obtained from genotyping and phenotyping. The linkage map showed molecular markers that defined quantitative trait loci (QTLs) with effects on drought tolerance and resistance to bacterial blight among others.
A new collaborative project has been launched to develop novel approaches against an old problem affecting cultivated legumesâ€”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.
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.
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.
Nigeria has released two new cowpea varieties to raise production and improve farmersâ€™ incomes.
The varietiesâ€”IT89KD-288 and IT89KD-391â€”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 Nigeriaâ€™s strain of Striga gesnerioides (a parasitic weed that severely lowers yield).
â€œIt also has a yield advantage of at least 80% over the local varieties,â€ 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.
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.
â€œIT89KD-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,â€ said Hakeem Ajeigbe, IITA Extension/Dissemination Specialist.
â€œThe 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,â€ 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).
â€œThe demand for these improved varieties is high because of their superior yields and their acceptability by consumers,â€ Kamara said.
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 decadesâ€”a quiet revolution that is greater in magnitude compared to that of cereals and all other pulses.
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.
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 â€˜lobiaâ€™ in India, â€˜kundeâ€™ in east Africa, â€˜beansâ€™ and â€˜wakeâ€™ in Nigeria, â€˜niebeâ€™ in francophone Africa, â€˜southern peaâ€™ and â€˜blackeye peaâ€™ in the USA, â€˜feijÃ£o caupeâ€™, 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 IITAâ€™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 75â€“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 â€˜Big Buffâ€™ (IT82E-18) in Australia; â€˜Biraâ€™ (TVx 3236) in Angola; â€˜Titanâ€™ (IT84D-449) and â€˜Cubinataâ€™ (IT84D-666) in Cuba; â€˜Asontemâ€™ (IT82E-16), â€˜Ayiyiâ€™ (IT83S-728-13), and â€˜Bengplaâ€™ (IT83S-818) in Ghana, â€˜Akashâ€™ (IT82D-752) (sky) and â€˜Prakashâ€™ (IT82D-889) (light) in Nepal; â€˜Sosokoyoâ€™ (IT84S-2049) in Gambia; â€˜Pkoko Togboiâ€™ (IT85F-867-5) in Guinea Conakry; â€˜Korobalenâ€™ (IT89KD-374) and â€˜Sangarakaâ€™ (IT89KD-245) in Mali; â€˜Dan IITAâ€™ (TVx 3236) (son of IITA) and â€˜Dan Bunkureâ€™ (IT89KD-288), IT90K-76, IT90K-82-2, IT90K-277-2, and IT93K-452-1, in Nigeria; â€˜Melakhâ€™ and â€˜Mourideâ€™ in Senegal; â€˜Pannar 31â€™ (IT82E-16) in South Africa; â€˜Dahal Elgozâ€™ (IT84S-2163) (gold from the sand) in Sudan; â€˜Umtilaneâ€™ (IT82D-889) in Swaziland; and â€˜Bubebeâ€™ (IT82E-16) in Zambia; â€˜Vamban 1â€™ (IT85F-2020), â€˜Pant Lobia-1â€™ (IT98K-205-8), and â€˜Pant Lobia-2â€™ (IT97K-1042-3) in India; and many more.
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 â€˜wheat-cowpea-riceâ€™ 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.
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.
B.B. Singh, Visiting Professor
Department of Soil and Crop Sciences,
Texas A&M University, College Station, TX 77840, USA
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 â€œsoul foodâ€.
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 worldâ€™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.
Itâ€™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 worldâ€™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?
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 â€œbirthplaceâ€ 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 IITAâ€™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 Africaâ€”the cradle of cowpea diversity.
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.
Aleksandar MikiÄ‡ (firstname.lastname@example.org), Mirjana MiloÅ¡eviÄ‡, Vojislav MihailoviÄ‡, Charassri Nualsri, DuÅ¡an MiloÅ¡eviÄ‡, Mirjana VasiÄ‡, and DuÅ¡ica DeliÄ‡
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, mletaÄki graÅ¡ak (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 â€œCremoneseâ€ 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 â€œDomaÄ‡aâ€, 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 45Â°20′ N, 19Â°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.
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.