Bambara Groundnut (Vigna subterranea)

Iowa State University, Ames, Iowa 50011

Corresponding author: aamahama@iastate.edu

OUTLINE

1. Overview
2. Etymology
3. Origin, domestication, and geographic distribution
4. Description
5. Growth conditions
6. Production and use
7. Breeding and improvement
8. Untapped potential
9. References
10. Chapter information

1. OVERVIEW

Bambara groundnut (BGN) or Bambara beans (Vigna subterranea (L.) Verdc.) is considered the third most important food legume crop in continental Africa after groundnut (Arachis hypogea) and cowpeas (Vigna unguiculata). It is recognized for its high nutritional value and as a complete crop (15–25% protein, 49–63.5% carbohydrate, 5.2–6.4% fiber, 4.5–7.4% fat, 3.2–4.4% ash, and 2% mineral) (Bamshaiye et al., 2011; Holm & Marloth, 1940; Jideani & Diedericks, 2014; Murevanhema & Jideani, 2013), as well as its tolerance to poor soils, drought, and salt stress, and its ability to produce in conditions where groundnuts/peanuts completely fail. These are possibly the main reasons for it still being maintained and grown by local populations (Adzawla et al., 2016a,b; Olayide et al., 2018). It has recently been declared one of the “crops of the new millennium” (Ahmad, 2012).

2. Etymology

Bambara groundnut is an annual legume belonging to the family Leguminosae (Fabaceae), subfamily Papilionoideae (Faboidea), and the genus Vigna. It had a botanical name change from Voandzeia subterranea (L.) Thouars to Vigna subterranea (L.) Verdc., following a report by Verdcourt (1980). The Bambara groundnut originates from the continent of Africa and is generally cultivated in sub-Saharan Africa. The name Bambara originated from the Bambara district on the upper Niger (Hillocks et al, 2012). It goes by many different names in sub-Saharan Africa (SSA) according to the country where it is grown and even the tribe growing it. Some common names include Congo groundnut, Congo goober, Madagascar groundnut, earth pea, baffin pea, njugo bean (South Africa), voandzou (Togo), Nzama Jugo bean (Malawi), indhlubu (Zimbabwe), nyimo beans, or ditloo in Southern Africa, and underground bean. In Brazil, it is called mandubi d’Angol. Bambara groundnut has long been referred to as a “poor man’s” crop and most commonly as a “women’s” crop because it was grown and tendered mainly by women to achieve food security for the family (Ntundu et al, 2006).

3. ORIGIN, DOMESTICATION, AND GEOGRAPHIC DISTRIBUTION

Studies suggest that Bambara groundnut originated from the continent of Africa (Hepper, 1970), specifically from Timbuktu areas in central Mali, West Africa (Hillocks et al., 2012). However, the primary center of genetic diversity of Bambara groundnut is the northeastern region of Nigeria and northern Cameroon (Dalziel, 1937; Hepper, 1963) from where it spread across sub-Saharan Africa. A secondary center of diversity exists outside Africa and includes Sri Lanka, Malaysia, the Philippines, and India (Rungnoi et al., 2012). It is cultivated extensively by small-scale farmers in the drier regions of sub-Saharan Africa under the traditionally low-input and marginal agricultural production systems (Pasipanodya et al., 2022). The crop currently is widely distributed and grown in tropical regions of America, northern Australia, and Asia (including India, Indonesia, Malaysia, Philippines, and Thailand) but the level of its cultivation is very low. While seldom grown in the United States, Bambara groundnut produces a nutritious food under cultivation throughout Africa. It was carried to America by slaves but has never become as popular as the peanut, which has a higher level of protein and is more robust in growth.

4. DESCRIPTION

The annual leguminous crop is predominantly self-fertilized with cleistogamous pale-yellow flowers and is grown for its underground seeds. The entire plant and growth habit is like those of the common peanut with both erect forms and the low, flat (or open) forms with compound leaves of three leaflets. Like the peanut, it forms pods and seeds on or mostly just below the soil surface, hence the suffix ‘groundnut’ in the name. To set pods underground, the flower stalk elongates and penetrates the soil as the bulbous tip creates a tunnel through which the fertilized flower, attached just behind the tip, is drawn into the soil. There are numerous nitrogen-fixing nodules on the roots. The pods are round, wrinkled, and over half an inch long. Commonly, each pod contains one or two seeds that vary in morphology and color (smooth, round, oval, and in-between, cream, brown, red, orange, mottled, and black) and are very hard when dried.

5. GROWTH CONDITIONS

Bambara groundnut grows best in climates suitable for peanuts, which include bright sunshine, elevated temperatures, at least 4 months free of frost (where applicable), and frequent rains. The plant, however, is highly adaptable with much greater tolerance to harsh conditions than most crops. It yields under conditions too dry for peanuts, such as in the Bambara District near Timbuktu on the Sahara Desert’s Southern fringe. It also is known to grow in rainforest areas and the cool, moist highlands of Zimbabwe. When grown like the peanut, Bambara groundnuts mature between 3 to 6 months from planting depending on climatic conditions and the cultivar.

6. PRODUCTION AND USE

In the past 20 years there has been a slow but steady increase in Bambara groundnut production (FAOSTAT, 2023). Average dry BGN bean production data (1990 to 2021) show that Burkina Faso leads the top ten producers with around 40,000 tonnes (FAOSTAT, 2023).

The seeds may be eaten raw when immature but become too hard when mature, therefore seeds are commonly boiled, roasted, or fried before eating. When roasted or boiled, even the mature seeds are sweet and pleasant tasting. The seeds are often roasted and ground into nutritious flour steamed or fried in oil. Seeds contain 14-24% protein and about 60% carbohydrates (FAOSTAT, 2023). The protein is reported to be higher in the essential amino acid methionine than other grain legumes. Bambara groundnuts contain 6-12% oil, which is less than half the amount found in peanuts, making them not favored as an oilseed crop. The tops (commonly the leaves and stalks) are rich in nitrogen and phosphorus and therefore are used as livestock feed, fodder, and forage (Mubaiwa et al., 2018).

In Africa, Bambara groundnut is often preferred as a dietary supplement to milk from soybean and cowpea (Bamshaiye et al., 2011). It has other health benefits which include a cure for diarrhea (Atoyebi et al., 2018), prevention of high blood pressure (Lin Tan et al., 2020), treatment of wounds and healing epilepsy (FAO et al., 2020), and controlling morning sickness during pregnancy when chewed and swallowed (Jideani & Diedericks, 2014).

7. BREEDING AND IMPROVEMENT

Bambara groundnut is an annual diploid species (2n = 2x = 22), has a complex reproductive system, and is described as recalcitrant to artificial hybridization (Gerrano et al., 2021). The world collection of BGN germplasm is reported to be a little over 6000 accessions from 25 African countries (Muhammad et al., 2020), with the largest number of accessions (2035) being held by the International Institute of Tropical Agriculture (IITA) (Goli, 1997).

Based on the analysis of seeds, Begemann (1988) reported ecogeographic differentiation present in BGN. Characterization and evaluation techniques such as phenotypic descriptors (IPGRI et al., 2000), biochemical markers (Pasquet et al.,1999), molecular markers including amplified fragment length polymorphism (AFLP) markers (Massawe et al., 2002), random amplified polymorphic DNA (RAPD) (Massawe et al., 2003), simple sequence repeat (SSR) markers (Beena et al., 2012; Molosiwa et al., 2013; Aliyu & Massawe, 2013; Redjeki et al., 2020), DArT markers (Olukolu et al., 2012), and single nucleotide polymorphism (SNP) markers (Redjeki et al., 2020) have been used to assess the available germplasm, and all reached the same conclusion of great genetic diversity present.

Even after it being declared one of the “crops of the new millennium” (Ahmad, 2012), little attention from international organizations has been given to the crop. There are currently no breeding programs targeting the development of improved cultivars from segregating families and therefore, to date, there are no registered or improved cultivars of Bambara groundnut. Farmers still use landraces, developed through several generations of mass selection, since most all improvement attempts are limited to the evaluation for yield and yield-related traits of local collections or introduced germplasm. A very early attempt toward improving BGN was by Doku and Karikari (1971) who reported the development of cultivated Bambara groundnut (Voandzeia subterranea var. subterranea) from wild Bambara (V. subterranea var. spontanea) to change from wild characteristics such as: from open to a compact or bunch growth habit, from outbreeding to inbreeding system to reduce or eliminate dependence on ants for pollination, increased stem number, reduction in leaf area, and reduction in shell thickness.

8. UNTAPPED POTENTIAL

Several review articles have documented the important role BGN will play towards global food security (Hillocks et al., 2012; Gregory et al., 2019; Paliwal et al., 2021; Khan et al., 2021; and many more), yet the crop has not received the attention necessary to make the needed advances in the improvement and release of high-yielding biotic and abiotic stress-tolerant varieties to farmers. Breeding that is focused on solutions to the reasons for the crop being underutilized—including poor processing methods; the hard-to-cook phenomenon (3 to 4 hours) (Mubaiwa, 2018); relatively low yields; lack of mechanization related to planting, harvesting, and different post-harvest operations, such as its drying, de-husking, and hard-to-mill properties—can improve the commercial potential of the crop, which is currently low (Ibny et al., 2019). This will make the crop more attractive for production in areas outside the current growing zone, thus expanding its production area. Various science-based research (Esan et al., 2023, among others) have reported significant differences among lines or accessions evaluated, further confirming the variability present, and therefore the potential for improvements, with research-center yields of 3.0 to 4.5 t/ha reported (Pasquet et al., 1999; Azam-Ali et al., 2001).

Through conventional breeding, the application of biotechnology, and recent “omics” technologies (transcriptomics, proteomics, and metabolomics), significant breakthroughs in various crops have been realized in molecular biology, genetics, and elucidation of the molecular mechanism of complex traits which include stress tolerance, yield, flowering, crop maturity, and nutritional value and have led to increased food production. For the past two decades, the application of SNP technology, among other advances, yielded significant impacts on crop improvement and the description of genetic diversity in major crops. However, due to the lack of attention given to BGN by breeders and both national and international funding organizations (Heller et al., 1997; Massawe et al., 2005; Oyeyinka et al., 2015; Paliwal et al., 2021; Will, 2008; Williams & Haq, 2002), these technologies and their potential application for increased food production will remain untapped in BGN. Given the genome sequencing efforts undertaken in BGN (Salazar-Licea et al., 2022), coupled with the inherent attributes of the crop—high nutritional value, tolerance of abiotic stresses, and its potential resilience to climate change—support for this crop should be a high priority in the near future, if not now.

9. REFERENCES

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10. CHAPTER INFORMATION

Chapter citation: Mahama AA. 2023. Bambara Groundnut (Vigna subterranea). In: Chen K, Byrne P (Eds.) Understudied Indigenous Crops. Fort Collins, Colorado: Colorado State University. Date accessed. Available from https://colostate.pressbooks.pub/understudiedindigenouscrops/chapter/bambara-groundnut/

Chapter editors: Katheryn Chen and Patrick Byrne