Vigna subterranea (common names: Bambara groundnut, Bambara nut, Bambara bean, manicongo, Congo goober, ground-bean, It reproduces via geocarpy, ripening its pods underground, much like the peanut (also called a groundnut).

The plant originated in West Africa. As a food and source of income, the Bambara groundnut is considered to be the third most important leguminous crop in those African countries where it is grown, after peanut and cowpea. The crop is mainly cultivated, sold and processed by women, and is, thus, particularly valuable for female subsistence farmers.

Bambara groundnut represents the third most important grain legume in semi-arid Africa. It is resistant to high temperatures and is suitable for marginal soils where other leguminous crops cannot be grown. It is a low-impact crop. The entire plant is known for soil improvement because of nitrogen fixation.

The pods can be eaten fresh or boiled after drying, and can be ground either fresh or dry to make puddings.

Biology

thumb|The small yellow flower of Bambara groundnut ('Vigna subterranea') emerges at the base of the plant near soil level. The crop is almost entirely self-fertilising, which limits natural genetic diversity.

Bambara groundnut is a herbaceous, intermediate, annual plant, with creeping stems at ground level. It is a small legume plant that grows to a height of with compound leaves of three leaflets having stipules about 3 mm long. The flowers have a tube calyx about 1 mm long and 5 lobes about 1 mm long as well as a whitish yellow corolla, 4–7 mm long. The fruit is an indehiscent pod almost globose about 2.5 cm in diameter. Flowers appear 40–60 days after planting. The seeds will form pods encasing seeds just below the soil. The pods are round, wrinkled and each contains one or two seeds that are round, smooth and very hard when dried.The seeds may be cream colored, brown, red, mottled or black eyed and their size is about 8.5–15 mm × 6.5–10 mm × 5.5–9 mm. It is also cultivated in Mauritius and the Comoro Islands. In Asia, it is cultivated in India, particularly in the state of Karnataka, and in Indonesia, especially on the island of Java. In Australasia, it is grown in Papua New Guinea.

In the Caribbean, it is grown in Dominican Republic where it is known as "manicongo", it was once common in local markets but has since declined in prevalence over the past decades. This particular lineage, descends from seeds that were carried to the Americas by enslaved people during the Atlantic slave trade and the Age of Discovery.

Ecology

thumb|Little plant of Bambara nut/ Bambara groundnut

Biological nitrogen fixation

Like many other legumes, Bambara groundnut fixes atmospheric nitrogen through the process of biological nitrogen fixation. Its potential to be used as an alternative to chemical fertilizer in agriculture has been investigated for many years. The crop can thus be planted on flat terrain, although it is also planted in ridges. Studies show that increased sowing density has a positive effect on production calculated on a per-area basis, but has a negative effect on per-plant yield. It is assumed that at higher sowing densities, increased competition between plants is the cause of lower pod and seed number per plant. For woodland savannas of Côte d'Ivoire, the highest yield is attainable with a plant density of 25 a non-negligible proportion of farmers grow the Bambara groundnut in monoculture and report that its performance is better as a single crop. Moreover, fertilization with phosphorus enhances the crop's nitrogen fixation and increases its nitrogen content.

Harvest and postharvest treatment

The Bambara groundnut typically takes about 130–150 days to mature, but early or late harvests only marginally reduce the yield.

The primary goal of Bambara improvement programs is to focus on seed yield and nutritional quality traits. There is a notable gap between the potential yield of 4 t/ha and the average yield of 0.85 t/ha reported for African countries. Thus, breeding should aim at improving the yield. Results of studies exhibited high protein content among the test genotypes. Similarly, high levels of essential fatty acids, thiamine, ribovin, and vitamin K were recorded. Moreover, scientists examined the chemical properties of starches in Bambara groundnut. The results revealed that seed source and crop management practices affected chemical composition. to 79,155 tonnes

The yield level of Bambara groundnut in Africa varies from 0.6 to 1 tonne per hectare, depending on variety and production conditions. However, unshelled mean yields of up to 3 tonnes per hectare were reported when cultivating some landraces in the transition agro-ecological zone in Nigeria. A low mean yield of 0.85 tonnes per hectare was reported in Ghana under good management practices close to yield levels of other legumes such as cowpeas (0.80 tonnes per hecatare) and pigeon peas (0.78 tonnes per hectare). It is considered to be a neglected and underutilized food source in Benin. The brown hull showed the highest concentrations of rutin and myricetin among flavonoids, while the red hull resulted in having with the highest concentrations of chlorogenic and ellagic acid among tannin compounds.

Macronutrient content

Raw data

Bambara groundnut has nutritive value ranging between 57.9% to 64% carbohydrate and 24.0% to 25.5% protein content. In comparison, soybean (Glycine max) and chickpea (Cicer ariteneum) have 27% and 61% of carbohydrates.

  1. Applications of pressure, heat, infrared radiation, dry extrusion and chemicals such as cysteine have been shown to reduce trypsin inhibitor activity in whole soybean.

Uses

thumb|280x280px|A woman cooks Bambara groundnut over a wood fire in Unyamikumbi village, Singida, Tanzania. Dry Bambara beans can take 3–4 hours to cook, requiring significantly more fuel than other legumes — a factor that limits wider adoption of the crop.

The seeds are used for food, beverages because of their high protein content This presents an obstacle to a more widespread use of this crop. Moreover, if the bean is not cooked enough, it can cause bloating of the stomach, constipation and flatulence.

Use as livestock feed

The Bambara groundnut plays an important role in the diet and culture of populations. The leaves, rich in phosphorus, are used for livestock feed. Seeds are given to pigs and poultry.

Resistance to Abiotic Stresses

Drought Resistance

For the past twenty years [when], a lot of research has looked into how Bambara groundnut plants can survive in dry conditions, mostly by looking at traits that are visible above ground

. The species maintains turgor via osmotic adjustment, reductions in leaf area index, and efficient stomatal regulation to minimize water loss .

Studies on different genotypes have revealed a range of adaptive drought-evasion strategies. For instance, the Botswana genotype DipC1 and the Tanzanian genotype DodR showed comparatively small reductions in seasonal light interception under water stress (37–47%), whereas the Sierra Leone genotype LunT exhibited a much stronger decline of 71%.

Later research showed distinct water-use strategies among landraces: Uniswa Red (from Swaziland) was described as a “water-saver” with early stomatal closure, while S19-3 (from Namibia) was characterized as a “water-spender” with late stomatal closure. These findings were corroborated by subsequent physiological and genetic studies

.

Genetic mapping efforts have also identified quantitative trait loci (QTLs) associated with drought-related phenotypes in crosses between DipC1 (Botswana) and Tiga Nicuru (Mali). Further research by Kundy (2019) demonstrated that Bambara groundnut landraces and the commercial peanut variety “Manje” exhibited similar yield declines under drought stress (59% vs. 55%, respectively), indicating the high potential of Bambara groundnut for drought tolerance breeding.

More recently, root phenomics has become a focus of drought adaptation research in Bambara groundnut. Studies revealed contrasting root system architectures, with deep-cheap rooting patterns in landraces from dry regions and shallow-costly rooting in genotypes from high-rainfall areas. In drought conditions, genotypes with higher root length density at deeper soil layers, such as DodR, showed superior water-foraging ability. These findings suggest long-term ecotypic and possibly genetic differentiation driven by local agroecological conditions.

Heat Resistance

Although Bambara groundnut is generally drought tolerant, high temperatures particularly above 38 °C combined with low relative humidity can reduce pod yield even under irrigation.Genotypes derived from landraces, such as Rarkins (from Burkina Faso), exhibit superior tolerance to simultaneous heat and drought stress compared to others like Black Eye, NAV 4, NAV Red, and Tom. Field studies have demonstrated that average maximum temperatures up to 34 °C did not significantly impair the physiological performance of some genotypes. However, at 33 °C, Uniswa Red exhibited lower pod yields (35.5 g m⁻²) compared to S19-3 (56.6 g m⁻²), while both performed best at 23 °C (151 g m⁻² and 162 g m⁻², respectively).

Subsequent research employing cell membrane thermostability as a metric for heat resistance demonstrated significant variability among genotypes across varying temperatures and exposure durations. The lethal heating duration at 50 °C was suggested as a viable criterion for evaluating genotypes for heat tolerance. These findings demonstrate significant genetic variability in the thermal response of Bambara groundnut, highlighting the necessity of utilizing this diversity in breeding programs aimed at high-temperature environments.

References

  • Bambara Groundnut -- Voandzeia subterranea (L.) Thouars
  • Bambara Groundnut ... a Link from the Past and Resource for the Future
  • Bambara groundnut - NUS Community, Bioversity International