Food security has long been a vexing subject that is yet to be resolved. A significant increase in population and a decline in available water and arable land are limiting agricultural viability (1). Furthermore, global climate change is a huge impediment to existing production processes, while some arable land may become inaccessible for agriculture in the future as ice melts. The current global situation is so grave that millions of people are going hungry, and many are dying as a result of malnutrition. Since the green revolution began in the 1960s, greater irrigation and the use of inputs like chemical fertilizers and pesticides have enhanced the productivity of the world’s major staple crops (especially wheat, maize and rice) (2). However, future food security is threatened due to human dependence on less than 1% of edible plant species, as well as the detrimental effects of climate change and resource limitation (2, 3). Having constant, reliable, and low-cost access to a diverse range of healthy foods across a range of dietary preferences is what is meant by the term “food security” (4). Over the last decade, more than 800 million individuals have been reported as chronically undernourished globally, with around 821 million instances recorded in 2017 (5). With rapid population increase and quicker loss of non-renewable natural resources, it has become critical to diversify modern intensive agriculture to suit the diverse human demands. Diversifying agricultural output has several benefits for farmers and the local community, including biodiversity conservation, enhanced soil and plant health, less vulnerability to pests, diseases, and extreme weather events. Therefore, the present sustainable development goals (SDGs) emphasize agricultural diversification through the use of undervalued and forgotten crops.

After cereals, which have been a staple of the rationed human diet for millennia (6–8), legumes have been identified as the second most relevant plant source for human and animal dietetics (9), especially in drought and famine situations (10). In order to satisfy the ever-increasing need for vegetable proteins, there has been a recent shift in focus toward underused legumes as a potential source of blooming new alternative protein sources (11). Reduced malnutrition could help reduce global disease burden by 32%, as estimated by the World Health Organization (WHO): 115 million children under the age of five are stunted; 462 million adults are underweight; 41 million children are overweight and obese; and 1.9 billion adults are overweight and obese (12). Success in introducing such novel legumes to a region has the potential to increase dietary diversity and reduce the prevalence of malnutrition. A country’s agrarian standing may also be bolstered in this way, since it will provide new chances for domestic businesses, raise living standards for locals and decrease the need to rely on foreign suppliers. Many types of legumes, whether they are wild or domesticated, are now only farmed in a tiny fraction of their original range. Orphan legumes/underutilized plants like these have the potential to contribute to sustainable agriculture. Thanks to the fact that they can be bred for desirable traits like increased nutrition and resistance to stresses (13). Very little is known about the lesser utilized crops, and knowledge regarding these is limited to areas with special cultural or historical significance. Although they have become increasingly main-stream, they have received less international attention (14). The family of legumes, often known as Fabaceae or Leguminaceae, is the third largest in the world in terms of total population. The legumes are reported to be cultivated in broad variety of environments, from deserts to woodlands, alpine to aquatic and from the African rainforests to the Amazon. It is believed that they originated in Africa, made their way to South America and then spread north to North America and ultimately the rest of the world. Large populations of these may be found all throughout the South Asian continent and the Indo-Pacific. Caesalpinioideae, Mimosoideae and Papilionoideae are the three subfamilies based on floral characteristics, which make up this large family. The Papilionoideae, with 476 genera and over 14,000 species (15), is the most numerous, followed by the Mimosoideae with 77 genera and roughly 3,000 species and the Caesalpinioideae with 162 genera and roughly 3,000 species. However, only a small number of legumes including peas, soybeans and a few types of beans are widely consumed. There are still about 700 genera and 20,000 species that can be developed and incorporated into the mainstream for domestication and human consumption.

Increased visibility of underutilized legumes’ stems from the fact that, they can better endure to a range of climatic conditions (5). Since legumes are one of the most numerous plant families and contain a lot of proteins, we have many possibilities to pick from. It is unfortunate because legumes are an excellent substitute for those trying to eliminate or reduce their intake of animal products. Cowpeas, pigeon peas, and Bambara groundnuts are underrated legumes that can add a lot of nutritional value to our diets. Such legumes are widely produced in areas where they have traditionally functioned as a staple crop, but are consumed by significantly fewer people in other parts of the world. In addition to supporting the small farmers who grow them, eating more of these legumes will increase your intake of protein and other essential nutrients. Additionally, underutilized legumes can aid in the worldwide fight against hunger and malnutrition. People in these areas considerably benefit from these crops because of their resilience and hardiness, which are especially important given the scarcity of other food sources. Their increased resistance to climate change, pests, and diseases makes them a potentially game-changing crop for the second green revolution in farming. There are multiple ways in which the widespread adoption of underutilized legumes can contribute to the advent of a second green revolution. Underutilized legumes are a highly nourishing and sustainable food supply that can aid in increasing food security and decreasing poverty in many regions of the world. Further, these crops are a versatile and robust, that may be grown in a wide variety of agroecological and production systems and can improve soil health and increase food production. Further, increasing the use of underutilized legumes can boost economic growth and alleviate poverty in many regions of the world. The local economy can be stimulated and new jobs created by expanding the production and consumption of these legumes.

This article examines the potential of many obscure legume plants for future sustainable agricultural solutions to hunger and nutritional challenges, as well as genetic and molecular approaches promoting their wider usage and adaptability in modern agriculture.

One of the most urgent concerns of the time is ensuring everyone has enough to eat. The nutritional, agronomic, economic and ecological ramifications of relying so heavily on a small number of essential basic crops have limited global food security over the years (16). Stunted growth (especially in children under the age of 5) as well as child and infant mortality are largely attributable to malnutrition (17). Reduced economic growth and productivity are the result of both under nutrition (leading to stunted growth, underweight and mineral and vitamin deficiency) and over nutrition (leading to cancer, diabetes mellitus, stroke and heart disease) (12). The World Health Organization (WHO) reports that 462 million people are underweight, 115 million children under the age of five are stunted, 41 million youngsters are overweight or obese and 1.9 billion adults are overweight or obese. Disease rates worldwide may be lowered by 32% if malnutrition were reduced (12). Abnormal fetal brain physiology and morphology have been linked to malnutrition, particularly protein shortage (18). Death rates, medical expenses, and recovery times are all impacted by poor nutrition (19–22). Nutrient-rich but often overlooked legumes can improve both health and food security (23). They are low-cost and a good source of protein at a time when the consumption of animal products is prohibited due to potential health risks. Consequently, there has been an increase in the promotion and endorsement of plant-based protein as a means of satisfying the demands of the people (3). Beans, lentils, chickpeas, peas, and soybeans are currently some of the most widely farmed and consumed legumes. The Americas, Asia, and Africa are just some of the places where these legumes are cultivated. Numerous legume types exist that are underutilized since they are not as commonly grown or consumed as the big legumes. These legumes are not only an excellent food source, but also beneficial to soil health and erosion control. In conclusion, large legumes are notable for being an essential food crop and staple in many parts of the world. In addition to their potential to boost food security and soil health, underutilized legumes are a valuable resource in and of themselves. Bambara groundnut (Vigna subterranean), Jack bean (Canavalia ensiformis), Lima bean (Phaseolus lunatus), and sword bean (Phaseolus edulis) had their nutritional profiles analyzed by Soetan and Adeola (24). The nutritional needs of humans can be adequately met by consuming plants like Cassia hirsuta L., which has a high protein, lipid, potassium, fiber, carbohydrate, and energy content (24–26), and velvet bean (Mucuna pruriens), which has optimal crude protein, lipid, fiber, carbohydrate, energy, calcium, potassium, phosphorus, zinc, manganese, and magnesium content. Since different parts of underutilized legumes can be consumed, picky eaters can still get the same amount of nutrients. The blossom, seeds, pod case, immature pods, tuberous roots, and leaves of some underutilized legumes like winged bean, fenugreek, marama bean, and African yam bean are all edible. This confirms their wider usage over traditional legumes. The details of nutritional and anti-nutritional compounds in underutilized legumes have been furnished in Table 1.

The protein content of 104 legumes across 17 families was analyzed by Prakash et al. (27). Underutilized legumes ranged in protein content from 41 to 45%. Several species of Bauhinia and Canavalia gladiata had greater protein content than soybean. In terms of amino acids, both Bauhinia and Delonix are enriched in diverse amino acids. There is a wide variety of fatty acids in the seeds of tree beans (Parkia timoriana) and winged beans (Psophocarpus tetragonolobus) (26, 28). Legumes are an excellent source of carbohydrates, fiber, and ash, but are often overlooked. Indigofera linifolia’s nutrient and anti-nutrient composition was reported by Siddhuraju et al. (29) and significant amounts of protein (47.2–64.2 g/kg), lipids (56.7–72 g/kg) and fiber (27.6–31.9 g/kg) were reported. Unlike S. bispinosa, the seeds of I. linifolia are packed with nutrients. Albumins and globulins are found in I. linifolia seeds, while globulins and glutelins are abundant in S. bispinosa seeds. Although both species had sufficient levels of all other essential amino acids, they were deficient in sulfur containing amino acids (25, 26). Protein makes for 20.2–293.3% of a velvet bean, while lipids account for 6.3–7.4% and carbohydrates make up 49.9–61%.

Crude lipids, calcium, magnesium, and iron are found in Bauhinia malabarica seeds (30). The majority was glutamic acid (45%), with just trace amounts of cystine and methionine. Seed lipids were predominantly composed of oleic acid and linoleic acid. Vigna aconitifolia and V. vexillata were analyzed (29) and found with higher protein and mineral content. The crude fat content of V. aconitifolia seed was higher, while the amounts of cysteine and methionine were lower. However, V. aconitifolia has oleic acid and palmitic acid while V. vexillata does not. Canavalia’s biochemical composition and nutritional value was evaluated (29) and the seeds were found to contain 31.8–36.0% protein. There is a wide range of digestible starch content (70.6–71.8%), fatty acids (71–78%) and dietary fiber (17.5–23.6%) among Canavalia species. Canavanine content ranged from 27% in C. gladiata to 42% in C. ensiformis. Furthermore, Ayerdi and Marraccini (18) determined that the crude protein, fat, fiber, and carbohydrate contents of Cassia hirsuta ranged from 15.52–21.74, 3.77–7.04, 4.68–6.92, and 62.45–70.16%, respectively. The calorie content per 100 grams of seeds was reported to vary between 1549 and 1634. The crude seed protein content of Cassia obtusifolia ranged from 18.52 to 22.93%, with lipids making up 5.37–7.40% and carbohydrates accounting for 57.00–60.69%. Most of the protein in the seeds was found to be globulins.

Legumes’ resistance to disease is enhanced by anti-nutrients like polyphenols, tannins, saponins, amylase inhibitors, protease inhibitors, phytic acids and lectins. Raffinose, stachyose, and verbascose can all be found in legumes. Potentially unintended consequences (31) lead to their low consumption. Legume plants contain the anti-nutrient terpenes, amongst all, saponins are sugar-containing triterpenes found in legumes such as lentils, chickpeas, soybeans, and broad beans (32). Seeds are high in proteinaceous anti-nutrients called phytohemaglutinins or lectins, which agglutinate red blood cells (33). Legumes include compounds that impede the activity of enzymes like trypsin inhibitors (34). Phenolic compounds are the most abundant class of plant defense secondary metabolites and act as anti-nutrients due to their ability to form complexes with proteins and digestive enzymes. Tannins, complex polyphenolic chemicals, reduce nutrient absorption, and are found in high concentrations in underutilized legumes. Legumes whose tannin content is high may not be as appealing as they otherwise would be. Phytic acids are present in legumes and regulate the body’s ability to absorb nutrients. They facilitate the use of proteins and are the primary source of phosphate in most seed crops. Phaseolus lunatus and Phaseolus vulgaris, respectively, have been found to contain sapogenol. Lima beans, jack beans, African yam beans, and pigeon peas are all good plant sources of the α-galactoside (35). The removal of anti-nutrients is possible through careful processing (36) that can reduce anti-nutrient components in legumes, making them safe for human consumption. It is possible to aid underutilized legumes in adapting by selecting and domesticating suitable genotypes based on anti-nutritive compounds. Thanks to advancements in biotechnology; allergenic proteins and secondary metabolites have been significantly diminished (37). Improved adaptation and long-term viability of underutilized legumes can be achieved through genome editing or marker-assisted breeding (38). Underutilized legumes are not used more widely due to a lack of knowledge, research funding, and academic interest. The existing agricultural system only allows for the cultivation of a selected few crops, yet even these have contributed to efforts to improve national and international food security. In the contemporary movement to end world hunger and improve nutrition, the use of non-traditional food sources is a fundamental tactic. The collection, preservation, and propagation of germplasms, followed by the selection of crops based on quality parameters, can improve food security.

Orphan crops are generally more adapted to the extreme soil and climatic conditions may thrive in hot, dry climes, even when grown in rain-fed circumstances on marginal soil that exist in many parts of the world than are the major world food crops. Thus, understanding and deciphering the genetic foundation for these remarkable traits can be helpful in transferring elite characters to current growing cultivars. A plant’s morphological and physiological traits can be altered as a kind of adaptation in response to drought. Some of the ways plants react to drought include shrinking their leaves, sealing their stomata, altering the proportion of their biomass that is found in their shoots and roots, and modifying their roots (47–49). In response to drought stress, legumes’ root systems grow and are distributed in ways that optimize their ability to survive (50, 51). Root development in legumes accelerates throughout the vegetative growth stage but slows down after seed filling occurs in order to maximize the plant’s ability to take in as much soil moisture as possible (52, 53). Enhanced drought resistance in legumes has also been linked to a higher root hydraulic conductivity, which is influenced by the size and arrangement of the plant’s meta-xylem vessels (54). For instance, chickpea (Cicer arietinum) is a grain legume with a significantly lower root length density than barley (Hordeum vulgare), yet superior hydraulic conductivity allows the legume to more efficiently absorb water (55). Similarly, certain tepary bean (Phaseolus acutifolius) lines have deeper roots, with the biggest root mass located near the base of the soil profile. This improvement in water uptake is a direct outcome of the adaptations that have evolved. Lower stomatal conductance and smaller leaves are two further adaptive features of the bean that help it conserve water (56). Due to their hardiness and the soil microorganisms in their rhizosphere and nodules, underutilized legumes may tolerate harsh circumstances. Underutilized legumes contain unique physiological constitution and bacteria that can live and be active in harsh environments like salt, drought, pH, temperature, etc (14, 57, 58). Degefu et al. (59) found that, Bradyrhizobium elkanii and Bradyrhizobium japonicum thrive in salty and drought-stressed soils in Ethiopia and assist the pigeon pea plant. Inducing salt tolerance in mung beans with auxin and ACC deaminase-producing Pseudomonas and Rhizobium strains is also studied in details (60). Common bean was also tested for its capacity to thrive in a salty environment. Rhizobium species PvMb1, ISRA352, PvNk7, and PvNk8 alleviated salinity stress and increased plant growth and osmolyte content (glycine, betaine, and proline) (61). Rhizobium radiobacter from mung beans developed extracellular polymeric compounds to bioremediate arsenic and promote plant life and stress tolerance (62). Rhizobium-tolerant common beans also tolerate salt and pH. HUCRM3B, HUCRM2D, HUCRM5C, and HUCRM9C assisted common bean reduce pH and salt stress in their nodules (63). Bioremediation can be employed to put underutilized land to good use and the existence of microflora in very saline and acidic soils is evidence that these microorganisms thrive in these conditions. Pigeon pea can endure long periods of drought; thanks to its deep roots and osmotic adjustment in the leaves. Polycarpic flowering permits the crop to shed reproductive components while still maintaining photosynthetic activity, unlike drought-tolerant legumes like cowpea (64). Grass peas can withstand high water levels, low moisture levels, and moderate salt (65). The plant’s strong and extensive root system allows it to survive in nutrient-poor soil despite its fine texture, neutral to alkaline pH, and heavy clays (65). Maintaining soil fertility and reducing production costs are two benefits of grass pea’s nitrogen-fixing capabilities (65). Cowpea is a multipurpose plant grown in Africa, Asia, the Americas, and southern Europe due to its resilience in the face of adversity (66). Due to its ability to withstand acidic and alkaline soil conditions as well as its high mycorrhizal symbiosis and adequate SNF (solids not fat) levels, cowpea is tolerant to soils with low fertility (66). Cowpea may thrive in poor, sandy soils (67). In the semiarid tropics and subtropics, such as parts of Asia, Africa, Latin America and the Caribbean, pigeon pea is cultivated as a grain legume. It has a large window of maturity (90–300 days), is highly drought-resistant, and can be grown in a wide variety of climates (68). Pigeon pea’s high tolerance for acid soils and high efficiency of P uptake make it particularly exceptional (64). Future rhizofiltration systems may benefit from grass pea’s ability to retain large amounts of lead in its root tissues (69). The drought resistance of lentil, an annual legume crop used all over the world, makes it especially valuable in semiarid environments (70). The grass pea is an annual crop that serves two purposes (grain and forage) and is incredibly hardy in the face of adverse weather (71). For the rapidly growing populations in Asia and Africa, particularly in drought-prone and impoverished regions, it is one of the most promising sources of energy and protein. It’s a great option for diversifying cropping systems in Europe, Australia and the United States because it requires so few external resources (71). In “Adapting Agriculture to Climate Change,” Kew’s Millenium Seed Bank and the Global Crop Diversity Trust prioritize grass peas (72, 73). Drought-resistant grass peas are “insurance crops” for over 100 million Asian and African farmers (71). Unlike marama bean, grass pea was reported to resist drought and dehydration by modifying its maturity time, green leaf area and stomatal conductance (74, 75). Grass pea resists pests, diseases, and abiotic stress (75, 76) by producing ODAP (Oxalyldiaminopropionic acid), phenolic, flavonoid, and antioxidant compounds (72, 77) under stress conditions by scavenging the hydroxyl radicals (78).

Like soybeans and groundnuts, marama beans are high in protein and oil (79, 80) and its tubers can store water and lack nitrogen fixing nodules, thus can survive under water and nitrogen limited conditions (81). Osmotic adjustment and other drought avoidance strategies help the marama survive in extremely arid environments (82). Furthermore, plants produce many secondary metabolites and proteinaceous inhibitors to defend against environmental stresses (83). Marama bean produces a serine protease inhibitor (10.5% of its protein) which affects proteolytic activities leading to better performance in water-scarce conditions (84).

The UN’s Food and Agriculture Organization (FAO) recently estimated that food and nutrition insecurity affect 800 million people, mostly in developing nations (85). One of the Sustainable Development Goals (SDG) of the 2030 Agenda, which the United Nations endorsed in September 2015 (86), was to eradicate hunger and malnutrition worldwide, with a focus on less developed nations (87). Underutilized legumes have the potential to significantly contribute to numerous SDGs by providing a highly nourishing and sustainable food supply that can aid in the fight against hunger and poverty, especially in third world nations and by promoting sustainable agriculture that is adaptable to a wide range of agroecological and production systems, requiring few, if any, synthetic fertilizers or pesticides in their cultivation. Additionally, underutilized legumes have great potential to boost food production and soil health, both of which have a positive impact on adapting to the effects of climate change and other environmental issues. Furthermore, underutilized legumes offer numerous social and economic advantages. Promoting biodiversity and incorporating underutilized crop species into peoples’ diets and food habits is a practical strategy for tackling this problem (88). Underutilized legumes have enormous genetic potential, and genetic erosion or the loss of important genetic resources is concerning. The identification and application of untapped genetic resources in the gene pools of minor crops need further study. Therefore, coordinated research efforts are required to stop the on-going loss of genetic resources among the underutilized legumes. According to recent reports, the underutilized legumes face a problem in developing efficient phenotyping and breeding methods (89). The low level of genetic diversity that breeding programmes have access to limits modern breeding efforts to increase disease resistance, quality and yield (90). Although grain legume seeds in gene banks contain a sizable amount of genetic variation, such diversity has not been completely tapped into in active breeding operations (91).

Throughout the review we have understood the importance of underutilized legumes in human and animal diets, role of underutilized legume’s in mitigating abiotic stress, fighting hunger, malnutrition and achieving nutritional security and the possibility of breeding stable, high yielding and resistant lines of different legumes. Moreover, the nutritional and anti-nutritional contents of these legumes help in solving the health related issues by supplying essential nutrients to humans through alternate yet necessary food sources. The major advantage of these underutilized legume’s is their ability to acclimatize to wide range of climatic conditions and evade the pest and disease problems through production of autoimmune secondary metabolites. The underutilized legumes are also rich source of proteins, vitamins, minerals, lipids, fiber and carbohydrates, which provide balanced diet in optimum quantities. They also have a major role to play in creation of employment and additional income source to rural population during periods of adverse drought and famine situations. Even though, the legumes have several agronomic and nutritional advantages over the staple cereals, but they are not gaining much popularity because of several drawbacks, like, lack of knowledge regarding these legumes among the consumers, trivial cultivation in rural areas, poor government support for production and marketing, underfunding of researches related to underutilized legume’s, over dependence on staple cereals for food security, poor accessibility to genetic materials of underutilized legume’s and non-tapping of genetic diversity of underutilized legume’s in breeding programme.

Considering the nutritional and climatic significance; the cultivation and consumption of underutilized legumes has to be encouraged by several means to achieve both food and nutritional security. The cultivation of underutilized legumes can be enhanced by provision of good quality seed material, marketing facilities and creating awareness among the consumers. Although underutilized legumes can help increase food security and lessen poverty, they aren’t always easy to sell to consumers. Not being as popular or widely consumed as other important crops like rice, wheat, or maize is a key obstacle for underutilized legumes. Because of this, marketing and selling these legumes might be challenging because they are less well-known among consumers. Some customers may be put off by the fact that underutilized legumes differ in taste, texture, and nutritional profile from more common crops. There are, nevertheless, numerous openings for the promotion and widespread adoption of underutilized legumes. Another option to boost the marketability and appeal of underutilized legumes is to process and value-add them into flour, protein powder, or other food products. Food safety and quality are other aspects that affect the marketability and customer acceptance of underutilized legumes. Growing and processing underutilized legumes using safe and sustainable practices, and then cleaning, inspecting, and packaging them properly will boost their chances of being accepted by customers. The research activities related to breeding of underutilized legumes can be funded and exhilarated. The expeditions need to be conducted throughout the world to collect germplasms of underutilized legumes and enrich their genetic diversity. The detailed study on nutritional and anti-nutritional qualities of underutilized legumes can be carried out to understand their role in human diet. Use of information on genomics, proteomics, transcriptomics and metabolomics of underutilized legume’s for breeding, pest, disease and climate resilient lines need to be encouraged. In a variety of ways, advanced breeding procedures highlighted in this review can be very beneficial for strengthening underutilized legumes. Here are a handful of such examples:

Thus, in conclusion, it would rather be right to say, that legumes are the future crops that can tolerate the biotic and abiotic stresses created by anthropogenic climate change and provide the staple food for ever increasing population. Further, their inclusion in the daily diet plan can create a healthy and stable food option for both under nourished and over nourished population. Finally, the underutilized legumes can form a major subject of second green revolution, concentrating both on food security and nutritional security of the world.

TB, IS, MR, PM, and DJ: conceptualization, writing – original draft preparation, and preparation of tables and supervision. SM, AKP, DK, AUP, and PG: preparation of figure and review and editing. All authors read and approved the manuscript.