Genet Resour Crop Evol https://doi.org/10.1007/s10722-020-01023-1 (0123456789().,-volV) ( 01234567 89().,-volV) NOTES ON NEGLECTED AND UNDERUTILIZED CROPS Morphological and nutritional assessment of Vigna vexillata (L.) A. Rich.: a potential tuberous legume of India Kuldeep Tripathi . P. G. Gore . A. Pandey . E. R. Nayar . C. Gayacharan . R. K. Pamarthi . R. Bhardwaj . A. Kumar Received: 30 April 2020 / Accepted: 16 September 2020 Ó Springer Nature B.V. 2020 Abstract Vigna vexillata (L.) A. Rich. is a tropical tuberous legume which is fascinating for multiple uses in India. It is a climate-resilient legume and reported as a source of bruchid resistance, abiotic stresses tolerance and proteinaceous tubers. Meagre information is available for storage roots (tubers) of V. vexillata in general in the Indian scenario. In the present study, the evaluation of morphological and nutritional traits of storage roots are presented along with the genetic resources study. Herbarium study verified its wide distribution and occurrence in India since ancient time. Significant variability was observed for tuber morphological traits and nutritional parameters. Among accessions studied, IC259504 was identified promising agronomically and nutritionally both. Protein content in tubers of V. vexillata was recorded up to eightfold higher than that in sweet potato and tapioca. Results indicated that this species has the potential to meet the future needs of food and nutritional security and further utilization in Vigna improvement programme. Keywords India
Potential
Protein
Root tuber
Tuber cowpea K. Tripathi (&)
P. G. Gore
A. Pandey
E. R. Nayar
C. Gayacharan
R. K. Pamarthi
R. Bhardwaj
A. Kumar ICAR-National Bureau of Plant Genetic Resources (ICAR-NBPGR), New Delhi 110 012, India e-mail: kdtripathi89@gmail.com Introduction Vigna vexillata (L.) A. Rich (subgenus Plectrotropis; family Fabaceae) is a potential and under-exploited legume known by several names viz. tuber cowpea, zombi pea, wild cowpea, etc. It is pan-tropical herbaceous legume occurring in major continents Africa, Asia, Australia and America. In India, it is found in the hilly-subhilly tracts of peninsular India and the Himalayan region in the protected and partly disturbed areas. Southern Africa and South-east Asia are reported as primary and secondary centres of diversity, respectively (Wong 1997). V vexillata, a wild species closely related to the cowpea [Vigna unguiculata (L.) Walp.] is used for its storage roots, protein-rich seed, forage and erosion control plant (Hacker et al. 1996; Garba and Pasquet 1998). It is one of the underutilized legumes with potential for commercial exploitation. In India, it is locally called Halunda (Marathi), Banoria Urahi (Assamese), Kattupayar (Malayalam), Mudgaparni (Sanskrit) and Latchai (Bengali). Its fusiform roots are eaten raw or boiled in tribal pockets of Indian hills (Arora and Pandey 1996) and considered superior to sweet potato in flavours and nutrition (Arora 2014). Variability in germplasm was observed in sub-temperate, western and eastern ghats and north-eastern hills (Arora and Nayar 1984; Patiri and Borah 2007; Nandikar et al. 2018). Many of the developing world’s households depend on root and tuber crops as an essential source of food and nutrition (Scott et al. 2000). Leading tuber 123 Genet Resour Crop Evol crops are domesticated from non-legume species such as potato, sweet potato, cassava and yam. Tuber cowpea is one of the few species of Vigna viz. V. lobatifolia and V. marina that produced tuberous roots. It is usually a vigorous twining or scrambling vine with large, showy purple or purplish-yellow flowers with fleshy tuberous roots from which the plants perenniate. In its range of occurrence, V. vexillata is collected from the wild or it is cultivated for its tubers in African and Asian countries. Two domesticated forms have been reported; seed type and tuber (storage root) types. The seed type is believed to be domesticated in Sudan (Africa), while Indonesian region extending to India is believed to be the domesticated centre for tuber type (Bhattacharyya et al. 1984; Asati and Yadav 2004; Dachapak et al. 2018). Among various domesticated species of Vigna, tuber cowpea is one of the least researched crop for its genetic resources, especially in the Indian region. Despite its value, African collections have received more attention than that from south-east Asia, including India (Damayanti et al. 2010). Surprisingly, meagre information is available for its tuber diversity and nutrition. The nutritional divide among communities of rich and poor people is increasing and leading to an alarming situation, especially in the developing countries of Africa and Asia. In this climate-changing scenario, the dietary diversity is also an integral component of food as well as nutritional security. Realizing the potential of V. vexillata, the present study was undertaken to assess selected tuber types of germplasm available in the Indian national genebank using morphological and nutritional parameters for direct use as well as in Vigna breeding programme. Materials and methods Experimental materials A total of 108 accessions of V. vexillata were obtained in the form of seed from the Indian national genebank, ICAR-National Bureau of Plant Genetic Resources (ICAR-NBPGR), New Delhi. During summer 2018, all accessions were grown in the net house of ICARNBPGR farm (Lat. 28° 630 N; Long 77° 150 E) to delineate tuberous forms from the non-tuberous ones. The seeds were scarified mechanically to ensure maximum germination. Subsequently, in summer 123 2019, seeds of selected accessions with diverse tuber morphology (seven in number) were again grown at ICAR-NBPGR farm for the present study (Fig. 1). Seeds were sown directly, and excess seedlings were thinned to leave two plants per pot. Each plant was provided with a bamboo stake for support, around which they were hand-trained during growth to prevent intertwining. Fresh tubers were harvested from each accession for recording morphological and nutritional data. Herbarium study Herbarium voucher specimens were prepared following standard procedures (Victor et al. 2004; Pandey 2019) and deposited in the National Herbarium of Cultivated Plants (NHCP), New Delhi. Micro-morphological characters were studied using the Stereoscopic Zoom Microscope (Nikon SMZ1000) at ICARNBPGR, New Delhi. Information on distribution and uses of the plant was validated from literature and herbarium study. The identity of the accessions was confirmed through the critical examination of the plant at various growth stages and matching characters with the data in floristic literature (Hooker 1879; Cooke 1903; Gamble 1928; Kanjilal et al. 1938; e-flora India 2006; Yadav et al. 2014). Besides, the herbarium specimens available in the Botanical Survey of India (BSI) and the virtual herbaria at London (BM!), Edinburgh (E!), Kew (K!), Paris (P!) and Beijing (PE!) and India (BSI!, NHCP!) including the type specimens were used. Morpho-nutritional evaluation of tuber As there are no exclusive descriptor for tuber cowpea, tuber morphological traits were recorded with the help of sweet potato descriptors which was published jointly by International Potato Center (CIP), Peru; Asian Vegetable Research and Development Center (AVRDC), Taiwan and International Board of Plant Genetic Resources (presently Bioversity International), Rome (CIP, AVRDC, IBPGR 1991). A total of seven qualitative traits was recorded such as tuber surface, tuber skin colour, tuber branching, storage root surface defect, storage root shape, storage root cracking and tuber flesh colour; three quantitative traits viz.. tuber length, tuber width and tuber weight were measured. Genet Resour Crop Evol Fig. 1 Variability in leaf, pod, seed and tuber of accessions of V. vexillata The proximate composition was determined using the official methods (AOAC 2016) viz. moisture (AOAC 934.01), ash (AOAC 938.08), dietary fibre (AOAC 985.29), protein (AOAC 2001.11) and fat (AOAC 920.39). Sample preparation for total sugar, total starch and total phenols was done as described by Manivannan et al. (2018). 100 mg of dried and homogenized samples were extracted thrice with 5 ml of 80% (v/v) ethanol at 60 °C for 60 min. After each extraction samples were centrifuged at 5000 g for 15 min and the supernatant was pooled. The extract was dried in boiling water bath, dissolved in water for estimation of sugar (Buysse and Merckx 1993) and phenols while the residue of the sample from 80% ethanol extraction was used for starch estimation (Chow and Landhäusser 2004). Total soluble sugar content in the extract was determined using the anthrone reagent method (Hedge and Hofreiter 1962), and starch content was estimated as per AOAC 996.11. Determination of Total Phenol Content in the extract was done using Folin-Ciocalteu (FC) assay as described by Singleton et al. (1999) with slight modifications and the results were expressed as gallic acid equivalent (GAE). Antioxidant activity was 123 Genet Resour Crop Evol measured as cupric ion reducing antioxidant capacity (CUPRAC) of the extract and determined according to the method of Apak et al. (2004). Phytate content was measured by enzymatic procedure using phytic acid assay kit (K-PHYT) from Megazyme, Ireland. Statistical analysis All morphological traits were measured in quintuplicate for each accession. Statistical analysis was done using SAS 9.3 and Duncan’s Multiple Range Test (DMRT) to ascertain significant differences for each trait between different germplasm studied. Result and discussion Botany V. vexillata is a strong slender twiner, stem (1.5–2 m) usually covered with spreading silky hairs; leaves trifoliate, leaflets 4.5–14.7 9 2–7.2 cm (IC259504 was with the broadest leaflet), ovate, acute at apex; petiole 3–4 cm long; flowers light purple, solitary or 2–4 together; calyx 8–9 mm long, petals light purplish; standard 25 9 30 mm, orbicular, wings 20–22 9 12–18 mm, keel 20-25-18-28 mm long, strongly spurred on lateral side; pods 4–14 9 2–5 mm, densely brown-hispid, 4–12 number of seeds per pod; aril developed; flowering and fruiting occur in August to December. V. vexillata is considered to be a ‘linking’ species with affinities to both the African Vigna (subgenus Plectrotropis) and Asiatic Vigna (subgenus Ceratotropis). It is close to cultivated cowpea, V. unguiculata (Garba and Pasquet 1998). Development of V. vexillata 9 V. unguiculata hybrids using embryo rescue techniques (Gomathinayagam et al. 1998) and partial fertility with green gram indicates that it belongs to the tertiary gene pool of several cultivated Vigna spp. (Evans 1975). This species is highly diverse in morphological differences, and up to eight varieties have been described for zombi pea (i.e., vexillata, angustifolia, dolichomena, davyi, yunnanensis, plurifora, lobatifolia, and ovata) (Marechal et al. 1978; Pienaar and Kok 1991; Maxted et al. 2004). It is believed that taxonomic identity of Vigna species is complicated and still there is a need of detailed characterization to develop keys based on 123 global collections (Babu et al. 1985; Gore et al. 2019). An illustrated guide for genus Vigna identification were developed by Yadav et al. (2014), but it was limited to few accessions. Domesticated form of V.vexillata reported from sub-Saharan Africa, Sudan, Ethiopian highlands, Transvaal etc. in Africa, Indonesia and India in Asia. Another cultivated form V.vexillata var. macrosperma was described from the specimen from Costa Rica (Marechal et al. 1978). V. vexillata is available throughout the country from western Himalaya to north-eastern hills up to 2500 m altitude (Hooker 1879). As per passport data of Indian national genebank, germplasm of V. vexillata is widely represented from Latitude 9° 100 N (Nicobar island) - 34° 080 N (Kashmir); Longitude 72° 00’ E (Rajasthan)93° 85’ E (Arunachal Pradesh). Maximum diversity is present in the western ghats followed by peninsular India and hill region. Maharashtra topped the chart in term of number of accessions (21) collected, followed by Andhra Pradesh (18). Herbarium examined Around 150 virtual herbarium specimen images from eight major e-herbaria (BM!, E!, K!, P!, PE!, CAL!, NHCP!, & RRL) including the type specimens were consulted for the identity, morphological variability in plant characters. Herbarium specimens very rarely included below-ground parts. Some specimens showed the tubers and notes on edibility. Out of specimens from Botanical Survey of India (BSI), specimens showed the record on edibility from wild specimens. Specimen no. 446 (Fig. 2A) from Sikkim on 01.10.1862 by T. Anderson which evident the availability of the particular species since long time in Indian sub-continent. Specimen no. 115395 (Fig. 2B) from Maharashtra in 1968 and specimen no. 5938 from Khasi hills of Meghalaya in 1915, both the specimens noted the edibility of tubers. Of which, some specimens (37244, Parasnath wildlife sanctuary, Jharkhand); 16109, Indravati Tiger reserve, Chhattisgarh; 127941, Valley of flowers, Uttarakhand etc.) collected from protected areas such as reserve forests and wildlife sanctuary which indicated the presence of V. vexillata widely occurred in the wild in India. Furthermore, specimen (no. 62265 (Dt. 05.05.1979) and no. 64437 (Dt. 08.10.1979) of this species collected twice in different months of the same year Genet Resour Crop Evol Fig. 2 Herbarium specimens of V. vexillata: a Herbarium specimen no. 446 b Herbarium specimen no. 115395; (Ó The Director, Botanical Survey of India. Reproduced with the consent of Central National Herbarium, BSI, Howrah, India) indicated that this species flowered twice in a year in the southern India. Voucher herbarium (HS24240 of EC697161) was prepared as per standard procedure and deposited in the NHCP at ICAR-NBPGR, New Delhi. Morphological variability in tuber A total of seven diverse accessions of tuber cowpea was grown for characterization of tuber morphological traits. Since there is no descriptor for tuber characterization of V. vexillata, sweet potato descriptors was used to characterize tuber of V. vexillata accessions. Morphological variability in tuber is depicted in Fig. 3. During morphological characterization of tuber, significant variability was observed for traits such as tuber length, tuber width and tuber weight. Tuber weight ranged from 3.5 to 100.05 g, and highest tuber weight per plant was recorded in IC259504. Tuber length and width were ranged from 1.8 to 28 cm and from 0.4 to 4.0 cm respectively (Fig. 4). IC259504 was recorded with maximum tuber weight and tuber width while it was second-longest in tuber length. IC259504 was a macrosperma type collected from Goa state of India. In qualitative traits, there was no storage root surface defect observed among the accessions. Narrow ring flesh was observed in crosssection of all accessions of tuber cowpea. There was no variability in tuber flesh colour; all accessions were recorded with white flesh colour. Storage root 123 Genet Resour Crop Evol Fig. 3 Variability in tubers of V. vexillata cracking was not visualized in indigenous accessions. EC697161 and IC259504 had irregular storage root shape. Variability in tuber surface, tuber skin colour and tuber branching was depicted in Fig. 5. Tuber branching was observed in three out of seven accessions whereas five accessions had rough tuber surface. Three descriptor states were reported for tuber skin colour viz.. white (EC697161), pink (IC278014), and rest possessed creamy white. Tuber formation started from close to the soil surface in IC259504 whereas, in other accessions, it started lower than that of IC259504. Pandey et al. (2019) reported in soh-phlong that tuber formation started from more closer to the surface in domesticated type than wild type. The morphological characterization attempted by previous researchers was mainly based on flower, leaf and seed characters but hardly any study on the tuber traits. Popoola et al. (2017) characterized and evaluated 26 accessions of V. vexillata and worked out interrelationship among the morphology for cowpea improvement based on 26 traits of the vegetative, floral, pod and seed. Grant et al. (2003) assessed a total of 79 accessions of V. vexillata for a range of agronomically important characteristics, including tuber associated traits. They observed the least variation in tuber morphology in comparison to seed and pod traits. Based on the study, he concluded that accessions of V. vexillata was relatively homogeneous across the wide geographical range within Australia. Damayanti et al. (2010) also reported less diversity in tuber morphology after evaluating diverse accessions representing Africa, Australia and Indonesia. Though less variability in tuber reported by previous workers, but the present study reported a wide range of morphological variations among selected tuber bearing accessions. IC259504 was found different from other indigenous accessions which may be due to climatic adaptation. Vargas et al. (2017) concluded in his study on sweet potato, many factors, such as growing season, soil, water, used germplasm, plant nutrition, etc. were responsible for variations in tuber traits. Fig. 4 Graphical representation of quantitative traits (a) Tuber length and width (b) Tuber weight 123 Genet Resour Crop Evol Fig. 5 Symbolic representation of variation of tuber surface, branching and skin colour among the accession of V. vexillata. Symbols used R = Rough, S = Smooth, W = White, C = Creamish, P = Pink According to Gonçalves et al. (2011), most of the modern sweet potato cultivars were selected for home consumption, and there is a vast potential for other purposes. Similarly, dedicated research is still needed to identify germplasm of tuber cowpea for home consumption, livestock feed, vegetable and medicines. Nutritional evaluation Result of ten important nutritional quality traits analyzed as per AOAC methods are presented in Table 1. Wide variability among accessions were recorded for all proximate traits. Protein content (%) was ranged from 7.64 ± 0.006 to 9.93 ± 0.13. Two accessions viz.. IC277055 and IC259504 were found with more than 9.5% protein content while EC697161 with least protein content. Being a leguminous tuber, protein is the most important useful trait for enhancing utilization of this crop. Negi and Gaur (1994) reported 14.5% protein content in the dry roots of V. vexillata, however they did not give any details about accessions and experiments. Fat content (%) of accessions varied from 0.31 ± 0.06 to 1.12 ± 0.067 and showed significant (p \ 0.05) differences among the accessions. 123 107.85a ± 0.86 In any column, values with the same superscript letter are not statistically different according to DMRT at 5% * 123.89c ± 0.55 0.989 ± 0.05 0.756a ± 0.05 51.86f ± 0.39 31.37 ± 0.80 ± 0.02 14.04 12.89b ± 0.56 3.31f ± 0.02 1.22 ± 0.01 4.92 ± 0.06 4.19c ± 0.02 0.328a ± 0.015 0.781 ± 0.019 1.94a ± 0.02 7.64a ± 0.05 9.63 ± 0.10 2.00 ± 0.01 70.95 ± 0.47 74.06c ± 0.55 IC259504 EC697161 121.07c ± 0.89 128.87d ± 1.76 0.960 ± 0.01 c b 28.30 ± 0.32 14.49 ± 0.63 bc a 1.43 ± 0.01 4.72 ± 0.03 f c 0.311 ± 0.006 8.33 ± 0.01 f a 2.46 ± 0.07 69.20 ± 0.15 IC203618 b c 1.207 ± 0.06 ± 0.99 67.43 a c 11.29 ± 0.26 2.71 ± 0.03 b e ± 0.03 5.29 0.730 ± 0.029 a c 7.90 ± 0.03 ± 0.01 2.06 d a 69.28 ± 0.45 IC278014 113.89b ± 0.67 ± 0.06 0.890 d g 35.37 ± 0.35 ± 0.04 13.69 a e 1.61 ± 0.03 4.41 ± 0.04 g c 1.126 ± 0.067 8.68 ± 0.05 b ab 1.94 ± 0.03 72.09 ± 0.20 IC247405 a bc c bc c d e d 160.55e ± 1.16 2.14b ± 0.06 a 160.38e ± 0.64 2.29c ± 0.02 71.06b ± 0.04 71.77b ± 0.32 IC277034 IC277055 b 0.923c ± 0.02 0.968c ± 0.05 41.33e ± 0.59 43.77d ± 0.23 13.21b ± 0.03 13.24b ± 0.32 1.17a ± 0.01 2.05d ± 0.01 3.93b ± 0.03 3.63a ± 0.09 0.554b ± 0.005 0.976d ± 0.017 ± 0.13 (%) (%) 8.96e ± 0.03 g Sugar (%) Dietary fibre(%) (%) Fat Protein (%) Ash Moisture Acc. No. Table 1 Nutritional profile of tubers of accessions V. vexillata 123 9.93 (lg/g GAE) (%) Phytate Starch (%) Phenol (mg/100 g) Antioxidant Genet Resour Crop Evol It was reported earlier with 0.9% fat content (Negi and Gaur 1994). Ash content was observed significantly higher in IC203618 (2.46%). Among the selected accessions, IC278014 significantly contained the highest amount of phenol content (67.43 mg/100 g), whereas IC203618 contained the lowest amount. IC278014 was collected from comparatively cooler areas in north-eastern India and recorded with light pink tuber skin colour. Natural phenolic compounds have drawn huge attention due to additional advantages of reducing the risk of several diseases due to their antioxidant activity together with other healthpromoting factors. The polyphenol content can vary among foods, and the level of it could be influenced by environmental factors, the degree of ripeness and other factors, such as type of soil, the degree of exposure to sun and rainfall. In sweet potato tubers, high phenolic content was observed at locations with longer days and cooler temperatures (Alam et al. 2016). IC277055 recorded the highest value for CUPRAC activity. The dietary fibre content also has shown considerable variation among the accessions studied. The lowest dietary fibre content was recorded in IC277034 (3.63%) and highest in IC278014 (5.29%). Starch content also has shown a great range of variability with the minimum of 11.29% in IC278014 to maximum being 14.49% in IC203618. EC697161 was found with highest sugar content but least in protein, fat, ash, phytate and antioxidant. Nutritional compositions were also compared with other major tuber crops viz.., sweet potato, cassava and soh-phlong, a minor leguminous tuber from India (Table 2). Nutritional data on sweet potato and cassava were extracted from Indian food composition table published by National Institute of Nutrition, India (Longvah et al. 2017) whereas recent study published for Flemingia procumbens Roxb. (sohphlong), a leguminous tuber from north-eastern India were studied to collect quality data (Pandey et al. 2019). IC277055 of V. vexillata were selected to compare due to its highest protein content. In comparison to other crops, tuber cowpea was found to have seven-fold and nine-fold higher amount of protein content than sweet potato and cassava respectively but threefold to soh-phlong. Dietary fibre content was almost similar to sweet potato. Dietary fibre has recently received much importance, as it is reported to diminish the incidences of colon cancer, diabetes and cardiovascular diseases (Ingabire and Genet Resour Crop Evol Table 2 Comparative nutritional profile of tuber cowpea studied and reported in other tuber crops S.N. Proximate components V. vexillata (IC277055) 1 Protein (%) 9.93 ± 0.13 2 Starch (%) 13.21 ± 0.03 3 4 Fat (%) Sugar (%) 5 Moisture (%) 6 Ash (%) 7 Dietary fibre (%) Sweet potatoa Tapiocaa 3.25 ± 0.90 1.03 ± 0.10 18.82 ± 1.74 21.8 ± 5.96 15.36 ± 0.12 0.26 ± 0.06 3.63 ± 0.05 0.55 ± 0.07 0.27 ± 0.08 0.20 ± 0.01 2.14 ± 0.05 71.77 ± 0.32 69.21 ± 0.83 62.4 ± 10.4 75.23 ± 0.55 2.14 ± 0.06 0.96 ± 0.07 0.11 ± 0.7 1.12 ± 0.11 3.93 ± 0.03 3.99 ± 0.054 4.32 ± 1.03 4.61 ± 0.12 0.97 ± 0.017 2.05 ± 0.01 1.33 ± 0.121 Soh-phlongb a Source: Indian Food Composition Tables, 2017, NIN, Hyderabad b Source: Pandey et al. (2019) Vasanthakaalam 2011). The local germplasm of tuber cowpea in subsistence production systems are still prevalent in tribal pockets of India despite their negligible commercial market system. Many of these germplasm are under continuous cultivation because of their unique taste, medicinal and nutritional qualities. Sasikumar and Sardana (1988) reported proximate compositions on seeds of tuber cowpea, but they did not give any information on tubers. Karuniawan et al. (2006) emphasized to do further research aiming at the collection of additional accessions from unexplored places, the characterization of the nutritional quality of tuber alongwith seeds, leaves and hybridization efforts between other accessions of the V. vexillata genepool and cowpea. High nutritional potential was assessed based on chemical analysis and nutritional assessment of the less known pulses V. aconitifolia (Jacq.) Marechal and V. vexillata (L.) (Siddhuraju et al. 1994). The study carried out on the biochemical and nutritional composition of seed of V. vexillata from Southern Western Ghats of Tamil Nadu, India (Siddhuraju et al. 1994, 2000; Kalidass and Mohan 2011) but few data is available on the nutrient and biochemical composition in the Indian context. Uses and domestication trends Fresh young shoots, green seeds and tubers are used as vegetables (Irvine 1977; Padulosi and Ng 1990; Karuniawan et al. 2006). On-farm root yields of 18–30 t ha- 1 and seed yields of 0.7–1.2 t ha- 1 were estimated (Karuniawan et al. 2006). Its herbage is used as a fodder or cover crop (Skerman et al. 1988), dry seeds used as a dry pulse (Sasikumar and Sardana 1988) and plant parts are used for medicinal purposes (Burkill 1985; Rana and Samant 2011). The purified principles of V. vexillata were potential to be developed as new anti-inflammatory drugs through the inhibition of PI3K or NADPH oxidase (Leu et al. 2012). V. vexillata used in local cuisine preparations by native people of Australia (Grant et al. 2003; Sprent 2009). Globally, most reports of production and use of the crop have been from subsistence and tribal agriculture. Research interest in tuber cowpea to date has been mainly in estimating its suitability as a source of genetic diversity for other Vigna species, particularly cowpea (V. unguiculata), and around fifty accessions in current international germplasm collections are explicitly identified as cultivated varieties (Damayanti et al. 2010). V. vexillata is considered as a donor for cowpea improvement because of resistance to bruchids, flower thrips, pod borer and Striga gesnerioides, powdery mildew and cowpea mottle virus. Additionally, it shows high levels of resistance to various abiotic stresses, such as waterlogging and alkalinity (Marubodee et al. 2015). Despite this wide range of potential uses, the crop remains orphan in terms of active crop improvement research, apart from some minor breeding attention as a pasture legume. The domestication study of tuber cowpea is of particular interest because two cultivated forms of this legume have experienced different domestications from wild V. vexillata. Seed type was domesticated from Africa, while the tuber type was domesticated from Asia (Dachapak et al. 2018). Local name Kattupayar means beans of forest which indicates its presence in wild habitat and Latchai is due to resemblance to cowpea. Other local names available 123 Genet Resour Crop Evol in floristic literature such as Janglee lobia, Suryaparni, Machali, Halunda, Mudgaparni in parts of India indicate its well-known status as a potential useful legume. Among many wild consumed species, V. vexillata is used for suppressing hunger (Yesodharan and Sujana 2014). It is used as a tuber and pulse in north-east India (Bhattacharyya et al. 1984) and the foothills of Himalayan regions (NRC 1979; Sasikumar and Sardana 1988). Sasikumar and Sardana (1988) also reported that cultivation of V. vexiallata as a good cover crop cum intercrop for rubber plantations in India. It is a well known tribal pulse of Western Ghats, Tamil Nadu (Kalidass and Mohan 2011) and central India (Siddhuraju et al. 1994). The seeds are consumed as pulse and tubers cooked as a vegetable in Assam, India (Patiri and Borah 2007; Dutta et al. 2017) or seeds eaten after roasting (Siddhuraju et al. 1994). Traditional uses of V.vexillata in the diet by ethnic communities of Tripura, India is linked with the socioeconomic development of the state (Chakraborty et al. 2019). Due to its high protein in seed and tubers in the north-eastern hill region of India, its value was realized four decades ago (Bhattacharyya et al. 1984; Sasikumar and Sardana 1988) resulting in wide cultivation in these areas. There was no seed dormancy reported, but some degree of pod shattering was known. Cultivated forms of V. vexillata were reported from several localities in Bali and West Timor in Indonesia, where the crop is adapted to drought compared with other traditional, non-legume, root crops (Karuniawan et al. 2006). Occurrence in the Himalaya and the foothills of India in the wild all over and also in the kitchen garden for use by the tribal indicated the trends of domestication in the protected habitats. Conclusion This study allows a glimpse into the variability in tubers of the Indian region. V. vexillata is widely distributed in all four biodiversity hotspots designated in India. Despite low variability in tubers reported globally, this investigation revealed sufficient variation for tuber morphology, nutritional traits and habitat study. Utilization of existing variability can lead to improvement in V. vexillata as a root crop besides pulse, vegetable and forage crop. In the past, local communities mainly depended upon a wide range of 123 species to fulfil their food and health security. It is therefore needed to revive the old dietary traditions by paying attention to orphan species rich in nutrition like V. vexillata. There is thrust to be laid on a dedicated and systematic exploration programme to collect wild and semi-wild materials from untapped areas of India. Development of descriptors for Distinctness, Uniformity and Stability (DUS) traits would be beneficial for evaluation of tuber cowpea accessions. Identification and validation of useful traits linked with accessions of V. vexillata will facilitate their effective utilization in Vigna improvement programme. Acknowledgements Authors express their sincere thanks to the Director, ICAR-NBPGR, New Delhi, for guidance as well as for providing all available help rendered during the study. Thanks to the Director, Botanical Survey of India (BSI) and Head, CNH and especially Dr A. Bhattacharjee for providing herbarium images. First author also thanks Dr Saroj Sardana for sharing information about her previous work. Compliance with ethical standards Conflict of interest Authors declare that they have no conflict of interest on the content of the manuscript and study undertaken. References Alam MK, Rana ZH, Islam SN (2016) Comparison of the proximate composition, total carotenoids and total polyphenol content of nine orange-fleshed sweet potato varieties grown in Bangladesh. 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