Spatial Distribution, Diversity Mapping, and Gap Analysis of Wild Vigna Species Conserved in India’s National Genebank

Abstract

The genus Vigna has several crop species that could be used to feasibly address nutritional security challenges in the subtropical and tropical regions of the world, particularly in climate-changing scenarios. Wild taxa of Vigna are a source of economically important traits and need to be studied. Out of the 34 wild Vigna species reported in India, 928 indigenous accessions belonging to 19 wild Vigna are conserved in India’s National Genebank (INGB) housed at the National Bureau of Plant Genetic Resources, New Delhi. Geospatial mapping has identified diversity-rich areas and the Western Ghats region exhibits the highest Shannon diversity values (H = 1.65–3.0). Using the complementarity procedure, six diversity hotspots were identified for the 34 wild Vigna, and these require utmost priority for exploration and germplasm collection. Due to the meagre amount of information available for wild Vigna, the BioClim model was used to successfully predict the Idukki district of Kerala as a suitable site for germplasm-collecting expeditions. Coastal areas identified as rich in twelve wild taxa, V. bourneae, V. dalzelliana, V. marina, V. sublobata, V. subramaniana, V. vexillata, V. stipulacea, V. trilobata, and V. trinervia, require immediate attention to protect hotspots as well as to collect accessions from these areas for ex situ conservation. A hotspot in the protected forest of Anshi National Park and Bhagwan Mahavira Wildlife Sanctuary was identified as an ideal spot for possible in situ conservation of V. konkanensis, V silvestris, and V. sublobata. The 15 wild Vigna species do not have representation in the INGB, and 11 Vigna species have been identified as endemic species to India. Priority needs to be given to these species for focussed exploration and germplasm collection. This paper discusses the future focus on explorations to be carried out for the collection of the germplasm of wild Vigna species.

1. Introduction

The genus Vigna has more than 200 species distributed across subtropical and tropical regions of the world [1,2]. Vigna species exhibit a wide distribution in India from the seacoast to high-altitude areas of the Himalayas. There are 34 wild Vigna species, subspecies, and varieties [3,4,5] and several cultivated species, including the Adzuki bean [Vigna angularis (Willd.) Ohwi & H. Ohashi], Moth bean [Vigna aconitifolia (Jacq.) Maréchal], Black gram [Vigna mungo (L.) Hepper], Green gram [Vigna radiata (L.) Wilczek], Cowpea [Vigna unguiculata (L.) Walp.], Rice bean [Vigna umbellata (Thunb.) Ohwi & H. Ohashi], and Yard-long Bean [Vigna unguiculata subsp. sesquipedalis].

Wild taxa are important for crop plants due to their indirect use derived from their relatively close genetic relationships with crops and crop progenitors, mainly belonging to the primary gene pool (GP-I or GP-II) of the group [6,7]. Crop wild relatives (CWR) of crop plants are a potential source of disease-resistance genes and have greater adaptability to biotic and abiotic stresses. India, with 34 taxa of the wild Vigna, is considered a secondary center of species diversity for the genus Vigna [1,5]. Thirty-one taxa have been reported [4] for the six Vigna groups, whereas new Vigna species reported in India are V. yadavii S.P. Gaikwad, R.D. Gore, S.D. Randive & K.U. Garad, V. pandeyana R.D. Gore, S.P. Gaikwad & S.D. Randive [8,9,10]; V. konkanensis (Willis) Janard [11]; V. sathishiana Balan & Predeep [12]; and V. khandalensis (Santapau) Raghavan & Wadhwa [13]. The researcher described 34 taxa including 29 species, one subspecies, and four varieties of wild Vigna [5]. In addition, V. angularis var. nipponensis (Ohwi) Ohwi & H. Ohashi Tateishi & Maxted distribution was reported by Arunachal Pradesh and Mizoram [14].

Changes in the climate and irregular rainfall patterns not only pose major challenges for food security [15] but also for the management of CWR and their ecosystems. It is estimated that the temperature will rise in the range of 1.4 °C to as much as 5.8 °C by the end of 2100 in the wake of the global climate change regime [16]. In this situation, different wild Vigna species are likely to be highly affected by changes in niche habitats, mainly due to habitat loss, forest degradation, and the encroachment of wild habitats. Therefore, the identification of locations/diversity hotspots for wild Vigna species in different biodiversity-rich areas of India should be a top priority for conservation and collecting.

GIS tools have been significantly used in diversity distribution mapping and also enhance the efficiency of management of PGR by generating new information through spatial analyses of the exploration, evaluation, characterization, and georeferencing of location/site data [16,17,18]. Spatial information on species richness, distribution, and the abundance of common beans (Phaseolus spp.) was studied. The diversity and spatial distribution of wild potatoes (Solanum spp.) in 16 countries around the world were analyzed using the georeferenced database [19]. In India, several GIS-based studies have been conducted for diversity assessment, such as the assessment of pod characteristics in black gram [20] and the species distribution and mapping of the diversity index of Piper species [21]. This tool was also used for georeferencing, assessing the diversity distribution and species richness, and grid mapping in Brassica spp. collected from different states of India [22]. GIS tools to map the trait-specific germplasm in pigeon pea and the geographic distribution of rice landraces from the Western Ghats region of India, respectively, were used for the gap analysis [23,24].

Gap analysis is a systematic method of analyzing the degree of conservation of taxa, to identify collection sites and particular traits (adaptation) in unsecured or under-secured conservation systems [25]. The gap analysis also helps to determine which areas are under-collected or over-collected for germplasm related to the known distribution of a taxon [26]. Geospatial technologies have expedited a better understanding of species distribution and the representativeness of germplasm collection and have contributed to the conservation planning of wild crop relatives [27].

The present work is a novel attempt to provide insights about wild Vigna genetic resources in India with respect to (i) the germplasm collection status of different taxa of wild Vigna; (ii) the prioritization and diversity mapping of wild Vigna based on collected germplasm data; (iii) the identification of diversity-rich hotspots areas using complementarity procedures; and (iv) habitat prediction mapping for wild Vigna.

2. Materials and Methods

2.1. Study Area, Scrutiny of Passport Data, and Georeferencing

More than 460 thousand accessions of plant genetic resources are conserved in India’s national genebank housed at ICAR-National Bureau of Plant Genetic Resources, New Delhi (ICAR-NBPGR), with about 40 thousand CWR accessions. There are 928 Vigna CWR accessions belonging to V. sublobata (279), V. trilobata (172), V. vexillata (125), V. stipulacea (100), V. dalzelliana (76), V. bourneae (Gamble) Tateishi & Maxted (34) and V. silvestris (Lukoki, Marechal & Otoul) Aitawade, K.V. Bhat & S.R. Yadav (29), V. ternervia (26), V. hainiana (20), V. reflexopilosa (18), V. angularis var. nipponensis (14), V. khandalensis (13), V. marina (5), V. glabrescens and V. nepalensis (3 each), V. luteola (Jacq.) Benth (2), V. adenantha and V. vexillata var. wightii (Benth. ex Bedd.) Babu & S.K. Sharma (one each) [28]. These Vigna CWR accessions were collected from 24 states of India, showing a wide genetic base of the wild Vigna species in India (Figure 1). Information on the conserved germplasm accessions (i.e., the crop name, IC number, local name, collector number, collector name, location data, etc.) is usually documented in a passport database. The location is usually specified by the country, state, and at least one administrative subdivision (e.g., district) and by a description of the locality (village or panchayat name) from where the accessions were collected. The majority of the germplasm collection data contain area information (village/block/tehsil/district/state) and geocoordinates (lat. and long.) recorded by a global positioning system. Gaps in the collection site coordinates were filled by information from secondary sources (gazetteer, Survey of India map, etc.) and subsequently used in georeferencing and diversity distribution mapping. Herbarium specimens (491 specimens of different wild Vigna species) were also consulted for recording additional collection site information [29], which was then utilized in a complementarity analysis.

Before diversity mapping and analysis, the passport data were thoroughly scrutinized and checked with respect to the geocoordinates of the sites of collection (village/block/taluk/district) using GIS tools [18,19]. The botanical names were corrected using websites https://powo.science.kew.org, https://theplantlist.org (accessed on 18 July 2022), e-floras, and floras. Since 1999, several new states and districts have been formed either by merging some parts or dividing large parts of existing states and districts. Therefore, in the present study, the correct geographic identity was reassigned and coordinates in decimal degrees were incorporated in each accession, forming a rationalized georeferenced map of the wild taxa of the Vigna genus.

2.2. Diversity Mapping Based on Grid Mapping

DIVA-GIS tools have been widely used for the ecogeographic mapping of collection sites, the diversity distribution of crops, and wild species. This software consists of a geographic projection system and WGS84 geodetic systems (datum) for linking the locations of sampled regions on the map. The GIS-based grid mapping technique has been used to identify diversity-rich areas, conduct a variability assessment, and determine the occurrence of the trait-specific germplasm [16]. A grid of definite size is assigned on the map to the points representing the collected germplasm. The grid size depends on the size of the geographical area (district/state/region). At the country level (large geographical area), the grid is 1° × 1° (111.321 × 111.321 km) in size, while for states/subdivisions (smaller area) a grid of 0.2° × 0.2° to 0.9° × 0.9° is used, depending upon the area and diversity [18]. To determine the spatial distribution and assess the species richness, DIVA-GIS is used for point data conversion into a grid analysis using simple circular neighborhood methods [16], and the diversity is calculated using the Shannon–Weaver diversity index [30] through the following formula:

H = −∑ [(ni/N) ln (ni/N)]

H = Shannon diversity index, ni = individual of a species, N = total individuals of all species

2.3. Diversity-Rich Area Selection Based on Complementarity Analysis

The complementarity diversity-rich area selection procedure aims to identify grid cells that complement each other and that capture the maximum amount of diversity in as few grids as possible [16]. The procedure is based on the algorithm described entirely in [31]. A spatial analysis was performed using DIVA-GIS software. The species diversity was estimated using the different classes (richness) and identifying diversity-rich hotspots using the iterative procedure [32] in the ‘reserve selection’ manner to locate optimal locations to identify new diversity hotspots using a 70 × 70 km² grid cell. In the present study, the same grid cell size (70 × 70 km²) was used for both reported (34 species) and conserved (19 species) wild Vigna species. The procedure is based on iterations of different grid cells of the same size. A site for the new diversity hotspots of a CWR species was recommended based on germplasm collected during the last four decades and a complementarity analysis.

2.4. Habitat Prediction Mapping Using the BioClim Model

The WorldClim dataset [33] is an advanced method used for global environmental characterization, as it provides high-resolution (i.e., nearly 1 km) climatic variables derived from historical records from several weather stations across the globe (http://www.worldclim.org, accessed on 28 March 2023). BioClim, a species distribution model implemented in DIVA-GIS version-7.5 [34], is interfaced with climate data (19 Bioclimatic variables) for temperature suitability or temperature-derived data: BIO1 = annual mean temperature; BIO2 = mean diurnal range (mean of the monthly (max. temperature – min. temperature); BIO3 = isothermality (P2/P7) (*100); BIO4 = temperature seasonality (standard deviation *100); BIO5 = max. temperature of the warmest month; BIO6 = min. temperature of the coldest month; BIO7 = temperature annual range (P5–P6); BIO8 = mean temperature of the wettest quarter; BIO9 = mean temperature of the driest quarter; BIO10 = mean temperature of the warmest quarter; BIO11 = mean temperature of the coldest quarter; rainfall-derived data: BIO12 = annual precipitation; BIO13 = precipitation in the wettest month; BIO14 = precipitation in the driest month; BIO15 = precipitation seasonality (Coefficient of variation); BIO16 = precipitation in the wettest quarter; BIO17 = precipitation in the driest quarter; BIO18 = precipitation in the warmest quarter; BIO19 = precipitation in the coldest quarter. The BioClim model was applied to determine the species distribution using the current climate data (1950–2000) derived from WorldClim; climate grids with a spatial resolution of 2.5 km² were used as baseline data [33]. Habitat prediction maps were drawn based on collected data and climatic variables.

3. Results

3.1. Georeferencing of Wild Vigna Germplasm and Distribution Mapping

A georeferenced map of 928 accessions showed their distribution pattern in the Western Ghats (Gujarat, Maharashtra, Goa, Karnataka and Kerala) and Eastern Ghats (mainly Andhra Pradesh and Odisha). The maximum distribution of wild Vigna species was recorded from the peninsular region (12 taxa) compared to other regions (seven taxa) in the country (Figure 1). More than 60% of the wild taxa of the Vigna germplasm were collected from the peninsular region of the country. Out of the eight states in the peninsular region, only Odisha and Telangana have less than 15 germplasm accessions of wild Vigna species. Seven taxa, namely V. angularis var. nipponensis, V. nepalensis Tateishi & Maxted, V. trinervia (B. Heyne ex Wight & Arn.) Tateishi & Maxted, V. vexillata and V. reflexopilosa Tomooka & Maxted, and V. sublobata were collected from the northeastern hill (NEH) region, a biodiversity hotspot area with high endemism. It has also been observed that V. angularis var. nipponensis, and V. nepalensis are found only in NEH regions. V. hainiana Babu, Gopinathan & S.K. Sharma, V. sublobata, V. trilobata, and V. vexillata were collected from the Western Himalayas (Himachal Pradesh, Jammu & Kashmir, and Uttarakhand). V. glabrescens Marechal, Mascherpa & Stainier was collected from the Palamu district, Jharkhand in a part of eastern India. Four wild taxa, V. dalzelliana, V. trilobata, V. sublobata, and V. vexillata, were collected from the eastern Ghats region (Andhra Pradesh and Odisha) of India. V. marina (Burm.) Merr., V. dalzelliana, V. trilobata, V. sublobata, and V. vexillata were also collected from the A&N Islands, which are mostly dominated by sandy clay and sandy loam soil types. The database also revealed that wild taxa of the Vigna species germplasm have been collected from diverse habitats such as contiguous fields, forests, shrubs, degraded lands, fallow land, hilly areas, and the coastal regions of the country.

3.2. Diversity Mapping of Wild Taxa of the Vigna Using the Shannon–Weaver Diversity Index

An analysis of INGB data revealed the conservation of a significant number of germplasm accessions (571 accessions) for major wild taxa of Vigna species. Maximum accessions were conserved for V. sublobata (186) followed by V. trilobata (101), V. vexillata (101), V. stipulacea (100), V. dalzelliana (33), and V. bourneae (15) (Figure 2). In contrast, one accession each for V. adenantha (G. Mey.) Marechal, Mascherpa & Stainier, V. glabrescens, V. minima (Roxb.) Ohwi & H. Ohashi, V. khandalensis, V. marina, and V. luteola are present in the genebank. The GIS-based grid mapping based on multiple diversity indices identified diversity-rich areas with different diversity values (Figure 3). Dark red grids (H= 1.68–3.00) represent regions with higher diversity/greater number of species (V. vexillata, V. dalzelliana, V. khandalensis, V. marina, V. sublobata, and V. hainiana) collected from these sites; yellow to orange colored (H = 0.83–1.166) areas represent regions with a moderate number of species (V. trilobata and V. minima); while dark green to light green (H = 0.00–0.42) areas represent regions with minimal species (Vigna bourneae, V. nepalensis, V. marina, V. trinervia, and V. silvestris). The mapping of diversity (value H = 1.68–3.0) indicated that some of the diversity-rich areas, for example, parts of the Idukki, Palakkad, and Thrissur districts of Kerala and the Belagavi, Dharwad, and Uttar Kannada districts of Karnataka are diversity-rich hotspots, which are parts of the WGR (Figure 3). The region comprises more than 12 species of wild Vigna. It extends from 8.32° to 21.23° N in latitude and 72.91° to 77.15° E in longitude, and along with the West coastal part, comprises 42 districts in the states of Gujarat, Maharashtra, Goa, Karnataka, Kerala, Rajasthan, and Tamil Nadu. The region starts in southeast Gujarat and ends near Kanyakumari, Tamil Nadu [35]. Based on the application of the Shannon diversity index, which displayed high diversity values, it was also discovered that diversity-rich hotspots were spread outside of the WGR, including portions of the Banaskantha district in Gujarat and the Jalore and Sirohi districts in Rajasthan. All parts of Goa and Kerala in WGR need to be explored for the collection of wild taxa of the Vigna species through priority-based explorations.

3.3. Identifying Diversity-Rich Hotspots for 34 Wild Vigna Species in India

Based on the species richness and complementarity procedure, grid maps were generated for all 34 taxa of wild Vigna species reported in India. The available data showed that the wild taxa of Vigna species are distributed from the Northwestern Himalayas to the Eastern Himalayas and the Western Plain (Rajasthan) to the Western Ghats and A&N Islands. However, the highest species concentration is found in the WGR (Gujarat, Kerala, Goa, Karnataka, Maharashtra, Rajasthan, and Tamil Nadu). The complementarity analysis for all wild Vigna species showed that the major diversity-rich pockets are found in the western and southern parts of Maharashtra and central Kerala, with 14–18 taxa (Figure 4 and Figure 5). Following the complementarity procedure for all wild Vigna species, diversity-rich hotspots were identified in different states, such as Kerala (parts of Ernakulam, Malappuram, Palakkad, and Thrissur districts), Goa (north Goa district), Maharashtra (parts of southern Kolhapur and Sindhudurg districts), Karnataka (southern parts of Belagavi district and northern parts of Uttar Kannada district), Gujarat (northern parts of Banaskantha and Kutchh districts), Rajasthan (southern parts of Barmer and Jalore districts), Nagaland (Kiphire, Noklak and Phek districts), and the A & N Islands (North and Middle Andaman districts). These diversity-rich areas require immediate attention to protect hot spots as well as to collect accessions from these areas for ex-situ conservation.

3.4. Identifying Hot Spots for Augmenting Wild Vigna Species Conserved in the Genebank

GIS maps were generated for 19 wild taxa of the Vigna genus conserved in the genebank showing that wild Vigna species are distributed from North-Western Himalaya to Eastern Himalaya, Western arid region, Western Ghats and A&N Islands. However, the highest species concentration (9–11 taxa) was found in the WGR (Figure 6). The major diversity-rich hotspots were identified in Central and southeast Kerala (parts of Ernakulam, Malappuram, Palakkad and Thrissur districts), and parts of Western Ghats with species concentration (8–10 taxa). Based on the complementarity procedure using genebank data, diversity-rich hotspots were identified in Kerala (parts of Ernakulam, Malappuram, Palakkad and Thrissur districts), Madhya Pradesh (Raisen, Sagar and Vidisha districts), Nagaland (Kiphire, Noklak and Phek districts) and A&N Islands (North and Middle Andaman districts) except in Maharashtra, where two diversity-rich hot-spots are identified—the first containing the Pune, Ahmednagar, Satara and Solapur districts and the second containing the Kolhapur and Sindhudurg districts (Figure 7). It was clear that out of >110 grids of equal size, only six grids from different states represented the most diversity-rich hot spots, each with a maximum of 8–10 taxa. The gaps were obvious, and this information may facilitate the prioritization of expeditions for collection and conservation.

3.5. Prediction of Habitats for the Collection and Conservation of Wild Vigna Species

A habitat suitability map of wild Vigna species was generated based on occurrence data and interpolated with 19 bioclimatic variables using the BioClim model interfaced with the DIVA-GIS system. The predicted habitat suitability map based on the past climate (1950–2000) showed that a highly suitable area was generated for wild Vigna species, spread over four states (Andhra Pradesh, Odisha, Bastar region of Chhattisgarh and western parts of Telangana) of India. The maximum predicted area was in Odisha (55.0% of the total highly suitable area estimated for the target area), followed by Andhra Pradesh (28%), Chhattisgarh (14.5%), and Telangana (2.5%) (Figure 8). The GIS map shows the predicted areas for additional ex-situ conservation of the 19 taxa prioritized in the wild Vigna genus that need to be relooked for collection in all five states, because the area is prone to natural calamities. It was observed that mainly hilly areas, coastal areas, shola forests, aquatic areas, and hot subhumid to semiarid ecoregions with coastal alluvium-derived soils are the major distinct ecosystems possessing specialized niches for CWR [36]. The east and west coasts of India are prone to frequent natural calamities, such as cyclones, heavy winds and floods, high rainfall events, and seawater intrusion where prioritized wild Vigna expeditions are needed for targeted collection.

Being an excellent soil conservation crop, V. adenantha has a twinning or trailing perennial herb, a tuberous rootstock, and pinkish-violet flowers. It is distributed mainly in the A&N Islands, Bihar, Madhya Pradesh, Odisha, Tamil Nadu, and West Bengal. Collections of V. glabrescens were made from Jharkhand and Uttar Pradesh, while distributions have been recorded in parts of Odisha and West Bengal. An extensive survey and collection of germplasm are required to establish new distribution records. It is a robust, erect herb with large golden-yellow flowers. V. minima was collected from the Goa part of the Western Ghats and is also distributed in China, Malaysia, Japan, and New Guinea. V. marina, also known as beach pea, is a prostrate, creeping vine that is a perennial species of coastal regions. The flowers are yellow and have a pea-like shape. In India, it is distributed in Nicobar and the south Andaman Islands, particularly in hot humid to sub-humid ecological subregions with shallow to medium depth loamy to clayey red and red loamy soil in coastal regions of the country [37]. Vigna stipulacea has mostly been collected from parts of Andhra Pradesh, a peninsular part of southern India. High humidity and temperature are necessary for its growth, which makes it a preferred fodder legume in both summer and rainy seasons, while Vigna vexillata was mainly collected from hilly sections of the Western Ghats and the northeastern Himalayas. Based on data from the collected and conserved germplasm and a critical review of the literature (Flora and Herbarium specimens), tangible gaps and areas identified for the collection of wild Vigna species across the country are given in

Table 1. Collection gaps and areas identified for the survey, exploration, and expedition of wild Vigna species based on collected and conserved germplasm data.

Wild Vigna	Areas identified Based on Gaps in Collections
Germplasm collected but less conserved
V. bourneae (Gamble) Tateishi & Maxted	Dakshina Kannada and Udupi districts of Karnataka; Kottayam, Mallapuram, Palakkad, and Thrissur districts of Kerala and Tamil Nadu
V. hainiana * Babu, Gopinathan & S.K. Sharma	Sidhi and Singrauli districts of Madhya Pradesh; Hazaribagh and Lohardaga districts of Jharkhand and Chittaurgarh and Pratapgarh districts of Rajasthan
V. trinervia (B. Heyne ex Wight & Arn.) Tateishi & Maxted	Kottayam and Thrissur districts of Kerala, parts of Karnataka and Tamil Nadu
Species-wise least collection
V. khandalensis * (Santapau) Raghavan & Wadhwa	Parts of the Nashik, Pune, Satara, and Ratnagiri districts of Maharashtra and parts of Gujarat
V. marina (Burm.) Merr	Andaman and Nicobar Islands–Swaraj and Neil Islands, Kerala, Odisha, Tamil Nadu and Lakshadweep.
V. minima (Roxb.) Ohwi & H. Ohashi	Northeast India and parts of Chhattisgarh
V. nepalensis Tateishi & Maxted	Phek and Tuensang districts of Nagaland and Eastern Himalaya and other parts of northeast India
V. silvestris (Lukoki, Marechal & Otoul) Aitawade	Parts of Madhya Pradesh, parts of the Raigad, Ratnagiri, and Sindhudurg districts of Maharashtra and parts of south Goa, Karnataka, and Rajasthan
Areas representing deficit collection
Eastern Himalayas	Subtropical areas of Assam, Meghalaya, Mizoram, and Tripura
Western Himalayas	Subtropical, mid and Shiwalik hills, Bhawar and Terai areas up to 1800 msl, altitude
Desert	Desert scrub, thorny scrub areas Aravali hills
Coastal regions and Islands	West Bengal-24-South Parganas and Sunderban areas; Andaman & Nicobar Islands–Swaraj and Neil Islands
Western Ghat	Nilgiris and adjoining areas (1500 to 1800 msl)

* Endemic species.

.

4. Discussion

4.1. Habitat Prediction Mapping Facilitates Germplasm Collection

Studies using the BioClim model could identify suitable areas within and beyond the known range of occurrence in the case of Eurayle ferox L. in India [24] and Nothofagus cunninghami (Hook.) Oerst. in Australia [38,39] within and beyond the known range. Because of the meagre information available for wild Vigna, this study used the BioClim model to successfully predict WGR, particularly the Idukki district of Kerala, as a suitable area for germplasm collection expeditions. This area is home to niche-specific and sparsely populated species suffering from seed-shattering problems, such as V. angularis var. nipponensis, V. nepalensis, V. vexillata var. sepiaria, V. vexillata var. stocksii, V. sathishiana, V. subramaniana, and V. vexillata var. wightii, so this location demands special attention from taxonomists and explorers.

4.2. Wild Taxa of Vigna Species Occurring in the Coastal Regions of India Need Urgent Attention

Coastal regions in India are facing a severe threat from factors such as inundation, seawater intrusion, changes in soil salinity, and tropical cyclones [37]. Twelve wild taxa of the Vigna species, V. bourneae, V. dalzelliana, V. marina, V. sublobata, V. subramaniana, V. vexillata, V. stipulacea, V. trilobata, and V. trinervia exist in these vulnerable coastal areas. Immediate attention is required to protect hotspots identified in the study and collect/recollect accessions from these areas for ex-situ conservation. Further, it has been reported that wild Vigna species such as V. silvestris, V. trinervia, V. sublobata, and V. vexillata are potential sources of resistance to Mung bean Yellow Mosaic Disease and bruchids [40,41,42,43,44,45]. V. sublobata and V. marina are known to be tolerant to drought, salinity, and alkalinity [46,47,48]. Germplasm accessions of V. stipulacea, V. sublobata, V. trilobata, and V. vexillata are known to be adapted to high-temperature areas of the eastern ghat (Andhra Pradesh, Tamil Nadu) regions of the country. Trait-specific evaluation and utilization of these CWRs in breeding programs around the country may provide the necessary impetus for conservation efforts.

4.3. Identifying Diversity-Rich Hotspots for In Situ Conservation

Identifying diversity-rich hotspots using complementarity analysis is very helpful for discovering micro-diversity-rich areas. For instance, Lathyrus complementarity maps for the 36 priority species could be used to identify the areas on either side of the Lebanese/Syrian border near Tel Kazakh, Syria as priority locations for establishing an in situ genetic reserve [49]. A diversity-rich hotspot in the Uttar Kannada district of Karnataka falls in the protected forest of Anshi National Park and Bhagwan Mahavira Wildlife Sanctuary. This could be an ideal spot for the possible in situ conservation of V. konkanensis, V silvestris, and V. sublobata [50], and the A&N Islands could be used for V. marina. The 15 wild Vigna species do not have representation in the genebank; they should be the top priority for collection (

Table 2. Wild Vigna species not represented in the genebank that are priorities for collection.

Wild Vigna Species	Distribution	References
V. clarkei * Prain	Parts of Arunachal Pradesh, Assam, Sikkim and West Bengal	[5]
V. grahamiana (Wight & Arn.) Verdc.	Parts of Andhra Pradesh, Maharashtra, Mysore (Karnataka), Kannur, Kollam, Kottayam and Palakkad (Kerala); Coimbatore, Kanyakumari, Dindigul, Theni, Nilgiri, Salem, Tirunelveli and Salem (Tamil Nadu)	[5]
V. hosei (Craib) Baker	Parts of Pathanamthitta (Kerala) and Odisha	[5]
V. indica * T.M. Dixit, K.V. Bhat & SR Yadav	Maharashtra, Northwestern Ghat region, Endemic to India	[5,53]
V. konkanensis * Latha, K.V. Bhat, I.S. Bisht, K.J. John & Krishnaraj	Ratnagiri district of Maharashtra	[11]
V. mukerjeanus * (Babu ex Raizada) Raizada	Parts of Uttar Pradesh and Uttarakhand	[5,54]
V. pandeyana * R.D. Gore, S.P. Gaikwad & S.D. Randive	Chalkewadi in Patan tehsil, Satara district, Maharashtra, Northwestern Ghat region, Endemic to India	[9]
V. prainiana Babu & S.K. Sharma	Parts of Sikkim and Uttar Pradesh	[55]
V. sahyadriana * Aitawade, K.V. Bhat & SR Yadav	Northwestern Ghat	[4,5]
V. sathishiana * Balan & Predeep	Kollar dam site in Idukki district (Kerala) Endemic to Kerala	[12]
V. subramaniana * (Babu ex Raizada) M. Sharma	Parts of Madhya Pradesh, Punjab, Tamil Nadu and Uttar Pradesh	[5]
V. vexillata var. angustifolia (Schumach. & Thonn). Baker	Arunachal Pradesh, Throughout India	[4,5]
V. vexillata var. stocksii * Benth. ex Baker	Parts of central India, Eastern and peninsular India	[5]
V. vexillata var. sepiaria * (Dalzell) Babu & S.K. Sharma	Western Ghat region of India	[5]
V. yadavii * S.P. Gaikwad, Gore, S.D. Randive & Garad	Kasara Ghat, Igatpuri, Kalvan and Saptashrungi hills, Nashik, Thoseghar Satara, Maharashtra	[10]

* Endemic species.

). Of the 34 wild Vigna species, Table 2 describes 11 endemic species of the Vigna genus, which are only found in India, in detail, along with presenting the geographical information and priorities for imminent exploration and germplasm collection. Endemic species are those that are best adapted to a specific ecology, and such regions need to be given priority (Table 2). Among the 34 Vigna species, Vigna stipulacea and V. vexillata could be used for domestication and cultivation for food and foraging [51,52]. V. stipulacea is primarily used for pulse, fodder, and manure production in peninsular India, while it has been reported that V. vexillata was used traditionally in northeastern India and the Western Ghats. These species need to be promoted in peninsular India as summer crops to meet the livelihood security demands of local people in the region.

5. Conclusions

This study identified exploration gaps for wild Vigna species in different phytogeographic regions and diversity-rich areas of India using a complementarity analysis. This information can be used to support the planning of future explorations. An analysis of the wild Vigna species showed the highest Shannon’s diversity values (H = 1.65–3.0) for the Western Ghats region, which is one of the world’s biodiversity hotspot sites and a reservoir of wild Vigna species in India. Additionally, based on habitat prediction modelling, the Eastern Ghats regions of India have been identified as diversity-rich hotspots for capturing the diversity of wild Vigna species. The analysis also identified 11 endemic species, including vulnerable coastal regions that should undergo habitat conservation, as they are potential sites for in situ conservation of wild Vigna species, and we need to conserve these invaluable species.