Drought is a major challenge/constraint to achieving worldwide food security and production enhancement. Drought adversely affects plant growth at all developmental stages, impairing the morphology of the plant and the biochemical and physiological processes operating in the planted crops. These aspects subsequently affects, among others, the uptake of vital nutrients for plant growth and the ability of the seeds to germinate and of the plant to photosynthesize (Fahad et al., 2017; Lamaoui et al., 2018). Drought stress has negative consequences on the vitality and vigor of seeds and impairs seedling growth (Hatzig et al., 2018). The optimum growth/developmental stages in planted crops are adversely affected by drought, as observed in a decline in the rate of germination, seedling emergence and growth; impairments in vegetative growth, cell division and elongation; with mitotic processes also being affected (Farooq et al., 2009).

Drought stress can adversely affect the functioning of vital enzymes. Among other influences, the flowering stage of the plant could be negatively affected, as also the photosynthetic rate and the assimilate partitioning process. All these conditions eventually reduce the planted crop yields (Anjum et al., 2011).

Drought also impairs the proper functioning of the plant cell by producing oxidative damaging reactive species (ROS), which destroy plant lipids and proteins (You and Chan, 2015). Drought leads to adverse influences on the growth, development, and reproduction ability of planted cowpea, which limits the yield and productivity of the planted crops (Verbree et al., 2015; Daryanto et al., 2017; Ravelombola et al., 2018a).

Numerous studies have been done and are also on-going due to the enormity of drought stress challenges on cowpea productivity enhancement. In a study by Cui et al. (2020), they evaluated cowpea drought tolerance potentials at seedling stage. The experiment was done using a total of 36 cowpea-breeding lines in a completely randomized manner under drought stress conditions. Their results revealed that four (4) Arkansas cowpea breed lines are drought-tolerant, and they ranked better in terms of chlorophyll, healthiness and lodging score when compared to the other 32 genotypes. Therefore, these four cowpea breed lines could be further exploited in cowpea-breeding improvement. Also, in a study to highlight the constraining effects of drought stress on above-ground traits in cowpea plant, (Ravelombola et al., 2018a) assessed drought stress induced changes in 17 above ground traits in 30 cowpea genotypes at the seedling stage of growth for 28days. Their findings showed that cowpea genotypes PI293568, PI349674, and PI293469 are slow to wilting, better adapted to drought, while the other susceptible genotypes are fast to wilt, the chlorophyll content is lower, and they undergo senescence faster too. The three (3) cowpea drought-tolerant genotype could be exploited further for advanced breeding.

More so, in a comprehensive study of drought tolerance response in cowpea plant (Carvalho et al., 2019) used four (4) cowpea genotypes to determine their physiological, biochemical and molecular response under water-limiting stress conditions. The output from this study highlighted the importance of stomata conductance, photosynthetic parameters, compatible solutes like anthocyanin and proline, as well as increase in enzymatic activity of reactive oxygen species scavenging enzymes like catalase, superoxide dismutase, glutathione reductase, guaiacol peroxidase. This study also characterized the drought gene expression profile of the four cowpea genotypes. Thirteen drought related genes were profile, and some of the genes were expressed higher than others under drought stress. The hallmark of the study was that cowpea genotype Cp5051 was the most drought tolerant due to a higher expression of drought-tolerant marker genes VuHsp17.7 and VuCPRD14.

Soil salinity is a major abiotic constraint to plant productivity. Salinity adversely impacts the metabolic and physiological processes in plants. Statistical report stipulated that upward of over 45 million hectares of agricultural soil are affected by this problem and that climatic change, as well as current irrigation practices, will exacerbate this situation (Munns and Gilliham, 2015; Parihar et al., 2015).

In addition, salinity stress negatively influences the rate of plant growth. The adverse influence of salinity reduces the fresh and dry weight of plants, while other vegetative growth traits are also adversely impacted (El-Beltagi et al., 2013; Mohamed et al., 2018).

Salinity stress leads to extensive damage in the adductive capacity of planted crops. It reduces lipid peroxidation and leads to the production of destructive oxidation species (ROS), that in turn causes damage to the key plant biomolecules (Ghonaim et al., 2021).

Salinity stress ultimately reduces yields and the productivity of planted cowpea crops, thereby affecting the goal of achieving enhanced global food security (Da Silva Sá et al., 2017; Ravelombola et al., 2018b).

Research into the impact of salinity on cowpea has indicated that it impairs cowpea seed germination, its vigor, and growth (Zahedi et al., 2012; Mini et al., 2015).

In order to evaluate salinity stress impact on cowpea cultivars (Ravelombola et al., 2019), investigated a simple protocol that could be deployed to assess the response of 30 cowpea genotypes to salinity constraint at seedling growth stage in a greenhouse experiment that profile 14 above ground traits response to sodium chloride (NaCl)-induced salinity. The findings indicated that relative salinity tolerance (RST) of cowpea genotype PI255774, all the plants were completely dead, while PI582438 performed best and the leaves were all green and had higher chlorophyll content. The outcome of this study validated simple protocol of assessing chlorophyll content and leaf injury for assessing salinity at seedling stage in cowpea. Also, in a study to investigate further the utility of chlorophyll content as a means of assessing salinity tolerance in cowpea seedling over time, (Dong et al., 2019) investigated how 24 different cowpea genotypes responded to salinity induced stress by monitoring the chlorophyll changes over a period of 24days using a split-plot design. The results indicated the importance of genotype and the timing in relation to cowpea seedling response to salinity stress. Also, the chlorophyll content of the cowpea salt-tolerant cultivar was higher at day 24 of the experiment, while all the cowpea salt sensitive plant were dead at the end of the 24days. In addition, salinity induce stress could further predispose cowpea cultivars to viral infestation. In their study, (Varela et al., 2019) assessed the consequences of exposing a cowpea severe mosaic virus (CPSMV)-resistant genotype to salinity induced stress. The results signify that vital protein pathways were altered, and there was proliferation of the (CPSMV), leading to the cowpea genotype changing from resistant to susceptible.

Heavy metals pose serious environmental constraints for and can adversely impact on plants and humans when the former bioaccumulate in plants and ultimately reach human beings via the food chain (Sidhu, 2016).

Heavy metals pose environmental and public health threats when they are discharged as by-products of industrial processes in the form of effluents (Wuana and Okieimen, 2011). Heavy metals, such as cadmium (Cd), lead (Pb), arsenic (As), mercury (Hg), chromium (Cr), and antimony (Sb), affect plant productivity and plant yields.

Heavy metals adversely affect the metabolic processes of the plant during the course of its growth and development. Heavy metals negatively influence the germination of seeds, while the vegetative growth rate (leaf, shoot, and root) is also impaired. Plants are adversely affected by heavy metals, as in the case of various physiological and biochemical processes such as the rate of photosynthesis, the uptake of nutrients, vital enzymatic reactions, as well as in the case of emergence of ROS (Azevedo and Rodriguez, 2012; Tiwari and Lata, 2018).

Research reported by Asagba et al. (2019) detailed the impact of Nickel toxicity on cowpea germination and other biochemical parameters. The investigation on phytotoxicity of nickel at varying concentration on cowpea seedling growth rate, length, fresh weight, as well as Ca²⁺ ATPase activity was assessed. The results indicated toxic impact of this heavy metal on cowpea seedling agronomic and biochemical parameters.

Also, in a study by Ogunkunle et al. (2020) that applied co-inoculation of arbuscular mycorrhizal fungi (AMF) and nano-TiO₂ to reduced oxidative stress and bioaccumulation of Cd in cowpea, it was reported that the total chlorophyll of the cowpea plant, as well as different reactive oxygen species enzymes were impacted negatively due to Cd induced toxicity.

As an abiotic stress factor, temperature in the case of low temperatures (chill stress) and high temperatures (heating stress) is a potential constraint in limiting the productivity and yield of planted crops globally. Temperature is a key abiotic parameter that influences the growth and development of plants (Hatfield and Prueger, 2015).

High temperatures limit the photosynthetic rate of the plant. The vegetative growth parameters and the metabolic activities of the plant are also adversely affected. Also, emergence, maturity/ripening, harvesting time (length of period/stage), and plant yield are affected (Prasad et al., 2008; Shah et al., 2011). Likewise, low-temperatures (chilling stress) adversely influence plant metabolic activity and negatively impact the growth/development of plants (Tian et al., 2011). Low temperatures (chilling stress) also negatively affect the germination rate, seedling emergence, and the vigor of the plant, so that the productivity of the plant is ultimately reduced (Abbas, 2012).

In a study on the impact of elevated temperature on the agronomic growth parameters and the nutritional status of cowpea at different growth phase, (Nevhulaudzi et al., 2020b) reported that there were differences in both the agronomic growth and nutritional parameters, and this is more pronounced at the flowering and pre-flowering stage.

Waterlogging stress affects the gaseous exchange in agricultural soil and negatively impacts crop productivity globally. It leads to an insufficient supply of oxygen to the plant roots and this in turn reduces the growth and development of the plant roots. It also leads to the inability of the plant to take up the necessary nutrients and nitrogen. Waterlogging affects the photosynthetic rate, reduces the vegetative agronomic growth rate of plants, leads to the senescence of leaves, and ultimately, negatively affects crop yield and productivity (Ren et al., 2014).

Higher or excessive soil water availability do not always favor cowpea growth. In a field study done in the Sudan Savanna zone taking genotype environment interaction into focus, (Iseki et al., 2021) reported that excess water can inhibit the nitrogen-fixing capability of cowpea and lower its productivity.

Climatic changes in weather, as denoted by among others variability or fluctuations in the prevailing temperatures, rainfall, and the volume of greenhouse gases, are potentially limiting factors on various agro-input variables and ultimately affect the productivity of planted crops on a global scale (Awoye et al., 2017; Kukal and Irmak, 2018; Hounnou et al., 2019).

Climatic changes also adversely threaten the agri-food system at all scales: globally, nationally, regionally, and locally (Ajadi et al., 2011).

Climatic change negatively impacts agri-food input and output production systems because it influences the biotic and abiotic parameters of agricultural production. Hence, it affects planted crop yields (Challinor et al., 2014).

Changes in climatic conditions affect the biochemical, physiological, and metabolic activities of plants; the photosynthetic rate is affected, as are factors such as plant growth and development, and the rate of transpiration; there is also an imbalance in the elimination of CO₂, and a reduction in enzyme reactions; flowering may be affected, which could also lead to senescence (Srivastava et al., 2019). Predictive studies have forecast a reduction in food grain yields toward the later years of this current century (Pachauri et al., 2014), this hinging on expected extremes in global temperatures. Furthermore, most, if not all of the major food crops are adversely impacted by stress arising from heat at the different growth and developmental stages (Kaushal et al., 2016; Atlin et al., 2017). Global changes in climatic conditions have been found to adversely affect the health of humans, animal/livestock production, as well as planted crop productivity (Lesk et al., 2016; Mora et al., 2017).

In summary, many huge tasking constraints are militating against and slowing down the optimum yield production of cowpea in Africa. Some of these limiting challenges are highlighted in Table 2.

A major constraint in limiting cowpea yields can be attributed to bacterial pathogens, which lead to massive crop losses of upward of 70% in the form of seed grain, pod, and fodder reduction (Agbicodo et al., 2010). Some of these destructive pathogens are transmitted via the seed (De Lima-Primo et al., 2015), while some are transmitted via the soil-borne route (Constantin et al., 2016). Some of the damaging symptoms of bacterial pathogen infestation in cowpea are brownish leaf spots, necrotizing and yellow halo leaf shapes, cracks noticeable on the stem, and pods filled with water, and blotch (Claudius-Cole et al., 2014). Among the most destructive bacterial pathogens of cowpea are members of the Xanthomonas genus (Shi et al., 2016; Durojaye et al., 2019).

Nematodes are responsible for huge losses in cowpea production and are also one of the constraints limiting improvements in cowpea production (Haegeman et al., 2012; Dareus et al., 2021). This they accomplish by impeding the uptake of water and nutrients. Also, nematodes limit cowpea growth and development by interfering in the pathways towards cell differentiation and in the transportation of auxin (Gheysen and Mitchum, 2011). Meloidogyne javanica and Meloidogyne incognita are the two major nematodes destroying cowpea (Oliveira et al., 2012).

Fungal pathogens are the topmost destructive agents/phytopathogens of planted crops globally (Fisher et al., 2012). Very many species of different genera of fungi destroy cowpea in the field and during the post-harvest stage. Furthermore, seed and soil-borne fungal pathogens have been implicated in the loss of cowpea production that sometimes rises to 100% (Mbeyagala et al., 2014). Notable fungal pathogens of cowpea include Rhizoctonia solani, Colletotrichum spp., Fusarium oxysporum, Macrophomina phaseolina, and Sclerotium rolfsii (Adegbite and Amusa, 2010; Pottorff et al., 2014).

Viral pathogens can adversely impact cowpea productivity; some of these have been linked in some cases to cowpea losses of up to 100% (Nsa and Kareem, 2015). Their destructive mechanisms that negatively affect cowpea include the reduction they cause in the population/growth and development of Rhizobium, thereby reducing the necessary root nodulation in cowpea (Taiwo et al., 2014). Up to 40 viruses adversely affect cowpea yields globally. Some of the most devastating viral pathogens of cowpea are the cowpea aphid-borne mosaic virus (CABMV), cowpea wild mottle virus (CPMMV), and CPSMV (Boukar et al., 2013; Odedara and Kumar, 2017).

Parasitic weeds cause serious losses in cowpea production/yields (Li and Timko, 2009; Horn et al., 2015; Omoigui et al., 2017). Eliminating these weeds in the course of cowpea production is difficult because they could be dormant in the soil for upward of 20years (Kamara et al., 2014). The major parasitic weeds that adversely affect the enhancement of cowpea production in Africa are Striga gesnerioides and Alectra vogelii (Figure 1).

Genomics is the foremost pioneer omics that is presented as an advanced biotechnological technique and that uses genes and the genome transformation of plants and microbes for molecular breeding in order to establish improved crop cultivars. Genomics techniques are fast and precise, and can be selectively used to highlight the functional genes of desired traits for the improvement of a plant. Specifically, genomics techniques can be applied in the modification of genes in that they add genes to a plant, or by using RNAi, they knock down genes from a plant, in so doing, accomplish phenotypic traits of interest faster than the conventional plant-breeding method does. In the quest to enhance cowpea productivity, genomics-based smart biotechnology techniques have been deployed to breed improved cowpea cultivars. In such cases, the focus is on looking at the whole genome in terms of genotypic diversity and fingerprinting for cultivar improvement traits (Xu et al., 2017; Wu et al., 2018; Seo et al., 2020).

Molecular-based approach has been deployed towards improving cowpea cultivars using molecular markers and genomic-breeding techniques. An authenticated cowpea genetic resource is the foundation for efficient breeding and conservation. Genotypic diversity assessment is done by using both phenotypic and molecular traits characterization.

Research efforts at genetic breeding of cowpea cultivars using these DNA markers have been investigated by Kolade et al. (2016); Chen et al. (2017a).

SNPs are the preferred markers in genotypic assessment studies due to their wide distribution in the genome and they are highly efficient (Nkhoma et al., 2020).

Following advancement in plants genome resources, molecular markers are now widely deployed in genetic variability assessment, molecular breeding, and DNA fingerprinting (Su et al., 2018).

Among the genomic-breeding research effort, the Illumina Cowpea iSelect Consortium Array (Muñoz-Amatriaín et al., 2017) was an important landmark. This great research effort led to the development of a minicore (referred to as the “UCR Minicore”) which composed of 368 domesticated cowpeas selected from a larger set of _5000 accessions comprising the UC Riverside cowpea collection.

This array contained 51,128 SNPs derived from whole genome sequences (WGS) of 37 diverse cowpea accessions. Single nucleotide polymorphism (SNPs) is distributed uniformly in cowpea genome and indicates variation in genes of cowpea. Thus, they provide an ideal resource for cowpea molecular breeding and new variety protection. SNPs are vital genomics techniques for assessment of key traits in cowpea like constructing genomic linkage map, for QTL, for the detection as well as assessing germplasm genetic diversity (Paudel et al., 2021).

Also, the majority of the international institute of tropical agriculture (IITA) minicore collection (298 accessions) was genotyped using genotypic base sequencing (GBS) with 2,276 SNPs, this identified three major subpopulations (Fatokun et al., 2018), but showed dispersion of West and Central African accessions across the three subpopulations.

Another giant stride in the progress of cowpea genomics study was achieved by using next generation sequencing advancement (Lonardi et al., 2019) to authenticate the whole genome of an improved cowpea genotypes, thus providing a key resource that is crucial to deciphering the morpho-physiological response of cowpeas.

Building on this developments and report of full SNP data release for the UCR Minicore, numerous follow up studies has been investigated for more focus cowpea research, that include studies on pattern of seed coat (Herniter et al., 2019), color of seed coat (Herniter et al., 2018), size of seeds (Lo et al., 2019), resistance to bruchid infestation (Miesho et al., 2019), plant herbivore resistance (Steinbrenner et al., 2020) and pod shattering (Lo et al., 2021).

With better comprehension of genomic basis of variation, genome-wide association studies (GWAS) studies have been highlighted in cowpea for pod length (Xu et al., 2017), root architecture (Burridge et al., 2017), cowpea plant improvement traits, as well as the flowering period (Muñoz-Amatriaín et al., 2021). All these findings are appreciated because cowpea genetic diversity assessment is necessary for strengthening breeding programs in order to develop high yielding dual-purpose cultivars with good grain and fodder yields.

Transcriptomics is a vital biotechnological technique that makes for a comprehensive understanding of genomics functionality (Valdés et al., 2013). Transcriptomics regulates the expression of genes in the context of biotic and abiotic stresses. Transcriptomics is a dynamic technique that expresses genes at any given time and under different circumstances.

With the advancement of functional genomics, the identification of novel genes having vital functions in plant growth/development and adaptation to stressful conditions have been characterized for crop cultivars (Zhang et al., 2017). Also, RNA expression profiling is important in understanding plant functionality.

Transcriptomics as a part of multi-omics biotechnological techniques have led to the detection of novel genes useful in response to both biotic and abiotic stresses in plants.

Transcriptomics approaches utilizes high-throughput sequencing platforms to generate enormous useful transcript data through techniques such as RNA sequencing, microarray and serial analysis of gene expression (SAGE) to elucidate non-coding and coding RNAs expression profiles to plant biotic and abiotic stresses (Cramer et al., 2011; Santos et al., 2018).

Several factors like the duration and extent of stress conditions, determines the adaptability and tolerance of a plant to stresses. However, experimental design, handling of tissue samples, isolation of RNA and stability of RNA also play major role in any transcriptomic analysis (Gokce et al., 2020).

The characterization of different parts of the cowpea plant through transcriptomics has been carried out in studies that express the diverse genes essential for cowpea growth and development. The stress-resilient genes have also been characterized and their role in the overall improvement of cowpea has also been highlighted (Yao et al., 2016; Chen et al., 2017b; Amorim et al., 2018; Spriggs et al., 2018).

Proteins are a vital constituent of plants. Large quantities of protein are responsible for the key functional roles that plants perform. As a smart biotechnological technique, proteomics entails the expression of functional characteristics, structural features, and the translation/manifestation of beneficial traits in plants. Another important attribute of the proteomics technique is that it can be used to better elucidate a pesticide’s mode of action, its mechanisms, and its biodegradation. The outputs/benefits that can be derived by applying proteomics include the authenticity of the food product, the assurance of food security that it represents and the sustainability of energy that the food product offers to consumer, as well as the maintenance of an environmental balance (Agrawal et al., 2012; Landim et al., 2017).

Proteomics as a key branch of “omics” technology aims at investigating protein’s structure, function, as well as their interactions with other proteins and other components, including the modifications arising from these interactions through the use of analytical techniques.

Proteomics approach involves analysis and the elucidation of functional expression of proteins in order to understand biological processes (Iwamoto and Shimada, 2018; Chen and Weckwerth, 2020).

Proteins are vital components of all biological process. To fully comprehend the response of plants to biotic and abiotic stresses, proteomics studies must be assessed, along with other multi-omics technology (Gokce et al., 2020). Changes in gene expression influences appropriate response in protein composition/abundance and affect cellular functions.

Proteomics studies are assessed using spectroscopic method usually by mass spectroscopy (MS)-based technology. This is done by MALDI-TOF MS or with liquid chromatography mass spectrometry (LC–MS) techniques. Proteomics studies have led to the characterization of different stress response proteins in planted crops under stress conditions (Rathi et al., 2016; Kosová et al., 2018; Matamoros and Becana, 2021).

Metabolomics is an advanced and powerful smart biotechnique that identifies functionally active metabolites, their roles, and the diverse biochemical processes that the metabolites play in plant genotypes and phenotypic expressions (Führs et al., 2009; Aliferis and Chrysayi-Tokousbalides, 2011). Metabolomics tools can be deployed in identifying and monitoring physiological responses in plants and the metabolic pathways or linkages arising from the biotic and abiotic stress exerted upon plants. In fact, these tools are able to enhance crop development and improve plant health (Dixon et al., 2006; Goufo et al., 2017).

In a study on drought response of three cowpea landraces using leaf physiological and metabolites profiling assessment, (Gomes et al., 2020), used gas chromatography time of flight mass spectrometry (GC-TOF-MS) and reported that cowpea landrace A116 genotype drought response was best with the accumulation of 14 bioactive metabolites that included proline, valine, and rhamnose and raffinose, isoleucine, fucose, urea, alanine, sucrose, and putrescine.

Also, in a study on metabolites (polyphenols and carotenoids) in V. unguiculata sprouts by Yeo et al. (2018), investigated using high-performance liquid chromatography (HPLC), electrospray ionization-mass spectrometry (ESI-MS), gas chromatography–mass spectrometry (GC–MS), and gas chromatography, 39 hydrophilic compounds were identified and quantitated. Thus, the study provides a new approach for enhancing the carotenoid and phenylpropanoid production of V. unguiculata.

Metabolomics as a powerful omics-based approach can be applied as a tool to explore different aspects in plant breeding, the regulatory mechanisms related to plant growth and development (including those related to crop productivity and performance), adaptation to biotic and abiotic stresses, nutritional improvement, and selection of cultivars for agriculture. Metabolomes are simply metabolites (both secondary and primary) having low molecular weight (usually <1,500Da), including their precursors and intermediates of the corresponding biosynthetic pathways. Such compounds are considered the end products of gene expression and protein activity, modulating processes between the genome and environment and indicating the functional status of the organism. Moreover, they are an indispensable part of the plant metabolism, influencing all biological processes, such as plant biomass and architecture, and those involved in plant defense or adaptation to biotic and abiotic stresses (Sharma et al., 2021).

In a comprehensive study on cowpea osmoregulation response under drought stress, (Goufo et al., 2017) investigated and provided a detailed metabolic profile of a broad range of primary and secondary metabolites in cowpea, including elemental solutes using (leaves and roots). Their findings revealed that the mechanisms deploy in modifying cowpea metabolism response to water deficit is through interplay between the shikimate and arginine/proline pathways, leading to three drought-responsive metabolites, namely galactinol, proline, and quercetin 3-O-6''-malonylglycoside.

In a study aimed at identifying metabolic responses and key factors associated with Mn tolerance using Mn-tolerant and Mn-sensitive genotypic cultivars; (Führs et al., 2012) reported that manganese tolerance is a consequence of genotypic/constitutive higher concentrations of metabolites detoxifying manganese and reactive oxygen species.