Breeding of Vegetable Cowpea for Nutrition and Climate Resilience in Sub-Saharan Africa: Progress, Opportunities, and Challenges

Genome-Wide Identification and Characterization of Major RNAi Genes Highlighting Their Associated Factors in Cowpea (Vigna unguiculata (L.) Walp.)

In different regions of the world, cowpea (Vigna unguiculata (L.) Walp.) is an important vegetable and an excellent source of protein. It lessens the malnutrition of the underprivileged in developing nations and has some positive effects on health, such as a reduction in the prevalence of cancer and cardiovascular disease. However, occasionally, certain biotic and abiotic stresses caused a sharp fall in cowpea yield. Major RNA interference (RNAi) genes like Dicer-like (DCL), Argonaute (AGO), and RNA-dependent RNA polymerase (RDR) are essential for the synthesis of their associated factors like domain, small RNAs (sRNAs), transcription factors, micro-RNAs, and cis-acting factors that shield plants from biotic and abiotic stresses. In this study, applying BLASTP search and phylogenetic tree analysis with reference to the Arabidopsis RNAi (AtRNAi) genes, we discovered 28 VuRNAi genes, including 7 VuDCL, 14 VuAGO, and 7 VuRDR genes in cowpea. We looked at the domains, motifs, gene structures, chromosomal locations, subcellular locations, gene ontology (GO) terms, and regulatory factors (transcription factors, micro-RNAs, and cis-acting elements (CAEs)) to characterize the VuRNAi genes and proteins in cowpea in response to stresses. Predicted VuDCL1, VuDCL2(a, b), VuAGO7, VuAGO10, and VuRDR6 genes might have an impact on cowpea growth, development of the vegetative and flowering stages, and antiviral defense. The VuRNAi gene regulatory features miR395 and miR396 might contribute to grain quality improvement, immunity boosting, and pathogen infection resistance under salinity and drought conditions. Predicted CAEs from the VuRNAi genes might play a role in plant growth and development, improving grain quality and production and protecting plants from biotic and abiotic stresses. Therefore, our study provides crucial information about the functional roles of VuRNAi genes and their associated components, which would aid in the development of future cowpeas that are more resilient to biotic and abiotic stress. The manuscript is available as a preprint at this link: doi:10.1101/2023.02.15.528631v1.

Vigna unguiculata L. Walp. Leaves as a Source of Phytochemicals of Dietary Interest: Optimization of Ultrasound-Assisted Extraction and Assessment of Traditional Consumer Habits

Vigna unguiculata L. Walp. is an African crop spread worldwide mainly for pulses production. Despite being a neglected and under-utilized food, cowpea leaves are a rich source of phytochemicals and micronutrients. The aim of the work is to characterize the phytochemical composition of cowpea leaves by an optimized ultrasound-assisted extraction (USAE) and to compare raw and boiled leaves. A three-level factorial design (Box-Behnken) was employed for the optimization of the USAE considering three different parameters (% ethanol, drug-to-solvent ratio, and number of cycles). The optimized extracts were characterized by LC/MS/MS. Finally, leaves were boiled at 100 °C for 30 min to simulate traditional cooking procedures and compared to raw leaves. The best extraction condition was EtOH/H2 O 1 : 2 v/v, drug to solvent ratio 1 : 47 w/v, and 3 extraction cycles. The phytochemicals identified mainly belong to the family of phenolic acids, flavonoids, terpenoids, and alkaloids. Boiled leaves revealed a significant loss of most phytochemicals and a net decrease of their antioxidant activity compared to the raw ones. The results highlight the potential nutraceutical value of cowpea leaves whilst the impoverishment triggered by traditional consumer habits pushes the need to evaluate alternative cooking procedures helpful in the maintenance of their phytochemical properties.

Evaluation of the Physical, Chemical, Technological, and Sensorial Properties of Extrudates and Cookies from Composite Sorghum and Cowpea Flours

In recent years, there has been a growing demand for gluten-free and functional products, driven by consumer preferences for healthier and more diverse food choices. Therefore, there is a need to explore new ingredients that can be used as alternatives to traditional gluten-containing grains. Thus, this work evaluated the physical, chemical, technological, and sensorial properties of extrudates and cookies from composite tannin sorghum (rich in resistant starch) and white cowpea flours. Extrudates and cookies were produced from a composite flour made of sorghum and cowpea, at a sorghum:cowpea flour ratio of 70:30, 50:50, and 30:70. Then, raw flours, cookies, and extrudates were characterized (dietary fiber, resistant starch, proteins, antioxidant capacity, pasting properties, etc.). Results obtained for particle size distribution and bulk density indicated that the particles increased and the color changed with the addition of cowpea flour. The raw tannin sorghum flour had a higher resistant starch concentration (36.3%) and antioxidant capacity (211.2 µmolTE/g), whereas cowpea flour had higher levels of proteins (18.7%) and dietary fiber (20.1%). This difference in the raw flour composition contributed to the nutritional value of the extrudates and cookies, especially the cookies which undergo dry heat and had higher retention of resistant starch and antioxidants. Moreover, sorghum flour presented a higher tendency to retrograde (high setback), which was decreased by the addition of cowpea flour. Overall acceptance and intention to purchase were higher for extrudates with 100% sorghum flour (6.52 and 68.3%, respectively) and cookies with 70% cowpea flour (7.03 and 76.7%, respectively). Therefore, nutritious and functional gluten-free extrudates and cookies, of good acceptability, can be produced from composite tannin sorghum and white cowpea flours.

Unlocking Cowpea's Defense Responses: Conserved Transcriptional Signatures in the Battle against CABMV and CPSMV Viruses

Cowpea aphid-borne mosaic virus (CABMV) and Cowpea severe mosaic virus (CPSMV) threaten cowpea commercial production. This study aimed to analyze Conserved Transcriptional Signatures (CTS) in cowpea's genotypes that are resistant to these viruses. CTS covered up- (UR) or down-regulated (DR) cowpea transcripts in response to CABMV and CPSMV mechanical inoculations. The conservation of cowpea's UR defense response was primarily observed with the one hpi treatments, with decreased CTS representatives as time elapsed. This suggests that cowpea utilizes generic mechanisms during its early interaction with the studied viruses, and subsequently employs more specialized strategies for each viral agent. The potential action of the CTS-UR emphasizes the importance of redox balance, ethylene and jasmonic acid pathways. Additionally, the CTS-UR provides evidence for the involvement of R genes, PR proteins, and PRRs receptors-extensively investigated in combating bacterial and fungal pathogens-in the defense against viral inoculation. AP2-ERF, WRKY, and MYB transcription factors, as well as PIP aquaporins and MAPK cascades, also emerged as significant molecular players. The presented work represents the first study investigating conserved mechanisms in the cowpea defense response to viral inoculations, highlighting relevant processes for initial defense responses.

A Genome-Wide Association Study Reveals Region Associated with Seed Protein Content in Cowpea

Cowpea (Vigna unguiculata L. Walp., 2n = 2x = 22) is a protein-rich crop that complements staple cereals for humans and serves as fodder for livestock. It is widely grown in Africa and other developing countries as the primary source of protein in the diet; therefore, it is necessary to identify the protein-related loci to improve cowpea breeding. In the current study, we conducted a genome-wide association study (GWAS) on 161 cowpea accessions (151 USDA germplasm plus 10 Arkansas breeding lines) with a wide range of seed protein contents (21.8~28.9%) with 110,155 high-quality whole-genome single-nucleotide polymorphisms (SNPs) to identify markers associated with protein content, then performed genomic prediction (GP) for future breeding. A total of seven significant SNP markers were identified using five GWAS models (single-marker regression (SMR), the general linear model (GLM), Mixed Linear Model (MLM), Fixed and Random Model Circulating Probability Unification (FarmCPU), and Bayesian-information and Linkage-disequilibrium Iteratively Nested Keyway (BLINK), which are located at the same locus on chromosome 8 for seed protein content. This locus was associated with the gene Vigun08g039200, which was annotated as the protein of the thioredoxin superfamily, playing a critical function for protein content increase and nutritional quality improvement. In this study, a genomic prediction (GP) approach was employed to assess the accuracy of predicting seed protein content in cowpea. The GP was conducted using cross-prediction with five models, namely ridge regression best linear unbiased prediction (rrBLUP), Bayesian ridge regression (BRR), Bayesian A (BA), Bayesian B (BB), and Bayesian least absolute shrinkage and selection operator (BL), applied to seven random whole genome marker sets with different densities (10 k, 5 k, 2 k, 1 k, 500, 200, and 7), as well as significant markers identified through GWAS. The accuracies of the GP varied between 42.9% and 52.1% across the seven SNPs considered, depending on the model used. These findings not only have the potential to expedite the breeding cycle through early prediction of individual performance prior to phenotyping, but also offer practical implications for cowpea breeding programs striving to enhance seed protein content and nutritional quality.

Research progress and applications of colorful Brassica crops

MAIN CONCLUSION

We review the application and the molecular regulation of anthocyanins in colorful Brassica crops, the creation of new germplasm resources, and the development and utilization of colorful Brassica crops. Brassica crops are widely cultivated: these include oilseed crops, such as rapeseed, mustards, and root, leaf, and stem vegetable types, such as turnips, cabbages, broccoli, and cauliflowers. Colorful variants exist of these crop species, and asides from increased aesthetic appeal, these may also offer advantages in terms of nutritional content and improved stress resistances. This review provides a comprehensive overview of pigmentation in Brassica as a reference for the selection and breeding of new colorful Brassica varieties for multiple end uses. We summarize the function and molecular regulation of anthocyanins in Brassica crops, the creation of new colorful germplasm resources via different breeding methods, and the development and multifunctional utilization of colorful Brassica crop types.

Cowpea Constraints and Breeding in Europe

Cowpea (Vigna unguiculata (L.) Walp.) is a legume with a constant rate of cultivation in Southern European countries. Consumer demand for cowpea worldwide is rising due to its nutritional content, while Europe is constantly attempting to reduce the deficit in the production of pulses and invest in new, healthy food market products. Although the climatic conditions that prevail in Europe are not so harsh in terms of heat and drought as in the tropical climates where cowpea is mainly cultivated, cowpea confronts with a plethora of abiotic and biotic stresses and yield-limiting factors in Southern European countries. In this paper, we summarize the main constraints for cowpea cultivation in Europe and the breeding methods that have been or can be used. A special mention is made of the availability plant genetic resources (PGRs) and their potential for breeding purposes, aiming to promote more sustainable cropping systems as climatic shifts become more frequent and fiercer, and environmental degradation expands worldwide.

Breeding implications of nodulation performance and root structure under natural inoculation for soil fertility enhancement and sustainable cowpea production

Nitrogen deficiency is the most limiting abiotic stress factor affecting the grain yield of cowpea (Vigna unguiculata L.) in sub-Saharan Africa (SSA) countries. Breeding for high-yielding potential in association with high nitrogen fixation performance is the principal objective of cowpea breeding programs to improve both the productivity and production of this orphan crop in the region. Therefore, the present study was undertaken to determine the diversity of genotypes for nodulation capacity in two environments and to understand the root architecture and morphology of genotypes as well as grain yield and yield-related traits in 324 cowpea genotypes. The experiment was conducted in two different environments during the 2017 cropping season. The experiments were laid out in 18 × 18 simple lattice design. Grain yield exhibited highly significant and positive genotypic correlations with stem diameter, basal root length of 1st whorls, basal root branching density, taproot length and adventitious root length, demonstrating that selection of cowpea genotypes based on these traits could be effective to capitalize on grain yield under low nitrogen conditions. Days to flowering, days to maturity, stem diameter, 1st whorl angle, basal root length of 1st whorls, basal root branching density, taproot length, adventitious root diameter and adventitious root length had significant and positive genotypic correlations with days to maturity. The first ten principal components (PC) explained 65.13% of the total variation. Stem diameter, taproot width, and taproot length traits were important contributors to the variability in the first PC. The highest inter-cluster distance (D2) was recorded between clusters III and IV. However, clusters II and V recorded the minimum inter-cluster distance (78.96 units). The range of intra-cluster distance was 24.22–5,112.92 units, indicating that the high genetic distance displayed within and between clusters has to be exploited via crossing and selecting the most divergent parents for future cowpea improvement. Five clusters of cowpea genotypes were evident, and within the clusters, the genotypes had good nodulation potential with high grain yield traits, which could significantly contribute to SSA food and nutritional security. Moreover, it can contribute to resilience and improve crop production and sustainability under marginal environmental conditions.