Cowpea [ Vigna unguiculata (L.) Walp] is a globally important food security crop. However, it is susceptible to pest and disease; hence, constant breeding efforts based on its diversity are required for its improvement. The present study aims to investigate the genetic diversity, population structure, and linkage disequilibrium (LD) among 274 cowpea accessions from different origins. A total of 3,127 single nucleotide polymorphism (SNP) markers generated using diversity array technology (DArT) was used. Population structure, neighbor‐joining clustering, and principal component analyses indicated three subpopulations within the germplasm. Results of STRUCTURE analysis and discriminant analysis of principal components (DAPC) were complementary in assessing the structuration of the diversity among the germplasm, with the grouping of the accessions improved in DAPC. Genetic distances of 0.005–0.44 were observed among accessions. Accessions from western and central Africa, eastern and central Africa, and Asia were predominant and distributed across all subpopulations. The subpopulations had fixation indexes of 0.48–0.56. Analysis of molecular variance revealed that within subpopulation variation accounted for 81% of observed genetic variation in the germplasm. The subpopulations mainly consisted of inbred lines (inbreeding coefficient = 1) with common alleles, although they were from different geographical regions. This reflects considerable seed movement and germplasm exchange between regions. The LD was characterized by low decay for great physical distances between markers. The LD decay distance varied among chromosomes with the average distance of 80–100 kb across the genome. Thus, crop improvement is possible, and the LD will facilitate genome‐wide association studies on quality attributes and critical agronomic traits in cowpea.

Understanding factors influencing the expression of a trait is key in designing a breeding program. Genotype by environment interaction has great influence on most quantitative traits. Promiscuous nodulation is a trait of importance for soybean production in Africa, because of the soil bacteria Bradyrhizobium japonicum not being indigenous in most African soils. Most soybean cultivars require B. japonicum for nodulation leading to the need for seed inoculation before sowing soybean in Africa. Few cultivars have capability to nodulate with Bradyrhizobia spp. that are different from B. japonicum and native in African soils. Such cultivars are termed “promiscuous cultivars.” Field experiments were conducted in six locations in Uganda for two seasons, to investigate the extent of environmental influences on the nodulation ability of promiscuous soybean genotypes. Additive main effect and multiplicative interaction effects showed highly significant environment and genotype by environment (G × E) interaction effects on all nodulation traits. G × E interaction contributed more to the total variation than genotypes. The genotypes Kabanyolo I and WonderSoya were the most stable for nodules’ dry weight (NDW), which is the nodulation trait the most correlated with grain yield. Genotype UG5 was the most stable for nodules’ number (NN), and Nam II for nodules’ effectiveness (NE). The genotype NamSoy 4M had the highest performance for NN, NFW, and NDW, but was less stable. WonderSoya had the highest NE. Genotype and genotype by environment analysis grouped environments into mega-environments (MEs), and four MEs were observed for NDW, with NamSoy 4M the winning genotype in the largest ME, and Kasese B the ideal environment for that nodulation trait. This study provides information that can guide breeding strategies. The low genetic effect that led to high environmental and G × E interaction effects raised the need for multi-environments testing before cultivar selection and recommendation. The study revealed genotypes that are stable and others that are high performing for nodulation traits, and which can be used as parental lines in breeding programs.

Cowpea (Vigna unguiculata (L.) Walp) is a highly nutritious grain legume crop in the world. However, cowpea production is constrained by legume pod borer (Maruca vitrata Fabricius) (LPB), which feeds on various parts of cowpea plant, causing a complete crop failure. An analysis of the existing literature revealed LPB as a serious threat to cowpea production worldwide, with a more noticeable damage in Africa. Attempts to develop and use LPB-resistant cowpea varieties have not shown significant results because of challenges, such as interspecific crossing barriers, genetic variability among LPB strains, effects of genotype-by-environment interaction, limited knowledge of the genetic architecture of the trait, and the socio-political barriers to the adoption of transgenic cowpea varieties in some countries. Combining multi-environment trials with precise phenotyping would help optimize selection of best-performing cowpea genotypes to reduce LPB infestation. Many molecular tools (e.g., markers systems, genetics maps, high-throughput genotyping, and quantitative trait loci (QTL) analysis) are available to support breeding for LPB resistance in cowpea. In addition, mutation breeding, tissue culture, reverse genetics, clustered regularly interspaced short palindromic repeats (CRISPR) technologies can be used to increase genetic variability in cowpea for LPB resistance. The effective use of these technologies relies on an enabling legal and socio-economic-political environment for fast development and adoption of LPB-resistant cowpea varieties.