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.

中文翻译：

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豇豆种质的多样性、种群结构和连锁不平衡

豇豆 [豇豆(L.) Walp] 是一种全球重要的粮食安全作物。但是，它容易受到病虫害的侵袭；因此，需要基于其多样性的不断育种努力来改进其。本研究旨在调查来自不同来源的 274 个豇豆种质之间的遗传多样性、种群结构和连锁不平衡 (LD)。使用了使用多样性阵列技术 (DArT) 生成的总共 3,127 个单核苷酸多态性 (SNP) 标记。种群结构、邻接聚类和主成分分析表明种质内有三个亚群。结构分析和主成分判别分析（DAPC）的结果在评估种质多样性的结构方面是互补的，在DAPC中改进了种质的分组。在种质中观察到遗传距离为 0.005-0.44。来自西部和中部非洲、东部和中部非洲以及亚洲的种质占主导地位，并分布在所有亚群中。亚群的固定指数为 0.48-0.56。分子方差分析表明，亚群内变异占种质中观察到的遗传变异的81%。亚群主要由具有共同等位基因的近交系（近交系数= 1）组成，尽管它们来自不同的地理区域。这反映了区域之间相当大的种子移动和种质交换。LD 的特点是标记之间的物理距离大，衰减低。染色体之间的 LD 衰减距离不同，整个基因组的平均距离为 80-100 kb。因此，