Abstract
SummaryCowpea (V. unguiculata L. Walp) is a climate resilient legume crop important for food security. Cultivated cowpea (V. unguiculata L) generally comprises the bushy, short‐podded grain cowpea dominant in Africa and the climbing, long‐podded vegetable cowpea popular in Asia. How selection has contributed to the diversification of the two types of cowpea remains largely unknown. In the current study, a novel genotyping assay for over 50 000 SNPs was employed to delineate genomic regions governing pod length. Major, minor and epistatic QTLs were identified through QTL mapping. Seventy‐two SNPs associated with pod length were detected by genome‐wide association studies (GWAS). Population stratification analysis revealed subdivision among a cowpea germplasm collection consisting of 299 accessions, which is consistent with pod length groups. Genomic scan for selective signals suggested that domestication of vegetable cowpea was accompanied by selection of multiple traits including pod length, while the further improvement process was featured by selection of pod length primarily. Pod growth kinetics assay demonstrated that more durable cell proliferation rather than cell elongation or enlargement was the main reason for longer pods. Transcriptomic analysis suggested the involvement of sugar, gibberellin and nutritional signalling in regulation of pod length. This study establishes the basis for map‐based cloning of pod length genes in cowpea and for marker‐assisted selection of this trait in breeding programmes.
Highlights
After the removal of samples showing high heterozygosity, missing data or nonparental alleles, 119 recombinant inbred lines (RILs) and all germplasm accessions were used for further analysis
After eliminating monomorphic SNPs and those with excessive number of missing and/or heterozygous calls and very low minor allele frequencies, 7988 high-quality SNPs were retained for the RIL population and 30 211 for the diversity panel
Among the RILs, pod length displayed a continuous distribution with the population means falling between the parental values (Figure 1c)
Summary
Walp., 2n = 2x = 22), native to Africa, is a worldwide important legume used as a grain, fodder or vegetable crop. Sub-Saharan Africa and Brazil are the major producers of cowpea grain, while East/South-East Asia is the main vegetable-type cowpea producer (Rachie, 1985; Timko et al, 2007). The vegetable cowpea, known as asparagus bean or ‘yardlong’ bean The asparagus bean pods can either be snapped and cooked in stew or stir-fried, or preserved with salt and chile. They provide a good source of proteins, vitamins and minerals (Timko et al, 2007). Asparagus bean is among the top ten Asian cultivated vegetables due to its high tolerance to heat and drought (National Research Council, 2006)
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