Abstract
Asparagus bean (Vigna unguiculata ssp. sesquipedalis) is the Asian subspecies of cowpea, a drought-resistant legume crop native to Africa. In order to explore the genetic variation of drought responses in asparagus bean, we conducted multi-year phenotyping of drought resistance traits across the Chinese asparagus bean mini-core. The phenotypic distribution indicated that the ssp. sesquipedalis subgene pool has maintained high natural variation in drought responses despite known domestic bottleneck. Thirty-nine SNP loci were found to show an association with drought resistance via a genome-wide association study (GWAS). Whole-plant water relations were compared among four genotypes by lysimetric assay. Apparent genotypic differences in transpiration patterns and the critical soil water threshold in relation to dehydration avoidance were observed, indicating a delicate adaptive mechanism for each genotype to its own climate. Microarray gene expression analyses revealed that known drought resistance pathways such as the ABA and phosphate lipid signaling pathways are conserved between different genotypes, while differential regulation of certain aquaporin genes and hormonal genes may be important for the genotypic differences. Our results suggest that divergent sensitivity to soil water content is an important mechanism configuring the genotypic specific responses to water deficit. The SNP markers identified provide useful resources for marker-assisted breeding.
Highlights
Cowpea (Vigna unguiculata) is an important grain, vegetable, and fodder legume crop around the world
Using previous genome-wide SNPs data for the population (Xu et al, 2012), a genome-wide association study (GWAS) was performed under both a generalized-linear model (GLM) and mixed-linear model (MLM) to search for SNP loci associated with the three traits
Like the better-characterized drought-resistant crop species chickpea (Zaman-Allah et al, 2011) and pearl millet (Kholová et al, 2010), dehydration avoidance has been suggested to be the primary mechanism for achieving drought resistance in African cowpea (Bates and Hall, 1982; Likoswe and Lawn, 2008)
Summary
Cowpea (Vigna unguiculata) is an important grain, vegetable, and fodder legume crop around the world. Drought responses in asparagus beans outperforming groundnut, sorghum and pearl millet (Pennisetum americanum) under severe soil drought conditions (Ewansiha and Singh, 2006). Both the capacity of cowpea plants to withstand water deficits and their stress reactions vary significantly by genotype (Watanabe et al, 1997; Muchero et al, 2008). Geneticists have developed simple but reliable protocols to assess the levels of drought resistance at a large scale, such as visual scoring of drought-induced premature senescence, wilt, loss of stem greenness, and scoring of grain yield components (Muchero et al, 2008; Agbicodo et al, 2009). Large gaps currently exist among the various types of knowledge
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