Cowpea (V. unguiculata L. Walp.) is an important grain legume, fodder and vegetable crop in many tropical and subtropical regions of the world [1, 2]. Asparagus bean (V. unguiculata ssp. sesquipedialis), also known as ‘yard long’ bean or snap bean is a subspecies and distinctively domesticated type of cowpea grown mainly for vegetable use in many Asian countries. Asparagus bean, together with the African cowpea (V. unguiculata ssp. unguiculata), forms the two main divisions of cultivated cowpea . Due to selection towards traits favorable for vegetable use, the present day asparagus bean differs a lot from African cowpea in many aspects including plant architecture (climbing versus erect), growth habit (indeterminate versus determinate), pod length and pod fiber content [4, 5].
Recent progress in cowpea genomics has provided an opportunity to unravel the genetic basis of horticulturally important traits in asparagus bean. Bead-assay SNP genotyping was recently used to build a consensus genetic map which includes more than 1,000 loci from as many as thirteen different RIL populations [6, 7]. Among the 13 mapping populations, one is derived from an inter-varietal asparagus bean cross. This population has also been used to develop a separate, but comparable, genetic linkage map of asparagus bean by integrating many SSR markers . This subspecies/population-specific map has been especially useful in mapping two qualitative traits, namely, flower and seed coat color in the authors’ lab .
For commercial asparagus bean production, tender and crisp immature pods during early development is desired. This can be, at least in part, accomplished by breeding early-flowering varieties with the potential to yield more pods per plant. Early flowering is known to be related to node position at which first inflorescence occurs; therefore, the node to first flower has been practically used as an indirect indicator of earliness . Another desirable trait of asparagus bean is extended longevity or delayed plant senescence. This characteristic usually allows for two or more flushes of flowering, potentially resulting in more pods per plant. The aforementioned traits including days to first flowering (FLD), nodes to first flower (NFF), leaf senescence (LS) and pod number per plant (PN) are among the most horticulturally important traits in asparagus bean. All four traits are inherited quantitatively based on their field behaviors, and as such, dissecting their genetic basis calls for adequate statistical methods such as bi-parental QTL mapping.
Thus far, QTL mapping has not been reported in asparagus bean × asparagus bean populations; however, chromosome regions associated with horticultural/domestication-related traits have been mapped using cowpea populations of ssp. unguiculata pedigree. QTLs for 24 domestication-related traits were mapped using two temporal segregation populations derived from an asparagus bean × wild cowpea cross . QTLs for seed weight and pod shattering were mapped using a normal cowpea × wild cowpea RIL population . Earlier works include those which focused on a wide range of horticultural traits including organ sizes, yield components, plant height etc. [13–15]. Unfortunately these works remained anchored to the marker technology in which they were discovered. Here we present the identification of QTLs for four horticulturally important traits using an asparagus bean intervarietal RIL population. Two of these traits i.e. FLD and PN have been investigated previously using different plant materials  while the other two (LS and NFF) have been not. Many of the marker-trait associations we report are accessible via community genotypipng platforms and are useful for modern breeding, comparative genomics, and map-based cloning.