Evaluation and QTL Mapping of Salt Tolerance in Yardlong Bean [Vigna unguiculata (L.) Walp. Subsp. unguiculata Sesquipedalis Group] Seedlings

Abstract

Salinity is a major abiotic stress that limits productivity in yardlong bean. Identification of the quantitative trait loci (QTL) underlying salt tolerance is a prerequisite for successful marker-assisted selection when breeding for salt-tolerance. The objective of this study was to use a set of insertions and deletions (InDels) found in salt stress-responsive genes to construct a linkage map and identify reliable markers that can guide breeding efforts for novel, high-yield, salt-tolerant varieties of yardlong bean (Vigna unguiculata). A linkage map was constructed from 103 InDel markers in an F2 population consisting of 143 plants produced by crossing yardlong bean varieties Suzi 41 (salt tolerant) and Sujiang 1419 (salt sensitive). The markers were clustered across 9 chromosomes spanning 975.7 cM in total length, with an average distance between adjacent markers of 9.5 cM. Using this linkage map, we identified six major QTLs associated with control of salt tolerance-related traits on chromosomes (Chr.) 08, 09, and 11, which explained 9.9% ~ 72.7% of the phenotypic variation. Four major QTLs showed co-location in the region between VUIn584 and VUIn724 on Chr.09, associated with the traits of salt tolerance rating (STR), leaf chlorophyll content (SPAD), aerial biomass fresh weight (AFW), and root fresh weight (RFW). These QTLs provide a valuable reference for marker-assisted breeding, QTL fine mapping, and the cloning and characterization of salt-tolerance candidate genes.