GBS-based map construction and QTL identification for major agronomic traits in mungbean

Abstract

Mungbean is an important crop grown in South, East and Southeast Asia. As mungbean contains a high protein content, along with other nutritional befinits such as carboyhoydrates, lipids, minerals, and vitamins, it is important to investigate genomics regions controlling specific agronomic traits for the improvement in breeding programs, where most of the major traits are quantitatively inherited. The general objective is to identify quantitative trait loci (QTLs) of mungbean associated with days to first flowering (DFF), days to 50% flowering (DF), 100-seed weight (100-SW), lodging resistance (Ldge), and cercospora leaf spot resistance (CLS). Flowering is one of the most crucial trait to be studied in mungbean because of its direct correlation with crop yield. It has previously been reported that a higher number of pod yield produces after the two to three weeks of first flowering and its consequences of a high yielding mungbean. Therefore, it is of great interest to investigate the genetic loci underlying flowering time and its associated traits, allowing breeders to develop novel varieties with efficient altered flowering times. In this study, a total of 190 F6 recombinant inbred lines (RILs) developed from the cross of VC 1973A (Sunhwa nokdu) and VC 2984 (Gyeonggi Jaerae #5) were used to identify quantitative trait loci (QTLs) for DFF, DF, 100-SW, Ldge, CLS, plant height (PH), and number of branches (NB). A genetic map was constructed using 798 single nucleotide polymorphism (SNP) markers developed by a genotyping-by-sequencing (GBS) method from a segregating a RIL population. The generated markers were distributed over all 11 chromosomes (Chrs), covering 757.39 centiMorgans (cM) of mungbean genome with the average distance between adjacent markers of 0.95 cM. Using composite interval mapping (CIM), we identified six QTLs were identified for DFF and DF, four for 100-SW, two for PH, two for NB, one for Ldge, and two for CLS. Among them, one QTL located on Chr4 was identified to be associated with three agronomics traits with significant LOD scores, of which they were DFF, DF and PH. This genomic region then was deployed in the soybean genome for comparative analysis to identify synteny relationships between mungbean and soybean, whether this region co-localized with the soybean flowering QTL regions.