Genetic mapping and localization of major QTL for bitterness in melon (Cucumis melo L.)

Melon (Cucumis melo L., 2n=2x=24) is a eudicot diploid plant species belongs to the Cucurbitaceae family, which is famous for its specific biological properties and economic importance. Melon with high cucurbitacin contents taste unpleasant and are not preferred by consumers, but the underlying molecular mechanism for the bitterness related trait is not fully known. Therefore, the study of bitterness in melon has important practical value. Exploring the genetic rules of bitterness related traits and the key genes in the process of biosynthesis and metabolic regulation, as well as developing the molecular markers related to the bitterness of melon can provide guidance for the selection of non-bitter taste melon varieties and furnish reference for related studies of cucurbitacin. Here, we constructed a genetic linkage map using type IIB endonucleases restriction-site associated DNA (2b-RAD) based high throughput SNP genotyping data of a BC1 mapping family. The total length of the linkage map was 851.53 cM, with an average distance of 1.11 cM between adjacent markers. Genetic analysis of F-2 and BC1 populations derived from two parental lines (C68 with non-bitter taste and C69 with bitter taste) revealed that the melon bitterness related trait is controlled by dual locus, and bitterness is dominant to non-bitterness. QTL mapping identified 3 significant QTLs in 2 linkage groups (LGs). Then, based on the InDel markers obtained from deep re-sequencing of the two parents, we verified the accuracy of the mapping interval. Especially, the Polymerase Chain Reaction (PCR) based co-separation markers on chromosome 2 and chromosome 5 revealed that the genotypes perfectly matched with the phenotypes in F2 and XC6 population, which further proves the accuracy of our mapping results for melon bitterness. Our present study will provide fine mapping of melon bitterness related trait and facilitate marker-assisted selection for the development of non-bitterness cultivars.