Mapping of genetic loci controlling fruit linked morphological traits of melon using developed CAPS markers

Fruit morphology traits are important commercial traits that directly affect the market value. However, studying the genetic basis of these traits in un-explored botanical groups is a fundamental objective for crop genetic improvement through marker-assisted breeding.

In this study, a quantitative trait loci (QTLs) mapping strategy was used for dissecting the genomic regions of fruit linked morphological traits by single nucleotide polymorphism (SNP) based cleaved amplified polymorphism sequence (CAPS) molecular markers. Next-generation sequencing was done for the genomic sequencing of two contrasted melon lines (climacteric and non-climacteric), which revealed 97% and 96% of average coverage over the reference melon genome database, respectively. A total of 57.51% non-synonymous SNPs and 42.49% synonymous SNPs were found, which produced 149 sets of codominant markers with a 24% polymorphism rate. Total 138-F₂ derived plant populations were genotyped for linkage mapping and composite interval mapping based QTL mapping exposed 6 genetic loci, positioned over distinct chromosomes (02, 04, 08, 09, and 12) between the flanking intervals of CAPS markers, which explained an unlinked polygenic architecture in genome. Three minor QTLs of fruit weight (FWt2.1, FWt4.1, FWt9.1), one major QTL of fruit firmness (FrFir8.1), one major QTL of fruit length (FL12.1), and one major QTL of fruit shape (FS12.1) were determined and collectively explained the phenotypic variance from 5.64 to 15.64%. Fruit phenotypic correlation exhibited the significant relationship and principal component analysis also identified the potential variability. Multiple sequence alignments also indicated the significant base-mutations in the detected genetic loci, respectively.

In short, our illustrated genetic loci are expected to provide the reference insights for fine QTL mapping and candidate gene(s) mining through molecular genetic breeding approaches aimed at developing the new varieties.