Molecular Linkage Mapping in Bitter Gourd

Abstract

Genetic mapping of genes controlling agronomic traits and various phenotypes including the content of phytomedicines is essential for identifying their corresponding genes and linked markers for genetic improvement in bitter gourd. As studied in other crops, various molecular markers have been employed for genotyping including RAPD, AFLP, SSR, ISSR, etc. Recently, next-generation sequencing technology allowed to find a large number of DNA polymorphisms as molecular markers at a time. Sequencing-based molecular marker development, like RAD-seq or GBS, is equally applicable to even nonmodel plants as bitter gourd. Using molecular markers, several linkage maps were independently developed in bitter gourd. Although the number of analyzed markers and linkage groups was different among these maps, these maps were employed for QTL mappings. Currently identified QTLs in bitter gourd were mainly focused on the characteristics for flowers or fruits. These traits determine the quality or yield of the bitter gourd fruit. According to genetic mapping results, fruit color, fruit glossiness, fruit surface structure, stigma color, seed color, and gynoecy were suggested to be qualitative traits and determined by single or double loci. On the other hand, sex ratio, first node of female flower, days to first female flower, several traits for fruits (size, length, etc.) were found to be determined by several QTLs. Due to different mapping populations and employed molecular markers, correspondence among independently identified QTLs were still undetermined, but reference genome sequences of bitter gourd will be helpful for identifying corresponding genes for these QTLs in future.