Development of Bi gene-based SNP markers for genotyping for bitter-free cucumber lines

High contents of cucurbitacin compounds result in a bitter taste in cucumbers. The Bi locus mapped to chromosome 6 is responsible for cucumber bitterness. The Bi gene encodes oxidosqualene cyclase, a key enzyme in the cucurbitacin biosynthetic pathway. Two alleles of the Bi gene responsible for the phenotypic variation in bitterness differ by a single point mutation in the coding region. An efficient genotyping system is necessary to allow breeders to screen for bitterness alleles in their breeding programs. In the present study, the single nucleotide polymorphism located within the Bi gene, which is directly linked to cucumber bitterness, was utilized for gene-based marker development. We developed reliable and cost-effective high-resolution melting (HRM)- and Kompetitive Allele-Specific PCR (KASP)-based molecular markers (BiHRM1 and Bi-KASP). These gene-based markers should enhance the accuracy and effectiveness of marker-assisted selection for bitter-free cucumber lines in cucumber breeding programs.