Development and validation of a novel marker for fruit bitterness in cucumber (Cucumis sativus L.)
摘要
The cucumber fruit bitterness is caused by cucurbitacins, which are a specific group of bitter tetracyclic triterpenoids, and they markedly diminish the eating quality and market value. Breeding for non-bitter cucumber cultivars is complicated, because the expression of bitterness is influenced by various environmental factors. This challenge is evident in Korean cucumber varieties with conditional bitterness, but no robust molecular markers are available for environment-independent marker-assisted selection (MAS). Whole genome re-sequencing (WGRS) was performed on eight cucumber lines. The sequencing achieved over 98% coverage of the cucumber reference genome and it uncovered a novel and conserved single nucleotide polymorphism (SNP) in the intergenic region downstream of CsBt on chromosome five. The SNP was developed into a diagnostic derived cleaved amplified polymorphic sequences (dCAPS) marker, CsBt_dCAPS. The phenotypic evaluation in the F₂ segregating population revealed a 9:7 (bitter: non-bitter) segregation ratio, which is consistent with a complementary epistatic interaction. The CsBt_dCAPS marker segregated in a co-dominant manner and it showed a genotype–phenotype concordance of 81.7%, which does not attribute fruit bitterness to a single-gene model. These results support a CsBi-centered model of cucumber fruit bitterness, and the CsBt and other CsBt-independent loci likely activated CsBi and contributed to the phenotype. The CsBt_dCAPS marker improves the efficiency of MAS for fruit bitterness.