Construction of a high-density genetic map and mapping of double flower genes in petunia

•17 SCAR markers linked to double flower trait of petunia hybrida was developed.•A high-density genetic map was constructed with 4474 SNP markers.•The double flower genes in petunia were first mapped to a genomic region of 1.82 Mb. Double flower (DF) is one of the important ornamental traits of horticultural plants, but the molecular mechanism of its formation is still unclear. In this study, forward genetic approaches were applied to explore the key genes involved in the DF formation in petunia. We developed a total of 17 SCAR markers linked to DF, and initially mapped the DF genes onto 9 scaffolds (totally 13.3 Mb) in the genome of the DF petunia. We also constructed a genetic linkage map of petunia, which contained 4474 SNP markers, with a total genetic distance of 2022.786 cM and an average genetic distance of 0.758 cM. In QTL analysis, a QTL associated with DF trait was detected. The LOD value of the marker was 3.82–12.71, and the contribution rate was 16.0 %–44.0 %. To further shorten the mapping interval of the DF genes, we constructed a near-isogenic line (NIL) population containing 2757 plants, and used these 17 SCAR markers to screen the recombinant plants, and located the DF genes within a 2.2 Mb interval. Combined with Bacterial Artificial Chromosome (BAC) library screening, the mapping interval of the DF genes was ultimately shortened from 2.2 Mb to 1.82 Mb. Presently, research on the DF trait of petunia mainly focused on the ABC(D)E model. The fine mapping results of petunia DF genes obtained in this study provide a new idea for revealing the molecular mechanism of DF formation in petunia.