Genome-wide association study overcomes the genome complexity in autohexaploid chrysanthemum and tags SNP markers onto the flower color genes

The use of DNA markers has revolutionized selection in crop breeding by linkage mapping and QTL analysis, but major problems still remain for polyploid species where marker-assisted selection lags behind the situation in diploids because of its high genome complexity. To overcome the complex genetic mode in the polyploids, we investigated the development of a strategy of genome-wide association study (GWAS) using single-dose SNPs, which simplify the segregation patterns associated polyploids, with respect to the development of DNA markers. In addition, we employed biparental populations for the GWAS, wherein the SNP allele frequency could be predicted. The research investigated whether the method could be used to effectively develop DNA markers for petal color in autohexaploid chrysanthemum (Chrysanthemum morifolium; 2n = 6x = 54). The causal gene for this trait is already-known CmCCD4a encoding a dioxygenase which cleaves carotenoids in petals. We selected 9,219 single-dose SNPs, out of total 52,489 SNPs identified by dd-RAD-Seq, showing simplex (1 x 0) and double-simplex (1 x 1) inheritance pattern according to alternative allele frequency with respect to the SNP loci in the F-1 population. GWAS, using these single-dose SNPs, discovered highly reproducible SNP markers tightly linked to the causal genes. This is the first report of a straightforward GWAS-based marker developing system for use in autohexaploid species.