Fifty shades of red: flavonoid analysis in Rhododendron simsii hybrids

Flower colour is still one of the most important features of pot azalea breeding (Rhododendron simsii hybrids). We already built a genetic linkage map of a population segregating for flower colour. The map includes a small set of functional markers for flower colour biosynthesis. The flower colour was in the first phase objectively phenotyped by means of RGB values. More recently also the CIEL*a*b* colour space was used on 3 replicates for every sibling to get an even more reliable parameter for QTL mapping of the petal colour phenotype. Gene expression data of key genes of the flavonoid biosynthesis pathway were generated by means of RT-qPCR and were mapped as eQTLs (expression QTLs). To enlarge the amount of functional markers for flower colour, Illumina HiSeq PE-100 sequencing was performed on RNA of 3 pools of samples: red, pink and white flowers (10 genotypes per pool). A broad set of candidate genes will be filtered from this dataset for SNP development. Differential gene expression between flower colour groups will be validated by means of RT-qPCR in order to determine what is behind differences in flower colour intensities. To enrich further the map value with mQTLs (metabolite QTL), we started to analyze pigment composition using LC-MS/MS. The quantity of five anthocyanidins and four flavonols known to be commonly present in azalea flowers was measured. The different results for the three flower colour groups will be discussed.