Strigolactone pathway genes and plant architecture: association analysis and QTL detection for horticultural traits in chrysanthemum.

Chrysanthemums are important ornamental plants with abundant phenotypic diversity. Especially in cut-flower breeding, shoot branching is important for the success of new varieties. To assess the genetic regulation of shoot branching and other horticultural important traits, we phenotyped and genotyped two types of chrysanthemum populations: a genotype collection of 86 varieties and a biparental F1-population (MK11/3) of 160 individuals. Using two different statistical approaches, a genome-wide association analysis and a single marker ANOVA, with AFLP marker data and candidate gene markers for shoot branching, we tried to identify markers correlated to the traits of interest. As expected for the outcrossing hexasomic chrysanthemums most of the phenotypic traits showed a continuous variation in both populations. With the candidate gene approach we identified 11 significantly associated marker alleles for all 4 strigolactone pathway genes BRC1, CCD7, CCD8 and MAX2 regulating shoot branching in the genotype collection. In the MK11/3 we detected seven markers for all candidate genes except MAX2 explaining a large proportion of the variation. Using anonymous AFLP markers in the GWA with the 86 genotypes and the single locus analysis with the F1-population we could detect 15 and 17 additional marker-trait associations, respectively. Our analyses indicate a polygenic inheritance of the shoot branching in the chrysanthemum, with a fundamental role of the strigolactone pathway genes BRC1, CCD7, CCD8 and MAX2 and we identified 50 associated markers to all traits under study. These markers could be used in the selection of the parental plants for breeding chrysanthemums to enrich them for positive alleles influencing plant architecture traits.