In Calluna vulgaris, a common bedding plant during autumn in the northern hemisphere, the bud-blooming mutation of flower morphology is of high economic importance. Breeding of new bud-blooming cultivars suffers from poor seed set in some of the desirable bud-flowering crossing partners. In the current study, fertilisation and seed development in genotypes with good or poor seed set were monitored in detail in order to examine pre- and post-zygotic cross breeding incompatibilities. Whereas no distinct differences were detected in seed development, pollen tube growth was impeded in the pistils of genotypes characterised by poor seed set. Detailed microscopic analysis revealed malformations of the gynoecia due to imperfect fusion of carpels. Hence, a pre-zygotic mechanism hindering pollen tube growth due to malformation of gynoecia was deduced. An interaction of putative candidate genes involved in malformation of gynoecia with floral organ identity genes controlling the flower architecture is discussed.

The ornamental crop Calluna vulgaris is of increasing importance to the horticultural industry due to a flower organ mutation, the so-called 'bud-flowering' phenotype, in which buds remain closed throughout the total flowering period and thereby maintain more colourful flowers for a longer period of time than the wildtype. Moreover, stamens are missing. In order to clarify the genetics of this mutation a comparative study of the wild-type and the 'bud-flowering' flower type of C. vulgaris was initiated. Scanning electron microscopic analyses of flower organs as well as gene expression studies of an AP3-like and a SEP1-like gene in the different flower whorls of both flower types allowed identification of bracts, sepals and petals. However, loss of stamens in the 'bud-flowering' phenotype could not be explained by modified spatial expression of known organ identity genes. Therefore, new approaches (map-based cloning and differential transcriptome analysis) are now envisioned in order to elucidate the genetics of the 'bud-flowering' phenotype.

The establishment of a marker-assisted selection system for the economically important 'bud-flowering' phenotype in the ornamental crop Calluna vulgaris is of great interest to practical breeding companies, as it would allow selection at the juvenile stage. Segregation analyzes revealed a monogenic recessive inheritance of the bud flowering trait. Since in C. vulgaris only sparse molecular data are available, the search for molecular markers in a segregating backcross progeny was accomplished using PCR techniques based on random primers. Two candidate RAPD markers in coupling of the trait of interest were identified. Results on their applicability in different populations and independent varieties are presented. Their transformation capability to sequence characterized amplified region and single strand conformation polymorphism markers are described and discussed in the context of marker-assisted selection strategies in breeding of ornamental crops.