The so-called "bud bloomers" are economically very important cultivars of Calluna vulgaris (Ericaceae), a major ornamental crop of the European horticultural sector. Within the bud bloomer group, the diplocalyx and the polystyla type can be distinguished. Both bud bloomer types have an extended flower longevity. Due to a dysfunction in flower opening, they display a duplication of calyx organs and a loss of petals. However, they differ with regard to flower whorl 3: whereas stamens are missing in the diplocalyx type, stamens show a carpelloid character in the polystyla type. The genetic basis of the bud blooming flower type is still unclear. A series of crosses was performed to evaluate the number of loci and alleles involved in the genetics of the trait 'flower type' in C. vulgaris. From the segregation ratios within the resulting populations, a monogenic inheritance involving three alleles was deduced, assuming that the polystyla genotypes are heterozygous. This hypothesis was verified in additional crossing experiments.

Heather (Calluna vulgaris), an important bedding plant in Northern Europe, is a monotypic genus with rather limited phenotypic variability. Hence, it is aimed at starting a breeding program of polyploids that might constitute a new phenotypic class of varieties with attractive strong habitus and larger flowers. As a basis, data on fertility of genotypes of different ploidy levels, fertility of interploid crosses, and ploidy levels of the offspring were generated by setting up a complete interploid crossing experiment in C. vulgaris including diploid (2x), triploid (3x), and tetraploid (4x) genotypes.Determination of pollen viability by staining, in vitro germination and evaluation of pollen tube growth in vivo generated contradicting results and none of the methods proved to be suitable to explain fertilization success as determined by seed set. Seed yield was significantly reduced in any cross direction compared to 2x x 2x crosses. However, the germination rate did not correlate with seed set, hence for determining crossing success, the number of germinating seedlings has to be considered. The rate of germinating seedlings per pollinated flower was 2.95 in the 2x x 2x crosses and on average only 0.025 in the interploid crosses. 2x x 4x and 4x x 2x crosses differed significantly with regard to seed yield, germination rate and ploidy of the offspring. 3x genotypes were generated only by 4x x 2x crosses. Aneuploids resulted from 2x x 3x, 3x x 4x, 4x x 2x and 4x x 3x crosses. (C) 2014 Elsevier B.V. All rights reserved.

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.