Jadrná P., Plavcová O., Kobza F., 2010. Morphological changes in colchicine-treated Pelargonium × hortorum L.H. Bailey greenhouse plants. Hort. Sci. (Prague), 37: 27-33.Polyploids were effectively pre-selected in colchicine-treated plants of the desirable brown-leaved cultivar Black Velvet Scarlet F1 of the species Pelargonium × hortorum L.H. Bailey to obtain the basic breeding material for creating new brown-leaved tetraploid cultivars. The green-leaved cultivar Gizela F1 was used for comparison of quantity and quality of response to colchicine treatments. Water solutions of colchicine in the range from 0.1% to 2.5% induced polyploidy in seedlings with treatments repeated each day for 2, 3, 5 or 7 days. Polyploid plants were pre-selected according to their morphological changes and stomata length and density and verified using flow cytometry. Some morphological changes (leaf coloration, flower shapes) in colchiploids differed between the genotypes, others were the same in both cultivars (loss of coloration in mixoploids, failure of blooming).

31Cultivars of Pelargonium × hortorum with attractive black leaves with a narrow green margin are relatively new. The first cultivar of this type was Black Velvet Rose F1, bred in Silva Tarouca Research Institute for Landscape and Ornamental Gardening (VÚKOZ) Průhonice in 1996 (the original name was Black Magic Rose F1; later the name of the whole series was changed to Black Velvet). The first cultivars of this diploid black-leaved F1 series were awarded for their originality and quality (Plavcová 2007).We aimed our work at induction of polyploidy in a cultivar from the Black Velvet series to obtain basic breeding material for creation of new black-leaved tetraploid cultivars with double or full flowers.Tetraploid cultivars of zonal pelargonium have larger flowers that are mostly double or full. The colours of flowers are often more interesting because of higher amount of genetic information in tetraploid cells.Nevertheless, the most important advantage of tetraploid cultivars (from a customer's point of view) is lower flower fertility, typical for autotetraploid plants due to disorders in segregation and dislocation of chromosomes in meiosis (Acquaah 2007). This means that the flowers remain blooming for much longer time, whereas after fertilization they would lose their petals and begin creating seeds, which is an unfavourable attribute for ornamental flowering plants. Thus, tetraploid cultivars of zonal pelargonium can be more interesting than diploid cultivars. This character however represents problems for plant breeders that they obtain fewer seeds for their work compared to diploid plants. Even so, it is profitable to have breeding programs for tetraploid pelargoniums because of their market importance (Hofmann 1992). MATERIALS AND METHODSTwo diploid F1 cultivars of Pelargonium × hortorum L. H. Bailey, a black-leaved cultivar with orangered flowers Black Velvet Scarlet F1 and a comparative green-leaved cultivar Gizela F1 with a standard type of leaf zone and bright-red flowers, were chosen to induce polyploidy in their seedlings. Seeds of these cultivars were sown into trays (each tray with Czech RepublicABSTRACT: This study is aimed at induction of polyploidy in the black-leaved cultivar Pelargonium × hortorum L. H. Bailey Black Velvet Scarlet F1 to obtain basic breeding material for creating new black-leaved tetraploid cultivars. The cultivar Gizela F1 was chosen as a control for the experiment. Tetraploidy was induced in seedlings in the cotyledon stage using various concentrations (from 0.1 to 2.5%) of colchicine water solutions; the treatments were repeated daily for 2, 3, 5 or 7 successive days. The first experiment, done in 2005, was very successful; 17.4% of treated Black Velvet Scarlet F1 plants and 23.7% of treated Gizela F1 plants were tetraploid, and other ploidy levels were also found. However, two other replications from 2006 (involving only five best treatments from the first experiment) were much less successful in comparison with the first one.