Interspecific hybridisation and polyploidy are recognized as the most impor-tant sources of evolution and domestication of flowering plants. In ornamental plant breeding these phenomena go hand in hand and can be observed in the breeding his-tory of many ornamental crops (Rosa, Chrysanthemum, Gladiolus, Alstroemeria, Lil-ium, orchids etc). With lily as model crop techniques developed for overcoming pre- and post-fertilisation barriers are reviewed. For overcoming F1-sterility mitotic and meiotic polyploidisation are applied and can result in fertile allopolyploids. The mechanism of viable pollen production of mitotic and meiotic polyploidisation is quite different. Mitotic polyploidisation possess one homologous chromosome set. They undergo normal meiotic division like diploid cells. However, meiotic poly-ploidisation often show irregular chromosome division resulting in two of unreduced chromosome number instead of reduced chromosome number in tetrads. In contrast to mitotic doubling homoeologous recombination can occur. There are two signifi-cant mechanisms, FDR and SDR, for the formation of 2n-gametes. The FDR-gamete increase heterozygosity while SDR-gamete increase homozygosity. Genomic in situ hybridisation (GISH) has been used to discriminate parental chromosomes and to detect homoeologous recombination. Mitotic polyploidisation showed no homoeolo-gous recombinations between the parental genomes whereas in meiotic polyploids it can detected frequently. The use of 2n-gametes is therefore the most promising way for the introgression of desirable characters in the breeding with interspecific hy-brids. Although spontaneous occurring in the domestication of many ornamental crops the systematically detected unreduced gametes proved to be highly efficient tool for introgression of characters
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