The Role of Polyploidization and Interspecific Hybridization in the Breeding of Ornamental Crops

In the history of ornamental plant breeding, polyploidization can be observed as one of the most important processes in domestication, with a large effect on crop improvement. In the ornamental crops (Lilium, Tulipa, Narcissus and Begonia) exemplified here, the origin of the assortment of varieties traces back to the diploid species, from which the modern, predominantly triploid or tetraploid cultivars were created through spontaneous interspecific crosses or applied polyploidization techniques. The use of meiotic (2n gametes) and mitotic polyploidization as methods to obtain polyploids are discussed. The three restitution mechanisms of 2n gamete formation (Second Division Restitution (SDR), First Division Restitution (FDR) and Intermediate Meiotic Restitution (IMR)) and their genetic impact as elucidated by molecular cytogenetic techniques (such as Genomic In-Situ Hybridization (GISH)) are presented. Through GISH analysis the presence of intergenomic recombination, which is desirable for introgression breeding, was clearly demonstrated to occur in 2n gamete formation.