The Variable Effect of Polyploidization on the Phenotype in .

To induce new variation within the genus, chromosome doubling was performed in , and , three important species within this genus of mainly evergreen woody ornamental species. Obtained tetraploids and diploid controls were analyzed for rooting capacity, leaf and flower characteristics, and plant architecture using image analysis and cold tolerance. In the present study, a breeders' collection of 23 accessions was characterized cytogenetically and described morphologically. All analyzed species and cultivars were diploid (2n = 2x = 24), with exception of , a tetraploid. Today, breeding in is limited to lucky finds in seedling populations and few efforts in interspecific hybridization. Three selected species underwent an chromosome doubling with both oryzalin and trifluralin applied as either a continuous or shock treatment. The treatments successfully induced polyploids in all three species. Image analysis revealed that tetraploid had decreased shoot length (from 3.8 to 1.3 cm), higher circularity and more dense growth habit compared to diploids. No significant changes in cold tolerance were seen. Tetraploid did not differ in shoot length, but an increased outgrowth of axillary buds on the main axis led to denser plants. For tetraploid , an increase in plant height (from 4.9 to 5.5 cm) was observed together with a large decrease in circularity and density due to a more polar outgrowth of branches on the main axis. tetraploids bore larger flowers than diploids and had an increased cold tolerance (from -7.7 to -11.8°C). Leaf width and area of tetraploids increased for both and , while a decrease was seen in genotypes. For all three species, the rooting capacity of the tetraploids did not differ from the diploids. We conclude that the effect of polyploidization on was highly variable and species dependent.