In Vitro Chromosome Doubling of Prunus laurocerasus 'Otto Luyken' and 'Schipkaensis'

Prunus laurocersaus L. (2n = 22x = 176), common cherrylaurel, is an evergreen shrub generally used as a hedge or screen. This species produces large drupes that are a nuisance when they drop on walkways or deposited by birds and also has escaped cultivation in parts of northwestern United States, which has raised concern about the invasive potential of common cherrylaurel. Therefore, a fruitless and sterile form of common cherrylaurel is desirable. As part of our efforts to develop sterile common cherrylaurel cultivars, we conducted two experiments to induce chromosome doubling using in vitro exposure of 'Otto Luyken' and 'Schipkaensis' cherrylaurel to oryzalin. For 'Otto Luyken' (Expt. 1), we tested the effects of treatment duration (1, 2, 14, or 28 days) and oryzalin concentration (0, 6.25, 12.5, 25, 50, 100, or 150 mu M) applied in a liquid phase over explants. In Expt. 2, we treated 'Schipkaensis' cherrylaurel shoots with a single duration of 28 days and exposed explants to the same varying concentrations of oryzalin incorporated into the solidified medium. In Expt. 1, the 14-day treatment had reduced survival compared with 1-and 2-day treatments and there was still greater mortality in the 28-day treatment. Duration of the treatment affected mortality more than oryzalin concentration. Sixteen treatment combinations resulted in 44x plants. The percentage of 44x plants increased with concentration in the 1-and 2-day treatments up to 30% of treated shoots at 150 mu M. Overall, the longer duration treatments in Expt. 1 were less efficient for inducing 44x plants. Expt. 2 was less effective for inducing homogenous 44x plants. It is unclear if this is due to treatment or cultivar differences but the highest concentration was 8% in the 6.25 mu M treatment.