K-Iba Concentration Regulated Rooting Quality and Plant Vigor of Prunus laurocerasus L.

Prunus laurocerasus L. is an evergreen species of Rosaceae, native to southwestern Asia and southeastern Europe. It is a widely cultivated ornamental plant in gardens and parks in temperate regions. A new type of branch sprout with 2–4 cm long and 0.5–1.5 cm broad leaves was collected and regenerated with the stem cuttings in November 2012. All cuttings were treated with K-IBA at 1000, 3000, and 8000 mg·L^-1. K-IBA concentrations had significant influence on rooting quality and after growth of Prunus laurocerasus. The rooting percentage was very high, ranging from 94.4% to 100% after two months. Although the rooting percentage did not show a great difference, the number of roots and root length were highly affected. As the K-IBA concentrations increased, the number of roots increased significantly from 6 to 11 to 17.  However, root length had the opposite trend than that of root numbers. The longest root length, 21.9 cm, was obtained from cuttings treated with K-IBA at 1000 mg·L^-1. Cuttings treated with K-IBA 1000 mg·L^-1 had a mean root length of 6.2 cm, 4.8 and 1.9 cm for 3000 mg·L^-1 and 8000 mg·L^-1, respectively. Rooted cuttings were transplanted to one-gallon pots and placed in a heated greenhouse. The survival rate was recorded and dead cuttings were examined. The highest survival rate was 95.5% under K-IBA 1000 mg·L^-1 treatment, while those treated with K-IBA 3000 mg·L^-1 and 8000 mg·L^-1 was 78.8% and 50.0%, respectively. Higher K-IBA concentrations might increase the number of roots, but kill the rooted cuttings or reduce the plant vigor afterward. For the propagation of Prunus laurocerasus, stem cuttings treated with K-IBA 1000 mg·L^-1 are recommended.