Improving the rooting capacity in cutting of box tree, an endangered ornamental shrub

Box tree (Buxus sempervirens L. or Buxus hyrcana Pojark.), Buxaceae, is an ornamental shrub that has application in various industries. This shrub is using extensively for landscape design and gardens. Growth and development of box tree is very slow, and under danger of extinction due to the invasion of some pathogens. Root induction in cuttings causes the faster propagation of the plant. Thus, the aim of this research was to improve the rooting condition of hard-rooting scions of box tree and achievement of the best concentration of hormones treatments of IBA and NAA among 0, 500, 1000, 2000 and 3000 mg l-1. In order to investigate the effect of different consentrations of IBA and NAA, an experiment was carried out as factorial based on a randomized complete block design in four replications. Treatments were 0 (as control), 500, 1000, 2000 and 3000 mg l-1) of both treatments of IBA and NAA, singular and in combination. In autumn, the 15-20 cm of shoot tips of the 2-years-old mother plants were dissected and used as hardwood cutting. Lower end of the shoot tip cuttings was kept in different concentrations of IBA and NAA and then was planted in cultivation bed. In this research, rooting percentage, root number, root length, plant height, leaf surface, leaf number, the longest root number and root fresh and dry weights were calculated. Cultivation bed of cuttings was perlite. The end of cuttings was put in 400 mg l-1 silver Nano-particle solutions for 10 sec. to prevent of probably infection. The results of analysis of variance showed that the reciprocal effect of different concentrations of plant growth regulators (IBA and NAA) was significant on all traits at 5% and 1% of probability levels, except for plant height. Results showed that the highest rooting percentage (100%) and maximum root number (8.70/plantlet) were observed in cuttings treated with 1000 mg l-1 NAA along with 1000 mg l-1 IBA. Also, the highest root length (5.66 cm/plantlet) was recorded in cuttings treated with 2000 mg l-1 NAA plus 1000 mg l-1 IBA. Treatment of 1000 mg l-1 NAA along with 1000 mg l-1 IBA induced the more extension of leaf surface than the other treatments. The largest number of leaf (33.37 per plant) was calculated in cuttings treated with 3000 mg l-1 NAA along with 500 mg l-1 IBA. Cuttings treated with different concentrations of IBA and NAA had different fresh weight and dry weight. B. hyrcana may be successfully propagated by stem cuttings. Plant growth regulators especially auxins have effective role on increasing the rooting of hard-rooting cuttings in trees and shrubs. Two hormons of IBA and NAA can be effective on improvement of rooting of B. hycana stem cuttings. A concentration of 1000 mg l-1 NAA along with 1000 mg l-1 IBA induced the better rooting than other hormonal treatments