Effects of Plant Growth Regulator on Cutting Propagation of Rhododendron latoucheae

Using humus as a substrate, annual branch cuttings of Rhododendron latoucheae were treated with five plant growth regulators under four concentrations. In addition, the cuttings were also treated by naphthalene acetic acid (NAA) under different concentrations and soaking times. The effects of different treatment on cutting propagation were individually evaluated and the correlations of 12 propagation traits were studied. The propagation effects of each treatment combination were evaluated by the subordinate function method. The experiments showed that: gibberellic acid (GA₃) and indole-3-butyric acid (IBA) had positive effects on most propagation traits, followed by indole-3-acetic acid (IAA), 6-benzyladenine (6-BA) and NAA, suggesting that GA₃ and IBA could be ideal plant growth regulators for cutting propagation of R.latoucheae. Among the four concentrations of growth regulators, the lowest was generally the best treatment for callusing rate, rotting rate and retention rate of old leaves; however, as the concentration increased, it became less effective. The optimal concentrations for the other nine propagation traits varied among the five growth regulators. Correlation analysis of the propagation traits showed that the number of adventitious roots, length of longest adventitious roots, number of total roots and diameter of the root system had significant positive correlations, but little correlation with callusing rate, rotting rate, rooting rate, retention rate of old leaves and new shoot rate. Subordinate function evaluation showed that 50 mg/L GA₃ was the best treatment combination for cutting propagation of R.latoucheae, followed by 100 mg/L GA₃ and 400 mg/L IBA. This study can provide a scientific basis for the industrialization of rhododendron.