Propagation of Thuja × `Green Giant' by Stem Cuttings: Effects of Growth Stage, Type of Cutting, and IBA Treatment

Abstract

Stem cuttings of Thuja L. × `Green Giant', consisting of 22-cm terminals or 20-cm laterals, were collected on three dates associated with specific growth stages (softwood, semi-hardwood, and hardwood), and treated with indolebutyric acid (IBA) in 50% isopropanol ranging from 0 to 9000 ppm and placed under intermittent mist. Regardless of cutting type or auxin treatment, cuttings rooted in high percentages at each growth stage. Overall rooting was highest for hardwood cuttings (96%) followed by semi-hardwood (86%), and softwood (85%) cuttings. Semi-hardwood cuttings were the only cuttings in which rooting was affected by IBA or cutting type with the greatest rooting (94%) attained using lateral cuttings treated with 6000 or 9000 ppm IBA. Although an interaction occurred between IBA treatment and cutting type for mean root length of hardwood cuttings, only mean root length of semi-hardwood cuttings was influenced by IBA concentration alone with the greatest length (25 mm) achieved with 6000 ppm IBA. An interaction was noted for root count between cutting type and IBA concentrations for softwood cuttings, whereas IBA and cutting type affected independently root count on semi-hardwood cuttings. Treatment with 9000 ppm IBA resulted in 18 roots per rooted cutting whereas lateral cuttings responded with a mean of 16 roots over all IBA concentrations. Root count on hardwood cuttings was affected by IBA treatment only, with 9000 ppm being optimum (14 roots per rooted cutting).