IBA, Juvenility, and Position on Ortets Influence Propagation of Carolina Buckthorn from Softwood Cuttings

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Abstract Carolina buckthorn (Rhamnus caroliniana Walt.) has horticultural potential but is not often propagated or grown as a nursery crop. My objective was to determine how three concentrations of indolebutyric acid (IBA) affect foliar quality of cuttings, callus development, and rooting of terminal and subtending softwood cuttings from both juvenile and mature stock plants (ortets). Twelve cuttings were assigned to each of 12 factorial treatment combinations and held under intermittent mist for five weeks. Fewer than 10% of cuttings not treated with IBA rooted. Rooting ≥75% resulted when IBA at 3 or 8 g/kg (3000 or 8000 ppm) was applied unless the cuttings were from terminal positions on mature ortets. High quality and dry weight of leaves were associated with subtending cuttings that were juvenile and with terminal cuttings that were mature, but these foliar traits did not lead to particularly high rooting percentages. Juvenile cuttings with IBA at 8 g/kg (8000 ppm) formed the most primary roots and developed root systems with the greatest weight, and dry weight of roots on juvenile cuttings that were subtending (25.6 mg) was about four times that ofjuvenile, terminal cuttings (6.5 mg). The longest individual roots were on juvenile cuttings with IBA at 3 or 8 g/kg (3000 or 8000 ppm). Frequency of callus on the cut end of stems decreased as IBA concentration increased and was 94 and 75%, respectively, for cuttings from juvenile and mature ortets. Nearly all cuttings with IBA at 3 or 8 g/kg (3000 or 8000 ppm) developed callus on wounds that had been made along the sides of their stems. The frequency of side callus was greater for juvenile, subtending cuttings than for juvenile, terminal cuttings; the opposite was true for mature cuttings. These results confirm the sensitivity of stem cuttings of Carolina buckthorn to IBA. The data also demonstrate that use of subtending wood will improve rooting percentages of cuttings from mature ortets, and that use of subtending cuttings from juvenile plants and of IBA at 8 g/kg (8000 ppm) will increase the number and dry weight of roots.