Effects of High IBA Concentrations on Rooting and Root Development in Semi-Hardwood Black Mulberry (Morus nigra L.) Cuttings

Black mulberry (Morus nigra L.) is a small fruit species of high economic value, but its propagation by stem cuttings is often limited by low and inconsistent rooting performance. This study evaluated the effects of two high concentrations of indole-3-butyric acid (IBA) on rooting performance and root development of semi-hardwood black mulberry cuttings under greenhouse conditions. Cuttings collected from an 11-year-old mother plant were treated with 0 (control), 6000, or 7500 ppm IBA and rooted in perlite under mist propagation conditions. The experiment was conducted in a completely randomized design with four replications, each consisting of 12 cuttings per treatment. Survival rate, callus formation, rooting percentage, root number, root length, root branching, and root diameter were evaluated. Significant treatment effects were detected for all parameters except root diameter (p ≤ 0.05). The control showed the highest survival rate (80.08%), callus formation rate (31.24%), and rooting percentage (39.58%). In contrast, 7500 ppm IBA produced the highest root number (5.21 roots cutting⁻¹), root length (17.37 cm), and root branching rate (90.62%), although its rooting percentage (29.16%) was lower than that of the control. These findings indicate a trade-off between rooting success and root development under the tested conditions.