Mini-cutting size, mini-tunnel management and phytohormones in the clonal propagation of Eucalyptus urophylla and hybrids of Corymbia spp.

The area planted with Corymbia spp. clones is expected to increase in the coming years, despite their propagation challenges. This study aimed to evaluate mini-cutting size, mini-tunnel opening time, and the use of growth regulators in the clonal propagation of Corymbia spp. Four experiments were conducted using three clones: C. citriodora × C. torelliana, C. torelliana × C. citriodora, and E. urophylla, where E. urophylla was used as a control due to its ease of propagation. The results from each experiment were used to optimize the methodology for the subsequent one. Initially, three mini-cutting sizes were tested: 5, 10, and 15 cm in length. The second experiment evaluated three collection times of mini-cuttings after mini-tunnel opening: 0, 24, and 48 hours. The third experiment tested five concentrations of indole-3-butyric acid (IBA): 0, 500, 1000, 1500, and 2000 mg kg⁻¹. Finally, five concentrations of a formulated product containing different plant growth regulators (0, 1, 2, 3, and 4 mL L⁻¹) were assessed. All experiments were arranged in a randomized block design in a factorial scheme according to genotype. The following variables were evaluated: final rooted mini-cutting yield, survival, plant height, root length, and root, shoot, and total dry mass. Mini-cuttings of 15 cm performed best in promoting the growth of both hybrids. Regarding mini-tunnel opening time, the 24-hour interval after opening was optimal for C. citriodora × C. torelliana. Applications of 2000 and 1000 mg kg⁻¹ IBA promoted rooting in Corymbia spp., and rooted mini-cutting quality was improved with the application of 4 mL L⁻¹ of the growth regulator formulation.