Influence of clonex and indole-3-butyric acid on the rhizogenesis of Picea pungens f. glauca cuttings

The study aimed to provide a quantitative assessment of the effects of different concentrations of indole-3-butyric acid (IBA) and gel-based formulations on the intensity of rhizogenesis in semi-hardwood cuttings of Picea pungens f. glauca, with the objective of identifying the most effective treatment options. Over a three-year period (2023-2025), the efficacy of Clonex Green, Clonex Purple, and Clonex Red, as well as aqueous IBA solutions at concentrations of 1,000, 3,000, and 5,000 mg L-1, was evaluated in the propagation of semi-hardwood cuttings of Picea pungens f. glauca. Cuttings 8-12 cm in length were collected from stock plants up to 10 years of age and established in a substrate composed of a 1:1 mixture of river sand and highmoor peat. The results demonstrated that the application of Clonex formulations and IBA significantly increased the rooting percentage compared with the control treatment, where the mean value was only 5.6%. The highest efficacy was achieved with the gel formulation Clonex Purple, which resulted in a rooting percentage of 37.8%. High effectiveness (28.9%) was also observed with Clonex Green and with the aqueous IBA solution at a concentration of 1,000 mg L-1. It was found that a further increase in the concentration of pure IBA to 3,000 mg L-1 led to a decrease in rooting to 24.4%, while the application of 5,000 mg L-1 caused a pronounced inhibition of rhizogenesis (11.1%), indicating a phytotoxic effect. Gel-based stimulants (Clonex) were shown to outperform aqueous solutions, which can be attributed to prolonged contact of the active substance with the base of the cutting, its gradual release, and protection against leaching from the substrate. Statistical analysis using analysis of variance confirmed the significance of the observed differences (LSD0.05 = 1.71-1.83). The findings provide a basis for recommending optimal concentrations of growth stimulants to improve the production of high-quality planting material of ornamental coniferous species