Clonal propagation of <i>Cinchona pubescens</i> Vahl (Rubiaceae) in nursery: influence of substrate composition and the commercial rooting regulator Root-Hor®

Red cinchona (Cinchona pubescens Vahl, Rubiaceae) is one of the most widely distributed species in the Peruvian Amazon; however, its populations are increasingly threatened by anthropogenic pressures, highlighting the need for effective propagation strategies. This study aimed to evaluate the effect of substrate composition and concentrations of the commercial rooting regulator Root-Hor® on the vegetative propagation of C. pubescens through mini-cuttings under nursery conditions. Three substrate mixtures were tested: S1 (soil:sand 1:1), S2 (2:1), and S3 (1:2, v/v), combined with four concentrations of Root-Hor® (0, 3, 5, and 7 mL L−1). Orthotropic shoots were collected from adult trees and established in a microtunnel system at 2,341 m a.s.l. Rooting, survival, callus formation, and root growth variables were evaluated after 60 days. The highest rooting percentage (95.7%) and superior root development (50 roots, 2.4 cm root length, and 60 mg fresh root weight) were achieved with the S2 substrate combined with 5 mL L−1 of Root-Hor®. In contrast, higher auxin concentrations promoted callus formation without improving rooting performance. These results demonstrate that the interaction between substrate physical properties and optimal auxin concentration is critical for successful adventitious root formation. The combination of soil:sand (2:1) and 5 mL L−1 Root-Hor® represents an efficient and low-cost strategy for the clonal propagation and conservation of C. pubescens in tropical ecosystems.