Synthetic Small Molecules as Regulators of In Vitro Multiplication in Selenicereus Hybrids

Micropropagation of Selenicereus hybrids is a key tool for breeding and conservation; however, further refining the balance between high multiplication rates and morphological quality remains a complex challenge within conventional protocols. This study explores targeted signaling modulation using nine bioactive small molecules—including three mammalian glycogen synthase kinase 3 (GSK3) inhibitors (TDZD-9, VP3.15 and VP0.7), three leucine rich repeat kinase 2 (LRRK2) inhibitors (JZ1.24, JZ1.3 and IGS4.75), and three phosphodiesterase (PDE) inhibitors—to complement traditional micropropagation. Explants were evaluated in two distinct contexts: a hormone-free basal medium (BM) and a plant growth regulator-supplemented medium (PIT2) and the response rates, yield, and quality were measured and integrated using a Global Efficiency Index (GEI). Results demonstrate that inhibitor efficacy is strictly context-dependent; while most molecules repressed budding in BM, they acted as response modulators by determining the specific type of morphogenic pathway in PIT2. Notably, the GSK3 inhibitor TDZD-9 reached the highest GEI (0.85) by maximizing productivity, whereas LRRK2 inhibitors effectively preserved architectural integrity. Flow cytometry confirmed cytogenetic stability across all treatments, with a 98.5% plantlet survival rate during acclimatization. In conclusion, the strategic integration of targeted signaling modulators and multi-parametric indices offers a refined and objective framework to enhance the efficiency of mass propagation protocols in pitahaya and other recalcitrant species. Furthermore, our findings provide new evidence of the strong potential of these small molecules as novel tools to improve plant micropropagation beyond traditional plant growth regulators.