Modulating Morphological Architecture: The Role of Paclobutrazol in Inducing Compactness and Pseudobulb Expansion in Dendrobium Orchids

Aims: To evaluate best concentration of Paclobutrazol (PBZ), a gibberellin biosynthesis inhibitor, on the growth and flowering characteristics of Dendrobium ‘TC 32’ to achieve a compact, sturdy growth habit suitable for commercial pot plant production. Study Design: The experiment utilized a Randomized Complete Block Design (RCBD). It was conducted under glasshouse conditions with 70% shade at the Floriculture Research and Development Unit (FRDU), Department of National Botanic Gardens, Peradeniya, Sri Lanka. Methodology: Two-year-old, sixty tissue-cultured plants (average height 23.25 cm) were treated with four concentrations of PBZ: 0.0 (control), 0.2, 0.4, and 0.6 mg/L (T1–T4). Growth parameters (tiller height, pseudobulb circumference, leaf production and tiller production) were monitored from November 2023 to October 2025. Floral quality (flower count and spike height) was recorded bi-weekly following spike initiation in May 2024. Results: Higher concentrations of PBZ significantly influenced plant architecture (P < 0.001). Height: T4 (0.6 mg/L) resulted in the shortest plants, with a mean tiller height of 9.37± 1.50 cm (F=163.78, P<0.001) and a mean spike height of 8.9 ± 1.03 cm (F=648.74, P<0.001. PBZ treatment significantly increased pseudobulb circumference 8.93 ± 0.96 cm (F= 32.89, p< 0.001). There was no significant effect on the total number of flowers 9.33±1.23, (F=1.04, P=0.381), tiller count 3.93 ± 0.80 (F=2.40, P= 0.077) or leaves produced 6.60±1.06, (F=0.46, P=0.71). (P>0.05) Conclusion: Paclobutrazol effectively induces dwarfism and increases pseudobulb robustness in Dendrobium orchids. To balance growth retardation with overall plant vigor, T2 (0.2 mg/L) is recommended as the most suitable concentration for producing high-quality, compact flowering Dendrobium ‘TC 32’ under local glasshouse conditions in Sri Lanka.