Modulating Morphological Architecture: The Role of Paclobutrazol in Inducing Compactness and Pseudobulb Expansion in Dendrobium Orchids
W. M. D. N. Warigajeshta *
Landscape Division, The Open University of Sri Lanka, Nawala, Nugegoda, Sri Lanka.
M. D. E. R. Andradi
Floriculture Research and Development Unit, Department of National Botanical Gardens, Peradeniya, Sri Lanka.
S. A. Krishnarajah
Floriculture Research and Development Unit, Department of National Botanical Gardens, Peradeniya, Sri Lanka.
*Author to whom correspondence should be addressed.
Abstract
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.
Keywords: Dendrobium, floriculture, plant growth regulators, paclobutrazol, dwarf, salk length, potted plants