Effect of Girdling and Paclobutrazol on Growth, Plant Physiology, Inflorescence and Fruiting of Mangifera indica cv. Harumanis in Agroclimatic-Zone 3 of Peninsular Malaysia

Aims: This experiment aimed to study the effect of girdling, paclobutrazol application, combined methods, and untreated trees on physiological response, vegetative and reproductive growth, and fruiting. Place and Duration of Study: This study was carried out from August 2021 to June 2022 at MARDI, Serdang, Selangor, using five years of open-field Mangifera indica cv. Harumanis trees. Study Design:  The study was arranged in the frame of  randomized complete block design with three replications and three samples per treatment; ANOVA and DMRT at p=0.05 were used for significance and post hoc comparison, respectively. Methodology: Each replication consists of: T1- No induction (Control); T2- girdling at primary branches; T3- soil drenching at 4 ml/l PBZ and T4- girdling at primary branches + soil drenching at 4 ml/l PBZ. The girdling process was performed by removing a 10 mm width ring of bark at all primary branches. Paclobutrazol (25% active ingredient) of the commercial product was used. The treatments were performed concurrently on 1st December 2021 at the same morphological size as the tree subjected to similar light exposure. Results: The combination method of girdling and paclobutrazol application had the most significant adverse effect on internode length. Nevertheless, no significant difference was observed in plant stem diameter, height, number of primary and secondary branches, and number of shoots generated from all treatments. The combined method reflected a significant reduction in stomatal conductance, rate of photosynthesis, and transpiration rate. However, the intercellular CO2 concentration of this combined method and untreated tree is significantly higher. Flowering appears on the leaf buds 90 days after the treatment for paclobutrazol application and the combined method. These methods also resulted in yield per fruit and yield per tree. Conclusion: Based on the results, the combination method of girdling and paclobutrazol application was effective to reduce vegetative growth, suppress physiological capacity, yet the most effective to produce flowering and fruit yield.