Potential Impact of Gibberellin Inhibitors on Flowering Bud Differentiation and Metabolite Dynamics in Mango (Mangifera indica L.) cv. Irwin

Abstract

Rising global air temperatures have led to the increased greenhouse cultivation of mango (Mangifera indica L.), particularly in southern South Korea. However, excessive vegetative growth in mango trees hinders reproductive growth and fruit production, posing a challenge for greenhouse farming. High gibberellins (GAs) levels during flower bud differentiation can hamper the process, reducing flowering and fruiting. This pilot study investigated the effects of paclobutrazol (PBZ) and prohexadione-calcium (Pro-Ca), known inhibitors of GA, on flower bud differentiation and panicle development in mango trees grown under greenhouse conditions. Two treatment groups were established: PBZ once and twice (1,500 ppm in 22.9% suspension concentrate), and Pro-Ca once and twice (500 ppm in 20% suspension concentrate). Treatments were applied in July of 2022 after shoot hardening following summer pruning, coinciding with the flower bud differentiation induction period (mid-November 2022 to mid-January 2023). During this period, the average temperature and average relative humidity were 13.4°C and 62%, respectively. Reproductive growth changes were observed through seven stages. The PBZ once and twice treatments reached stage 2 (floral bud initiation) most rapidly, followed by Pro-Ca once and twice, and the control group, all within four days. Notably, there were no significant differences in fruiting between the treatments and control. Regarding panicle characteristics, PBZ twice produced the longest panicles, while Pro-Ca twice yielded the shortest. However, the panicle width remained similar across all groups. The findings suggest that the PBZ twice, Pro-Ca once and Pro-Ca twice treatments effectively promote flower bud differentiation and improve panicle quality based on growth characteristics. Furthermore, a subsequent GC-MS analysis and heatmap profiling found that eight key metabolites were present in all samples, including the control and treatment groups, all of which being involved in the mango flowering responses. Overall, GA inhibitors showed promising effects on the transition to flower bud differentiation induction.