Effects of Paclobutrazol Application and Soil Mulching on Flower Induction and Physiological Conditions in Durian Trees (Durio zibethinus Murr.)

In durian trees, flower induction is required to guarantee a consistent supply of durian fruit. Paclobutrazol (PBZ) is used extensively to stimulate flowering, and artificial drought stress may stabilize its effectiveness. We investigated the effects of PBZ application combined with drought stress on flower induction. We applied PBZ at three concentrations (0 [control], 1,000, and 1,500 ppm) on 9-year-old durian trees in an orchard in central Thailand 12 days after two groundcover treatments had been established (mulching versus bare ground). Then, we observed flower induction, soil water conditions, and the physiological conditions of the durian trees. Drought stress was confirmed in mulched trees: they had lower soil water potential, lower stomatal conductance, and very low leaf water potential (−0.9 MPa) compared to trees with bare ground. In both mulched and bare-ground trees, PBZ application did not induce flowering. Conversely, compared to the bare-ground treatment, mulching delayed flower bud emergence and the flowering date and reduced flower-cluster density. Therefore, we propose that strong drought stress, regardless of PBZ administration, inhibits flower induction in durian trees.