Influence of deficit irrigation and paclobutrazol on plant growth and water status in Lonicera implexa seedlings

Mediterranean honeysuckle (Lonicera implexa) is the subject of great interest for xeroscaping and revegetation projects. Seedling pre-conditioning in the nursery is critical to achieve success in the establishment phase. The objective of this experiment was to evaluate the effect of irrigation regime [control (20% leaching) and deficit (43% of the control)] and paclobutrazol (PBZ) doses [control (0 mg/pot) and treated (80 mg/pot)] on growth parameters, water relations and gas exchange in honeysuckle plants during the nursery period. Seedlings were potted in 2.5 L pots and grown in a greenhouse located in the Campo of Cartagena (Spain). At the end of the experimental period, both deficit irrigation and PBZ significantly reduced shoot development. Significant interaction between the irrigation regime and PBZ doses was evident for plant height and stem diameter. The shoot/root ratio was not affected by the deficit irrigation and PBZ dose. Both the deficit irrigation and PBZ dose increased significantly the relative chlorophyll content in the leaves. Plants grown under deficit irrigation had lower values of water leaf potential, leaf osmotic potential and relative water content than the control plants. PBZ-treated plants had increased leaf water potential and turgor potential and had reduced leaf osmotic potential at full turgor. Significant interaction between the irrigation regime and PBZ dose was evident for the leaf water potential and leaf osmotic potential, demonstrating that PBZ attenuates the effects of deficit irrigation. The stomatal conductance decreased at the end of the hardening stage by 63% in plants grown under deficit irrigation and was not affected by PBZ dose. The results suggest that deficit irrigation and PBZ modify the plant growth and water status of honeysuckle plants improving the resistance mechanisms related to the plant adaptation to drought conditions.