Post-transplanting performance of hardened honeysuckle (Lonicera implexa) seedlings after drought and PBZ hardening in nursery

Honeysuckle (Lonicera implexa Aiton) is of great interest in xerogardening and landscaping projects, although the pre-conditioning treatments used in the nursery are crucial for the establishment and subsequent growth in semi-arid conditions. Seedlings were grown in 2.5 L pots in unheated greenhouse near the Mediterranean coast of SE Spain, from November 2005 to May 2006. After a 30- days acclimation period the plants were subjected to a single drench of 80 mg of paclobutrazol (PBZ). Untreated plants acted as control. Additionally, all the plants were subjected to two irrigation regimes: well irrigated (control), irrigated to 100% of the water-holding capacity (WHC) and deficit irrigation, irrigated to 50% of the WHC. At the end of the nursery period, both deficit irrigation and PBZ significantly reduced shoot development. Significant interaction between the irrigation and PBZ was observed for plant height and stem diameter, while the shoot/root ratio was unaffected by both deficit irrigation and paclobutrazol. Seedlings from all treatments were transplanted into 6 L containers. They were watered once a week to 100% of the WHC for three weeks, after which, and until the end of the experiment (19 July, 2006), they received no water (establishment period). Differences in survival rate were observed among treatments. The combined effect of both paclobutrazol and deficit irrigation reduced significantly the mortality rate after transplanting under harsh conditions. The shortest survival rate occurred in both PBZ-untreated and well irrigated plants during the nursery period. Plant survival rate was affected by paclobutrazol, while the same was not observed with deficit irrigation. These results suggest that, although deficit irrigation induced physiological changes in plants, these were insufficient to improve survival rate under harsh conditions, whereas the application of PBZ in both control and deficitirrigated plants improved significantly the drought tolerance.