The aim of this study was to analyse the effect of regulated deficit irrigation (RDI) on growth and development of potted rhododendron ‘Catawbiense Boursault’ and ‘Old Port’ plants and to evaluate the usefulness of this technique for saving water in nursery production and promoting flowering. Plants were grown in 1.9 litre plastic containers in unheated greenhouse and were subjected to six irrigation treatments lasting for 14 weeks from June to mid-September. A drip irrigation system with one 2 dm3·h-1 emitter per container was used. Six treatments of irrigation were applied: T1) 1 ETp (evapotranspiration) (control, well watered plants); T2) 0.75 ETp (moderate deficit irrigation); T3) 0.5 ETp (strong deficit irrigation) during the entire period of the experiment and the others three were: T4) 1 ETp for 5 weeks followed by 0.5 ETp for 4 weeks and 1 ETp for 5 weeks (strong deficit irrigation in phase II); T5) 1 ETp for 5 weeks followed by 0.25 ETp for 4 weeks and 1 ETp for 5 weeks (very strong deficit irrigation in phase II) and T6) 0.5 ETp for 5 weeks followed by 1 ETp for 4 weeks and 0.5 ETp for 5 weeks (strong deficit irrigation in phases I and III and well watered plants in phase II). The results showed that exposing plants to moderate water deficit (0.75 ETp) for 14 weeks had the best effect on quality of Rhododendron ‘Old Port’ plants. In this cultivar the application of very strong water deficit (0.25 ETp) for 4 weeks during floral buds initiation improved significantly floral bud set. Reduction of water supply by 50% during 14 weeks of Rhododendron ‘Catawbiense Boursault’ cultivation resulted in both the enhanced plant quality and increased number of floral buds set. Rhododendrons has adapted to reduced water supplies through stomatal control. At the end of the experiment, chlorophyll fluorescence parameter Fv/Fm (quantum efficiency of photosystem II) did not indicate damage to photosynthetic apparatus and relative chlorophyll content in leaves of plants subjected to all irrigation regimes did not differ significantly between each other.

<p>The aim of this study was to analyze the physiological and morphological response of <em>Syringa meyeri </em>‘Palibin’ to different levels of irrigation and to evaluate regulated deficit irrigation (RDI) as a possible technique for saving water in nursery production and promoting of flowering. Plants were grown in 3 liter containers in an unheated greenhouse and were subjected to six irrigation treatments for 18 weeks from the be- ginning of June to mid-October 2011. A drip irrigation system was used. Irrigation treatments were established on the basis of evapotranspiration (ETp). Three constant irrigation treatments were used: 1) 1 ETp; 2) 0.75 ETp; 3) 0.5 ETp, while the other three with irrigation varying between phases were as follows: 4) 1–0.5–1; 5) 1–0.25–1; and 6) 0.5–1–0.5 ETp. The 0.75 ETp and 0.5 ETp irrigation regimes adversely affected the growth and visual quality index of plants as well as they resulted in reduced leaf conductance, transpiration, maximum quantum efficiency of photosystem II (Fv/Fm) and CCI (chlorophyll content index). Plants grown under the 1–0.5–1 ETp regime had the same morphological parameters as plants grown under the 0.5 ETp treatment. A further reduction of water quantity supplied to plants in the 1–0.25–1 ETp regime resulted in further deterioration of the visual quality index of plants. In this study, the quality index of plants exposed to 0.5–1–0.5 ETp was similar to control plants (1 ETp). These plants were lower, more compact, and had smaller leaves than control plants. The irrigation regimes imposed in this study had no significant effect on the number of floral buds formed in relation to the control regime, except for 1–0.25–1 ETp where this number decreased.</p>