effect of water stress on growth characteristics and gas exchange in paclobutrazol - treated pear (pyrus communis cv. bairouty )

paclobutrazol was utilized to analyze its role in water stress amelioration and post drought recovery of container-grown pear ( pyrus communis cv. biroti ) saplings. following planting, paclobutrazol was applied as soil drench at concentration of 0, 0.15 and 0.3 mg per pot. three months following planting, saplings were subjected to three water stress treatments of: 0, -0.4 and -0.8 mpa. control treatment was subjected to daily irrigation. irrigation was applied when soil water potential reached -0.4 and -0.8 for the water stress treatments. all traits were recorded during water stress as well as two day following rewatering. results showed that paclobutrazol effectively slowed down growth parameters. paclobutrazol decreased saplings, growth, mean leaf area, trunck diameter, shoot and plant dry weights. but, significant differences were not observed between 0.15 and 0.3 gr/pot paclobutrazol treatments. paclobutrazol did not affect membrane stability index. leaf chlorophyll (a, b and total) contents were affected by paclobutrazol and water stress treatments, but their interaction was not significant. total leaf chlorophyll content was higher in 0.15 and in 0.3 gr/pot paclobutrazol treatments than in control. leaf proline (73.4 µmol/gr dry weight) and total carbohydrate (2.35 gr/100 gr dry weight) contents were recorded as the highest in -0.8 mpa water stress treatment. photosynthesis rate, stomatal conductance and transpiration (4.59 molm-2s-1( were recorded as least in -0.8 mpa water stress treatment. these parameters were identical at the beginning of water stress treatment and withing two days after rewatering. when compared with non-paclobutrazol-treated controls, paclobutrazol treatments contained higher sub-stomatal co2. in conclusion, the results showed that paclobutrazol induces more water stress tolerance in pear (cv. biroty) by affecting the vegetative, biochemical and gas exchange traits.