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Introduction . Fruit production is faced with water shortage, especially in areas with a Mediterranean climate characterized by a very long, dry and hot summer. Thus, the growers under such conditions must manage irrigation carefully by finding new strategies, including water stress management. Materials and methods . Effects of water stress (WS) and crop load (CL) on the carbon assimilation rate, fruit growth, crop yield and fruit quality (size and soluble solids content) were evaluated in a 7-year-old ‘Elegant Lady’ peach orchard (Winters, California, USA). The experimental design consisted of a completely randomized block factorial design with 2 × 3 factors: irrigation with two levels (control and WS trees) and crop load with three levels (light, commercial and heavy). Results and discussion . Both CL and WS affected fruit growth during the last stages but not early on. Crop load did not affect trunk water potential (TrWP) which, however, was significantly reduced by WS throughout the day and the season. The stomatal conductance (gs ), transpiration rate (E) and CO2 assimilation rate (A) were not affected by CL, but they were reduced by WS. There were poor correlations between TrWP and either gs or A in control trees, indicating relatively poor coordination between leaf functions in peach trees under optimal conditions. Both WS and CL delayed the harvest date through their effect on ripening. Water stress significantly reduced the average crop fresh yield but hardly affected crop dry yield. Both WS and CL affected the distribution of fruit size categories, with the proportion of large fruit decreasing with the increase in crop load and the severity of WS. Conclusion . Water stress reduced fruit fresh weight and fruit fresh yield but not fruit dry weight or dry yield. Crop load reduced fruit fresh and dry weights and yields. Crop load had a negative effect on soluble solids content, while WS had a positive effect. Thus, CL reduced fruit size and soluble solids content, while WS reduced size but improved soluble solids concentration.

Introduction . Vegetative and fruit growth in fruit trees are differentially sensitive to water deficit during the season depending on the stage of fruit growth. Attempts have been made to evaluate the possibilities of using regulated deficit irrigation to control vegetative growth and save water in the fruit industry. Materials and methods . Effects of water stress (WS) and crop load (CL) on fruit growth and carbon assimilation rates were evaluated in a 7-year-old ‘Elegant Lady’ peach orchard. A completely randomized block design with 2 × 3 factors [irrigation with two levels (control and WS) and CL with three levels (light, commercial and heavy)] was used. Results and discussion . Both WS and CL affected fruit growth during the last stages but not early on. CL did not affect trunk water potential which was, however, significantly reduced by WS throughout the day and the season. Trunk water potential of water-stressed trees was lower than that of control trees throughout the day and the season regardless of CL. The magnitude of WS increased as the season progressed. Stomatal conductance, transpiration rate and CO2 assimilation rate were not affected by CL but were reduced by WS. The trees responded (acclimated) to stress by progressively reducing their transpiration rate as the severity of stress increased. For each irrigation regime, assimilation rates were similar for all three crop levels. This indicated the existence of alternate sinks for assimilates when CL was low, which compensate for the reduction of fruit sink activity resulting from fruit thinning. Conclusion . Water deficit reduced trunk water potential, stomatal conductance, transpiration and photosynthesis in ‘Elegant Lady’ peach trees. However, CL had a limited effect on these functions. There were good correlations between trunk water potential and either stomatal conductance or assimilation rate in water-stressed trees but not in control trees. This indicates a poor coordination between leaf functions in peach trees under optimal conditions. However, these relationships were stronger under WS conditions. Thus, water use efficiency appeared to increase under water deficit conditions.

Among woody plants, grapevines are often described as highly vulnerable to water-stress induced cavitation with emboli forming at slight tensions. However, we found native embolism never exceeded 30% despite low xylem water potentials (Psi(x)) for stems of field grown vines. The discrepancy between native embolism measurements and those of previous reports led us to assess vulnerability curve generation using four separate methods and alterations (i.e. segment length and with/without flushing to remove embolism prior to measurement) of each. Centrifuge, dehydration and air-injection methods, which rely on measurement of percentage loss of hydraulic conductivity (PLC) in detached stems, were compared against non-invasive monitoring of xylem cavitation with nuclear magnetic resonance (NMR) imaging. Short segment air-injection and flushed centrifuge stems reached90 PLC at Psi(x) of-0.5 and -1.5 MPa, respectively, whereas dehydration and long-segment air-injection measurements indicated no significant embolism at Psi(x)-2.0 MPa. Observations from NMR agreed with the dehydration and long segment air-injection methods, showing the majority of vessels were still water-filled at Psi(x)-1.5 MPa. Our findings show V. vinifera stems are far less vulnerable to water stress-induced cavitation than previously reported, and dehydration and long segment air-injection techniques are more appropriate for long-vesseled species and organs.