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Luis R. Valenzuela, Denise Neilsen, Gerry Neilsen, and David Eissenstat

New irrigation practices using controlled soil water deficits offer the opportunity of reducing tree vegetative growth and enhancing fruit quality without decreasing fruit size or yield. We tested partial root zone drying (PRD) and deficit irrigation in `Golden Delicious' trees on M9 rootstock, at Summerland, B.C., Canada. There were four treatments: full irrigation (100% daily ET replacement), both sides irrigation (50%daily ET replacement), deficit irrigation (1 side, 50% daily ET replacement) and PRD (alternating sides, 50% daily ET replacement). The purpose of this study was to determine how deficit irrigation and PRD affect above- and below-ground physiology of apple trees where the amount of irrigation was the same. Soil water content, stem water potential, stomatal conductance and transpiration were significantly higher for deficit irrigation than PRD irrigation (P < 0.05) for both years (2003 and 2004). Root dynamics varied among years. For both years, root production was higher in trees under PRD than in trees under deficit irrigation. Root survivorship was significantly higher for trees exposed to PRD treatment than those exposed to deficit irrigation treatment in 2003 (P < 0.0003), but not in 2004 (P > 0.662). Stem growth, fruit yield, and fruit quality were generally not affected by treatments in 2003. In 2004, however, fruit yield was 37% higher in deficit irrigation than in PRD (P < 0.05). Soluble solids and sugar: acid ratio did not differ between these two treatments. For conditions where the amount of irrigation applied was the same, our results suggest that PRD may be less effective than deficit irrigation.

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Li-Juan Zhang, Tian-Xiu Zhong, Li-Xin Xu, Lie-bao Han, and Xunzhong Zhang

Soil water deficit impacts cold acclimation and freezing tolerance in creeping bentgrass (Agrostis stolonifera L.), but the mechanisms underlying have not been well understood. The objectives of this study were to investigate the effects of deficit irrigation before and during cold acclimation on osmoprotectants, antioxidant metabolism, and freezing tolerance in creeping bentgrass. The grass was subjected to three-soil moisture levels: well-watered [100% container capacity (CC)], deficit irrigation induced-mild drought stress (60% CC), and severe drought stress (30% CC) for 35 days including 14 days at 24/20 °C (day/night) and then 21 days under cold acclimation treatment (2 °C) in growth chambers. Leaf proline and total soluble sugar (TSS) levels were higher in the grass under mild drought stress relative to that under severe drought stress. Superoxide (O2 −·), hydrogen peroxide (H2O2), and malondialdehyde (MDA) content were higher in the grass under severe drought relative to that under well-watered and mild drought stress at day 35. Mild drought stress increased catalase (CAT) and guaiacol peroxidase (POD) activity, induced new isoforms and increased band intensities of superoxide dismutase (SOD), CAT, and POD during cold acclimation (days 14 to 35). No differences in osmoprotectants, antioxidant metabolism, and freezing tolerance were found between mild drought and well-watered treatments. The results of this study suggest deficit irrigation-induced mild drought stress in late fall and winter could induce accumulation of osmoprotectants and improve antioxidant metabolism, and freezing tolerance, but severe drought stress could reduce freezing tolerance of creeping bentgrass in the region with limited precipitation.

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Jordi Marsal and Joan Girona

Relationships between midday (Ψmd) and predawn (Ψpd) leaf water potential, stomatal conductance (gs), and net CO2 assimilation rate (A) were determined at different fruit growth stages and for 2 years with different fruit loads in a `Sudanell' peach [Prunus persica (L) Batsch] plot subjected to two regulated deficit irrigation (RDI) strategies plus a control irrigation treatment. A postharvest RDI (PRDI) treatment was irrigated at 0.35 of the control after harvest. The second treatment (SPRDI) applied RDI during Stage II, the lag phase of the fruit growth curve, at 0.5 of the control and postharvest at 0.35 of the control. The control treatment and the PRDI and SPRDI when not receiving RDI were irrigated at 100% of a modified Penman crop water use calculation (ETo) in 1994, a full crop year, and 80% in 1995, a year of nearly zero crop. In 1995, with 80% of the 1994 irrigation rate and no crop, the Ψmd was higher, probably because of the lower crop load, while Ψpd was lower, probably because less water was applied to the soil. The relationship of gs and A with Ψmd during Stage II was steeper than during postharvest. Low Ψmd was not indicative of a depression in gs and A in Stage III. Osmotic leaf water potential at turgor loss (Ψπ 0) as derived from pressure-volume curves was more negative during Stage III and postharvest (about -2.9 MPa) than in Stage II (about -2.7 MPa). The Ψmd measurements together with Ψπ 0 determinations seemed to be more useful to characterize peach tree water status than Ψpd under soil water deficits because of their better relationship to midday stomatal closure.

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Khalid F. Almutairi, David R. Bryla, and Bernadine C. Strik

water-limited conditions. Thus, research is needed to determine whether there is any value to crop thinning during soil water deficits in blueberry. The objective of the present study was to evaluate the potential of using deficit irrigation, irrigation

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Zhiyong Wang, Paul Raymer, and Zhenbang Chen

potassium HortScience 46 1400 1403 Cathey, S.E. Kruse, J.K. Sinclair, J.K. Dukes, M.D. 2011 Tolerance of three warm-season turf grasses to increasing and prolonged soil water deficit HortScience 46 1550 1555 Chen, S.L. Phillips, S.M. 2006 The flora of China

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Karl Guillard and John C. Inguagiato

-season turfgrasses to increasing and prolonged soil water deficit HortScience 46 1550 1555 Doak, S.O. Schmidt, R.E. Ervin, E.H. 2005 Metabolic enhancer impact on creeping bentgrass leaf sodium and physiology under salinity Intl. Turfgrass Soc. Res. J. 10 845 849

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Juan Carlos Díaz-Pérez and Touria E. Eaton

.027), suggesting that marketable yield was determined more by fruit number than individual fruit weight. In greenhouse-grown eggplant, soil water deficit decreased fruit number but not fruit size ( Chartzoulakis and Drosos, 1995 ). In a study with different levels

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Ana Centeno, Pilar Baeza, and José Ramón Lissarrague

June). In practical terms, vines grow throughout the season under controlled water deficit to prevent severe water stress. Soil water deficit reduces vegetative growth ( Deloire et al., 2004 ; Intrigliolo and Castel, 2006 ; Matthews et al., 1987

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Xuelian Jiang, Yueling Zhao, Ling Tong, Rui Wang, and Sheng Zhao

), soil water deficit ( Patanè and Cosentino, 2010 ), and seasonal irrigation volume ( Favati et al., 2009 ; Kuscu et al., 2014 ; Zheng et al., 2013 ). There are many studies of the relationship between yield and water deficit but few studies that

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Xuelian Jiang, Yueling Zhao, Rui Wang, and Sheng Zhao

priorities and future directions Ann. Appl. Biol. 147 211 226 Patanè, C. Cosentino, S.L. 2010 Effects of soil water deficit on yield and quality of processing tomato under a Mediterranean climate Agr. Water Mgt. 97 131 138 Patanè, C. Tringali, S. Sortino, O