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M. Hossein Behboudian and Robert Lai

Responses of the tomato (Lycopersicon esculentum Mill. cv. Virosa) plant to elevated CO2 concentrations applied throughout the photoperiod or part of it were studied under two temperature regimes. Plants were exposed to CO2 at 340 (control), 700, and 1000 μl·liter–1. The highest concentration was applied only at 22/16C (day/night) and 700 μl·liter–1 at 22/16C and 25/16C. Transpiration rates were lower and photosynthetic rates were higher under elevated CO2 than at the ambient level. Biomass production was higher only for plants grown at 700 μl·liter–1 and 25/16C. Concentrations of macronutrients were lower in plants exposed to 1000 μl CO2/liter than in the control plants. Intermittent CO2 was applied using two timing methods. In method 1, plants were exposed to 4- or 8-hour high-CO2 concentrations during their 12-hour photoperiod. In method 2, plants were exposed for 3.5 days of each week to 700 μl CO2/liter. Only two of the 8-hour exposures resulted in greater growth than the controls. The lack of higher growth for CO2-enriched plants at 22/16C was attributed to a higher dark respiration rate and to a lack of efficient transport of photosynthates out of leaves.

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M. Hossein Behboudian and Colin Tod

The effect of preharvest CO2 enrichment (1000 μl·liter–1) on postharvest quality of tomato fruit (Lycopersicon esculentum Mill. `Virosa') was studied with an emphasis on soluble sugars, ripening, and mineral composition. High-CO2 fruit had higher concentrations of sucrose, glucose, fructose, and total soluble solids than ambient-CO2 fruit. High-CO2 fruit also ripened more slowly and was characterized by lower respiration and ethylene production rates than ambient-CO2 fruit. Concentrations of N, P, and K were lower in the high-CO2 fruit than in the ambient-CO2 fruit, whereas those of S, Ca, and Mg were the same for both treatments. Preharvest CO2 enrichment of `Virosa' tomato enhances fruit desirability in terms of slower postharvest ripening and higher concentrations of soluble sugars and total soluble solids.

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Tessa M. Mills, Jianming Li and M. Hossein Behboudian

Information on water relations and water stress physiology of Actinidia chinensis Planch. is scant. We aimed at providing such information by exposing potted 1-year-old plants to reduced irrigation in a glasshouse. The treatments were control (C) receiving sufficient water to replace 100% of evapotranspiration, early (E) reduced irrigation for 13 days earlier in the experiment, late (L) reduced irrigation for 13 days later in the experiment, and recovery (R) undergoing E and L with 5 days of full irrigation in between to recover from E. All plants were fully watered between early and late episodes of reduced irrigation. Soil volumetric water content was lower in E, L, and R compared with C, leading to lower leaf water potential, photosynthetic rate (Pn), and stomatal conductance (gs). Pn was lower in the reduced irrigation vines only when gs was below 0.1 mol·m−2·s−1. High leaf temperature in the glasshouse imposed nonstomatal limitations to photosynthesis as indicated by elevated internal leaf CO2 concentrations (Ci). Following rewatering, the stressed vines showed rapid recovery of leaf water potential and photosynthesis. However, Ci and gs were slower to respond. There was an indication of osmotic adjustment in leaves under reduced irrigation. Discrimination against 13CO2 was the same among the treatments. A. chinensis had better stomatal control under water stress compared with Actinidia deliciosa, for which some information is available. Water stress history in A. chinensis encouraged more drought resistance in the subsequent water stress period, but this was not sustained. Although field performance of A. chinensis under water stress is expected to be better than what we have presented here, long periods of deficit irrigation for this species cannot be recommended.

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Tessa M. Mills, M. Hossein Behboudian and Brent E. Clothier

Information on fruit water relations is scant for apple trees, especially under deficit irrigation. Here we discuss plant and fruit responses to deficit irrigation. Three-year-old potted `Braeburn' trees were studied in a glasshouse. The treatments were: well-watered control (C), early deficit (D1), and late deficit (D2). The latter two were, respectively, water stressed during 61–183 and 109–183 days after full bloom (DAFB). The final harvest was at 183 DAFB. Photosynthesis, stomatal conductance, and trunk circumference were lower in D1 and D2 than in C. Leaf area and shoot growth was reduced only in D1. Root length remained the same for all treatments. Fruit were smaller in D1 than in C; however, fruit growth was less sensitive to deficit irrigation than was vegetative growth. Fruit growth in D2 was the same as in C. Fruit concentrations of K+, fructose, sorbitol, total sugars, and titratable acidity were higher in D1 than in D2 and C. Total soluble solids were higher in D1 and D2 than in C. Although fruit water potential was lower in D1 than in C, a concomitant lowering of osmotic potential in D1 fruit led to maintenance of turgor potential, indicating osmotic adjustment. This could have been effected, at least partially, through accumulation of K+ and soluble sugars. Water relations of D2 fruit were not affected by deficit irrigation, although leaf water potential was lower than in C. Fruit water relations and fruit growth are therefore less sensitive to deficit irrigation than are those of vegetative parts.

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Horst W. Caspari, M. Hossein Behboudian and David J. Chalmers

Five-year old `Hosui' Asian pear (Pyrus serotina Rehder) trees growing in drainage lysimeters and trained onto a Tatura trellis were subjected to three different irrigation regimes. Weekly water use (WU) was calculated using the mass-balance approach. Soil-water content of control lysimeters was kept at pot capacity, while deficit irrigation was applied before [regulated deficit irrigation (RDI)] and during the period of rapid fruit growth [late deficit irrigation (LDI)]. Soil-water content was maintained at ≈50% and 75% of pot capacity for RDI and LDI, respectively. Deficit irrigation reduced mean WU during RDI and LDI by 20%. The reduced WU was caused by lower stomatal conductance (gs) on deficit-irrigated trees. RDI trees had more-negative diurnal leaf water potentials (ψl). The ψl, gs, and WU remained lower for 2 weeks after RDI was discontinued. RDI reduced shoot extension and summer pruning weights, whereas winter pruning weights were not different between treatments. Except for the final week of RDI, fruit growth was not reduced, and fruit from RDI grew faster than the control during the first week after RDI. In contrast, fruit volume measurements showed that fruit growth was clearly inhibited by LDI. Final fruit size and yield, however, were not different between treatments. Return bloom was reduced by RDI but was not affected by LDI.

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Lucio U. Pulupol, M. Hossein Behboudian and Keith J. Fisher

In glasshouse-grown tomatoes (Lycopersicon esculentum Mill. `Virosa'), deficit irrigation (DI), in which plant water potential was allowed to decrease from –0.5 to –1.2 MPa, reduced plant growth and fruit yield, size and count, and caused blossom-end rot. Deficit-irrigated fruit had higher color intensity, lower water content, and higher concentration of sucrose, glucose, and fructose than well-watered (control) fruit. Fruit concentrations of Ca, Mg, and K were the same for both treatments on a dry weight basis, but they were higher in DI fruit than in control fruit on a fresh weight basis. Fruit gas exchange was measured for two 30-day-apart harvests. For both harvests, DI fruit produced higher quantities of CO2 and ethylene than control fruit. Ethylene and CO2 production peaks coincided for the first harvest in both treatments. In the second harvest, the CO2 production peak preceded that of ethylene. Despite yield reduction, DI enhanced fruit desirability in terms of higher concentration of soluble sugars and higher color intensity.

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Horst W. Caspari, M. Hossein Behboudian, David J. Chalmers, Brent E. Clothier and Fritz Lenz

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Xavier Vallverdu, Joan Girona, Gemma Echeverria, Jordi Marsal, M. Hossein Behboudian and Gerardo Lopez

Deficit irrigation (DI) applied during Stage II of fruit development has the potential of improving fruit quality in peach (Prunus persica). Existing information only covers instrumental assessment of quality. No report is available on how sensory attributes and consumer acceptance are affected. We applied DI at Stage II to ‘Tardibelle’ peach and evaluated fruit composition, sensory attributes, and consumer acceptance during the growing seasons of 2009 and 2010. Results were compared with those from trees that received conventional irrigation (CI). Stem water potential in DI trees was indicative of a moderate water stress during Stage II. In 2010, water stress persisted at the beginning of Stage III and average fruit weight was reduced in DI trees. A panel of trained judges decided that DI increased sweetness, juiciness, and the intensity of peach flavor but it reduced fruit firmness and crispness. A panel of consumers indicated increased preference for DI fruit. The higher appeal for DI fruit could have been partially the result of their more advanced maturity. Improvement of fruit quality could be an important incentive for the application of DI during Stage II because growers may expect to receive a premium price for their higher quality fruit.

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Jorge A. Zegbe, M. Hossein Behboudian, Brent E. Clothier and Alexander Lang

Quality and storability of ‘Pacific Rose™’ apple grown under partial rootzone drying (PRD) were studied over 2 years. The treatments were commercial irrigation (CI) and PRD, which were applied by watering one side of the tree row throughout the season (Expt. 1) or by alternating irrigation between two sides of the tree row when volumetric soil water content ranged between 0.18 and 0.22 m3·m−3 (Expt. 2). The PRD and CI fruit had similar quality attributes at harvest and after storage except that the former had lower weight loss during storage in Exp. 1 and a lower firmness after storage in Exp. 2. Compared with CI, PRD saved water by 0.15 mega liters per hectare in Exp. 1 and by 0.14 mega liters per hectare in Exp. 2. We recommend PRD for humid environments similar to ours.

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Gerardo Lopez, M. Hossein Behboudian, Gemma Echeverria, Joan Girona and Jordi Marsal

The dwindling water supply, on a global scale, is making deficit irrigation (DI) more a necessity than a choice. It is therefore necessary to evaluate the effects of DI on fruit quality. Only instrumental evaluation of quality has been reported in the literature and, to the best of our knowledge, no sensory evaluation has been reported for any DI fruit including peach (Prunus persica). We applied four irrigation treatments for 50 days before harvest to ‘Ryan's Sun’ peach and evaluated fruit quality and sensory attributes. Treatments were: full irrigation (FI), no irrigation (NI), FI followed by NI (FI/NI), and NI followed by FI (NI/FI). NI reduced fruit size, delayed fruit maturity, and increased fruit dry matter concentration (DMC) compared with FI. NI also increased fruit soluble solids concentration (SSC) and titratable acidity (TA). A trained taste panel indicated that NI increased fruit firmness, crispness, and sourness, but it reduced sweetness, juiciness, and the intensity of peach flavor. A panel of consumers indicated reduced preference for NI fruit. Consumer preference was similar between NI/FI and FI fruit but was reduced in FI/NI fruit. There were no significant correlations between the instrumental quality parameters and sensory attributes. We conclude that NI before harvest impaired organoleptic peach quality. If only a small amount of water is available during the 50 days before harvest, peach organoleptic quality could be improved if this water is applied just before harvest.