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Jennifer R. DeEll and Geoffrey B. Lum

Both, V. Thewes, F.R. Brackmann, A. Ferreira, D.D.F. Pavanello, E.P. Wagner, R. 2016 Effect of low oxygen conditioning and ultralow oxygen storage on the volatile profile, ethylene production and respiration rate of ‘Royal Gala’ apples Sci. Hort. 209

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Juan Pablo Zoffoli, Valentina Sanguedolce, Paulina Naranjo, and Carolina Contreras

oxygen (ULO; 0.7 kPa O 2 ), a controlled atmosphere (CA) storage technology which reduces superficial scald ( Wang and Dilley, 2000 ) and its variants initial low oxygen (ILO) ( Wang and Dilley, 1999 ; Zanella, 2003 ) and dynamic atmosphere storage (DCA

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Gustavo H.A. Teixeira and José F. Durigan

storage ( Azzolini et al., 2004 ). With the delayed ripening process observed for fruits stored at low oxygen levels (1 and 5 kPa), namely, reduced respiration rates and firmness retention, these fruits were not appropriate for consumption right after

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Hisashi Kato-Novuchi and Alley E. Watada

Carrot (Daucus carota L.) shreds were stored under a continuous flow of 0.5% O2 (balance N2), 2% O2 (balance N2), or air for 9 days at 5C and 15C. The resulting changes in respiration and levels of the glycolytic intermediates were monitored. Low-oxygen atmosphere reduced respiration rate, but the RQ increased. The RQ was higher at 0.5% O2 than at 2% O2 atmosphere at both 5C and 15C. The most significant change in the levels of glycolytic intermediates was the accumulation of fructose 1,6-biphosphate. The level of fructose 1,6-biphosphate at 0.5% O2 was about 2-fold greater than at 2% O2 atmosphere at both 5C and 15C. The level of the other glycolytic intermediates at low-oxygen atmosphere was similar to that held in air atmosphere. These results suggest that phosphofructokinase activity in the tissue of carrots may increase under low-oxygen condition and it may be one of the controlling points in the glycolytic pathway affected by low oxygen concentrations.

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Krista C. Shellie and Ken Rodde

A treatment schedule for disinfesting grapefruit of Mexican fruit fly with refrigerated (14 °C) storage for 21 days in ultra-low oxygen (0.05 kPa) was tested using a fully loaded, 24-ft sea freight container. The objective of this research was 3-fold: 1) evaluate the ability of a free standing Electronic Oxygen Control system to maintain 500 ppm of oxygen for 21 days inside the sealed container, 2) evaluate the mortality of third instar Mexican fruit fly larvae stored for 21 days inside the sealed container, and 3) evaluate fruit market quality after 21 days inside the container. The container was loaded with 17 pallets of red-fleshed, `Rio Star' grapefruit. Three boxes from each pallet were evaluated for fruit quality (decay (%), visible disorders (%)) after 21 days of treatment and again after 14 additional days of storage in air at 10 °C. Four cartons, each containing 24 fruit infested with third instar, Mexican fruit fly larvae, were each placed on top of a pallet in four different container locations. Upon completion of treatment, larvae were evaluated for survival. In the first replication, no fruit fly larvae survived the low oxygen treatment. In the second replication, oxygen concentration was less controlled, and 60 pupae survived the treatment. Treated and control grapefruit had similar incidence of decay when the treatment was terminated, however no sporulation was observed in fruit stored under ultra-low oxygen. Grapefruit exposed to ultra-low oxygen had a higher incidence of visible disorders, consisting of darkened, sunken areas on the fruit surface. It is unclear whether this damage is attributed to fluctuating levels of oxygen, deleterious volatiles produced during treatment, or a sensitivity of the fruit to low oxygen.

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Heidi A. Kratsch* and William R. Graves

Alnus maritima (Marsh.) Muhl. ex Nutt. is unique among alders in its degree of preference for low-oxygen soils of wetlands. An actinorhizal species with promise for use in sustainable horticulture, A. maritima develops a root-nodule symbiosis with nitrogen-fixing Frankia. Nodules of other actinorhizal species that are obligate wetland natives are adapted to low oxygen, and expression of hemoglobin is common to these taxa. Our objectives were to determine the range of oxygen tension under which Alnus maritima subsp. maritima fixes nitrogen and to investigate a potential role for hemoglobin in adaptation of nodules to low oxygen. Roots of plants, cultured aeroponically, were subjected to eight oxygen tensions from 0 to 32 kPa. After four weeks, plant dry weight, nodule fresh weight, nitrogenase activity, and photosynthetic rate were measured. In addition, nodules were assayed spectrophotometrically for the presence of hemoglobin. A quadratic function best described the influence of oxygen on plant dry weight, nodule fresh weight, nitrogenase activity, and photosynthetic rate with maximal values above 20 kPa. Alnus serrulata (Ait.) Willd. is sympatric with A. maritima subsp. maritima but is not an obligate inhabitant of wetlands. In a separate experiment, we found higher nitrogenase activity in A. maritima subsp. maritima than in A. serrulata (0.74 vs. 0.26 μmol/h per plant) at hypoxic oxygen tensions. Further, optical absorption spectra of nodule extracts confirmed hemoglobin within nodules of A. maritima subsp. maritima. Our data suggest that hemoglobin contributes to oxygen regulation in nodules of A. maritima subsp. maritima.

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Randolph M. Beaudry

The application of low oxygen through modified atmosphere packaging (MAP) is a technique used successfully to preserve the visual quality of lettuce and some other commodities. The expansion of use of low O2 via MAP to preserve quality of most commodities is limited by technical difficulties achieving target O2 concentrations, adverse physiological responses to low O2, and lack of beneficial responses to low O2. Low O2 often is not used simply because the physiological responses governed by the gas are not limiting quality maintenance. For instance, shelf life may be governed by decay susceptibility, which is largely unaffected by low O2 and may actually be exacerbated by the conditions encountered in hermetically sealed packages. Physiological processes influenced by low O2 and limit storability are discussed. The interdependence of O2 concentration, O2 uptake by the product, and temperature are discussed relative to requirements for packaging films.

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Gary F. Polking, Richard J. Gladon, and David S. Koranski

Generation of pregerminated seeds at a central facility and subsequent mechanical sowing at a remote facility require that radicle elongation during shipment be minimized. Low-oxygen treatments were applied to pregerminated `Super Elfin Salmon Blush' impatiens seeds to suppress radicle growth during a subsequent one-day simulated shipping period in air. In the first experiment, O2 concentrations of 0, 3, 7, 10, 13, and 20% were applied for 24 and 48hr. The 0% O2/24-hr and the 0% O2/48-hr treatments held the radicle length close to the desired length of 1.0mm, but both of these treatments decreasad 7-day hypocotyl length and percentage normal seedlings, when they were compared with the control treatment (untreated pregerminated seeds) In the second experiment, O2 concentrations of 0, 1, 2, 3, 7, and 20% were applied for 24 and 48hr. Five treatments (0, 1, and 2% O2/24-hr and 0 and 1% O2/48-hr) held the radicle to a length <1.0mm. Of these five treatments, only the 2% O2/24-hr treatment resulted in recovery parameters (7-day hypocotyl length and percentage normal seedlings) that compared with those of the control treatment.

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Mary E. Mangrich and Mikal E. Saltveit

Crops with origins in tropics and subtropics undergo physiological injury when subjected to nonfreezing temperatures below 12°C. Application of heat and chemical shocks to tissue prior to chilling induces chilling tolerance. This study was undertaken to investigate the effects of low oxygen and high carbon dioxide atmospheres on subsequent chilling tolerance. Cucumber seedlings (Cucumis sativus L., cv. Poinsett 76) with radicles 8 to 12 mm long were subjected to 0% to 21% oxygen and/or 0% to 20% CO2 atmospheres for 0 to 72 hr at 2.5 or 15°C. After chilling, they were placed at 25°C for three additional days. Radicle growth was used to assess chilling injury. Modification of the individual germination plates was necessary to ensure seedling exposure to the desired atmospheres. Chilling injury was reduced by exposure to oxygen levels below 1% and to carbon dioxide levels above 5%. Effects of brief exposures were small in comparison to prolonged exposures during chilling. Seed to seed variability was high and obscured some results. The effects of the various atmospheres were greater with the less vigorous seedlings.

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Abd. Shukor Rahman

Controlled-atmosphere (CA) storage of fruits employing low O2 and/or elevated CO2 have been used to reduce respiration and other associated metabolic activities. Papaya fruit cv. Eksofika were exposed to 2%, 5%, and 21% (air) O2 for 4 weeks at 12C. The CO2 production rates of fruit previously stored in 2% and 5% O2 were suppressed during storage, but increased upon transfer to air at 20C. Carbon dioxide production rates of low-oxygen stored fruits were slightly lower than the air-stored fruit during transfer to air, indicating a slight residual effect of low O2 on the respiratory activity of the fruit. This was highly evident in fruit stored in 2% O2 for 4 weeks. Ethylene production rates were not affected by prior storage of fruit in low-O2 atmosphere. Anaerobic metabolism did not occur in fruit stored in 2% O2 for 4 weeks, as evidenced by the RQ values close to unity and the absence of ethanol from the headspace of the respired gas. The total sugar content of ripe fruit at color score 5, previously stored in low-O2 atmosphere for 4 weeks, were not significantly different from the air-stored fruit.