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  • Author or Editor: Arthur C. Cameron x
  • Journal of the American Society for Horticultural Science x
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In one set of modified-atmosphere (MA) packages of cut broccoli (Brassica oleracea L., Italica Group), O2 partial pressures ranged from 1.2 to 3.6 kPa at 0C [88 packages, 0.00268-cm-thick low-density polyethylene (LDPE) film, 600-cm2 film area, 40±0.5 g cut broccoli], and in another set (94 packages, same film and area as before, 25±0.5 g cut broccoli) they ranged from 5.0 to 9.2 kPa. For characterizing O2 uptake as a function of O2 partial pressure and determining anaerobic fermentation induction point at 0C, a range of steady-state package O2 partial pressures was generated by placing different amounts of cut broccoli (10 to 160 g) in LDPE packages. Oxygen uptake was modeled using a Michaelis-Menten-type equation. The maximum rate of product O2 uptake when O2 partial pressure was nonlimiting and the package O2 partial pressure corresponding to half-maximum O2 uptake were estimated as 147±3 nmol·kg-1·s-1 and 0.26±0.025 kPa, respectively. Respiratory quotient and head space ethanol increased sharply below package O2 partial pressures of 0.15 kPa, indicating stimulation of fermentation within the packages. The frequency distributions of CO2 production rates were measured for 80 samples of 100 g each of cut broccoli at two O2 partial pressures (21.0 kPa and 1.3 kPa) using a flow-through method. The average coefficient of variation of the CO2 production rate was ≈5%. Frequency distributions of O2 partial pressures were modeled as a function of product-to-product variation in O2 uptake and package-to-package variation in film permeability using the estimated O2 uptake characteristics and coefficient of variation. The model was used to predict the target O2 partial pressures for the design of cut broccoli MA packages. It was predicted that the packages for cut broccoli at 0C should be designed for a target O2 partial pressure of 2.54 kPa to have actual package O2 partial pressures ≥1.0 kPa at 0.0001% probability level. Film specifications for MA packaging of cut broccoli at 0C were calculated based on the predicted target O2 partial pressures.

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A mathematical model was developed to characterize the interaction of fruit O2 uptake, steady-state O2 partial pressures in modified-atmosphere (MA) packages ([O2]pkg), and film permeability to O2 (Po 2) from previously published data for highbush blueberry (Vaccinium corymbosum L. `Bluecrop') fruit held between 0 and 25C. O2 uptake in nonlimiting O2 (Ro 2 max,T) and the [O2]pkg at which O2 uptake was half-maximal (K½ T) were both exponentially related to temperature. The activation energy of 02 uptake was less at lower [O2]pkg and temperature. The predicted activation energy for permeation of O2 through the film ( \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{E}_{\mathrm{a}}^{\mathrm{P_{\mathrm{o}_{2}}}}\) \end{document} kJ·mol-1) required to maintain close-to-optimum [O2]pkg across the range of temperatures between 0 and 25C was ≈ 60 kJ·mol-1. Packages in which diffusion was mediated through polypropylene or polyethylene would have values \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{E}_{\mathrm{a}}^{\mathrm{P_{\mathrm{o}_{2}}}}\) \end{document} of ≈ 50 and 40 kJ·mol-1, respectively, and would have correspondingly greater tendencies for [O2]pkg to decrease to excessively low levels with an increase in temperature. Packages that depend on pores for permeation would have an \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{E}_{\mathrm{a}}^{\mathrm{P_{\mathrm{o}_{2}}}}\) \end{document} of <5 kJ·mol-1. Our procedure predicted that, if allowed to attain steady-state conditions, packages with pores and optimized to 2 kPa O2 at 0C would become anaerobic with as little as a 5C increase in temperature. The results are discussed in relation to the risk of temperature abuse during handling and marketing of MA packaged fruit and strategies to avoid induction of anaerobiosis.

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The effectiveness of cool-white fluorescent, high-pressure sodium, incandescent, and metal halide lamps for inducing flowering through daylength extensions in Campanula carpatica Jacq. `Blue Clips', Coreopsis grandiflora Hogg ex Sweet `Early Sunrise', and Coreopsis verticillata L. `Moonbeam' was compared. Lighting was delivered as a 7-hour day extension with photosynthetic photon flux (PPF) ranging from 0.05 to 2.0 μmol·m-2·s-1 following a 9-hour natural daylength. Threshold irradiance values for flowering ranged from <0.05 to 0.4 μmol·m-2·s-1, depending on species. Saturation irradiance values for Campanula carpatica `Blue Clips' and C. grandiflora `Early Sunrise' were between 0.2 ± 0.2 and 0.7 ± 0.5 μmol·m-2·s-1, and did not differ between lamps. An irradiance of 1.0 μmol·m-2·s-1 from any lamp was adequate for flowering in Coreopsis verticillata `Moonbeam'. Time to flower at irradiances above the saturation points did not differ significantly between lamp types for all species tested. Campanula carpatica `Blue Clips' and Coreopsis grandiflora `Early Sunrise' plants had significantly longer stems under incandescent lamps than in any other treatment. Coreopsis verticillata `Moonbeam' plants grown under cool-white fluorescent lamps had stems ≈10% longer than those grown under high-pressure sodium or incandescent lamps.

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Pansy [Viola ×wittrockiana Gams. `Delta Yellow Blotch' (Yellow) and `Delta Primrose Blotch' (Primrose)] plants were grown in a greenhouse under two CO2 concentrations [ambient (≈400 μmol·mol-1) and enriched (≈600 μmol·mol-1)], three daily light integrals (DLI; 4.1, 10.6, and 15.6 mol·m-2·d-1), and nine combinations of day and night temperatures created by moving plants every 12 h among three temperatures (15, 20, and 25 °C). Time to flower decreased and rate of flower development increased as plant average daily temperature (ADT) increased at all DLIs for Yellow or at high and medium DLIs for Primrose. Increasing the DLI from 4.1 to 10.6 mol·m-2·d-1 also decreased time to flower by 4 and 12 days for Yellow and Primrose, respectively. Both cultivars' flower size and Yellow's dry weight [(DW); shoot, flower bud, and total] decreased linearly as plant ADT increased at high and medium DLIs, regardless of how temperature was delivered during day and night. DW in Yellow increased 50% to 100% when DLI increased from 4.1 to 10.6 mol·m-2·d-1 under both CO2 concentrations. Flower size in Yellow and Primrose increased 25% under both CO2 conditions as DLI increased from 4.1 to 10.6 mol·m-2·d-1, but there was no increase between 10.6 and 15.6 mol·m-2·d-1, regardless of CO2 concentration. Plant height and flower peduncle length in Yellow increased linearly as the difference between day and night temperatures (DIF) increased; the increase was larger under lower than higher DLIs. The ratio of leaf length to width (LL/LW) and petiole length in Yellow increased as DIF increased at medium and low DLIs. Carbon dioxide enrichment increased flower size by 4% to 10% and DW by 10% to 30% except for that of the shoot at medium DLI, but did not affect flower developmental rate or morphology. DW of vegetative and reproductive parts of the plant was correlated closely with photothermal ratio, a parameter that describes the combined effect of temperature and light.

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`Heritage' raspberries (Rubus idaeus L.) were sealed in low-density polyethylene packages and stored at 0, 10, and 20C during Fall 1990 and 1991 to study respiratory responses under modified atmospheres. A range of steady-state O2 and CO2 partial pressures were achieved by varying fruit weight in packages of a specific surface area and film thickness. Film permeability to O2 and CO2 was measured and combined with surface area and film thickness to estimate total package permeability. Rates of O2 uptake and CO2 production and respiratory quotient (RQ) were calculated using steady-state O2 and CO2 partial pressures, total package permeability, and fruit weight. The O2 uptake rate decreased with decreasing O2 partial pressure over the range of partial pressure studied. The Michaelis-Menten equation was used to model O2 uptake as a function of O2 partial pressure and temperature. The apparent Km(K½) remained constant (5.6 kPa O2 with temperature, while Q10 was estimated to be 1.9. RQ was modeled as a function of O2 partial pressure and temperature. Headspace ethanol increased at RQs >1.3 to 1.5. Based on RQ, ethanol production, and flavor, we recommend that raspberries be stored at O2 levels above 4 kPa at 0C, 6 kPa at 10C, and 8 kPa at 20C. Steady-state CO2 partial pressures of 3 to 17 kPa had little or no effect on O2 uptake or headspace ethanol partial pressures at 20C.

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Highbush blueberry (Vaccinium corymbosum L. `Bluecrop') fruit sealed in low-density polyethylene packages were incubated at 0, 5, 10, 15, 20, or 25C until O2 and CO2 levels in the package reached a steady state. A range of steady-state O2 partial pressures (1 to 18 kPa) was created by placing a range of fruit weights within packages having a constant surface area and film thickness. The steady-state O2 partial pressure in packages containing the same weight of fruit decreased as temperature increased, indicating the respiratory rate rose more rapidly (i.e., had a greater sensitivity to temperature) than O2 transmission through the film. Steady-state O2 and CO2 partial pressures were used to calculate rates of O2 uptake. CO2 Production. and the respiratory quotient (RO). The effects of temperature and 02 partial pressure on O2 uptake and CO2 production and the RQ were characte∼zed. The steady-state O, partial pressure at which the fruit began to exhibit anaerobic CO2 production (the RQ breakpoint) increased with increasing temperature, which implies that blueberry fruit can be stored at lower O2 partial pressures when stored at lower temperatures.

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Influences of vernalization duration, photoperiod, forcing temperature, and plant growth regulators (PGRs) on growth and development of Oenothera fruticosa L. `Youngii-lapsley' (`Youngii-lapsley' sundrops) were determined. Young plants were vernalized at 5 °C for 0, 3, 6, 9, 12, or 15 weeks under a 9-hour photoperiod and subsequently forced in a 20 °C greenhouse under a 16-hour photoperiod. Only one plant in 2 years flowered without vernalization, while all plants flowered after receiving a vernalization treatment, regardless of its duration. Thus, O. fruticosa had a nearly obligate vernalization requirement. Time to visible bud and flower decreased by ≈1 week as vernalization duration increased from 3 to 15 weeks. All plants flowered under 10-, 12-, 13-, 14-, 16-, or 24-hour photoperiods or a 4-hour night interruption (NI) in a 20 °C greenhouse following 15-weeks vernalization at 5 °C. Time to flower decreased by ≈2 weeks, flower number decreased, and plant height increased as photoperiod increased from 10 to 16 hours. Days to flower, number of new nodes, and flower number under 24 hour and NI were similar to that of plants grown under a 16-hour photoperiod. In a separate study, plants were vernalized for 15 weeks and then forced under a 16-h photoperiod at 15.2, 18.2, 20.6, 23.8, 26.8, or 29.8 °C (average daily temperatures). Plants flowered 35 days faster at 29.8 °C but were 18 cm shorter than those grown at 15.2 °C. In addition, plants grown at 29.8 °C produced only one-sixth the number of flowers (with diameters that were 3.0 cm smaller) than plants grown at 15.2 °C. Days to visible bud and flowering were converted to rates, and base temperature (Tb) and thermal time to flowering (degree-days) were calculated as 4.4 °C and 606 °days, respectively. Effects of foliar applications of ancymidol (100 mg·L-1), chlormequat (1500 mg·L-1), paclobutrazol (30 mg·L-1), daminozide (5000 mg·L-1), and uniconazole (15 mg·L-1) were determined on plants vernalized for 19 weeks and then forced at 20 °C under a 16-h photoperiod. Three spray applications of uniconazole reduced plant height at first flower by 31% compared with that of nontreated controls. All other PGRs did not affect plant growth. Chemical names used: α-cyclopropyl-α-(4-methoxyphenyl)-5-pyrimidinemethanol (ancymidol); (2-chloroethyl) trimethylammonium chloride (chlormequat); butanedioic acid mono-(2,2-dimethyl hydrazide) (daminozide); (2R,3R+2S,3S)-1-(4-chlorophenyl-4,4-dimethyl-2-[1,2,4-triazol-1-yl]) (paclobutrazol); (E)-(S)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-pent-1-ene-3-ol (uniconazole).

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