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Mengmeng Gu, Curt R. Rom, James A. Robbins, and Hyun-Sug Choi

The genus Betula consists of approximately 50 deciduous species throughout northern hemisphere. Net CO2 assimilation ([A]) of four birch taxa (Betula alleghaniensis Britton, B. davurica Pall., B. nigra L. `Heritage', and B. papyrifera Marsh.) was measured with a portable gas exchange system, CIRAS-I. Light was increased from 0 to 2000 μmol· m-2·s-1 at increments of 25, 50, 100, 250, 500, 750, 1000, 1250, 1500, 1750, 2000 μmol·m–2·s–1 to create an [A] light-response curve. CO2 concentration was gradually increased to 1100 ppm in increments 50, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100 ppm to create an [A]-Ca (ambient CO2) curve. B. davurica had significantly higher potential A capacity than the other taxa under high CO2 conditions. Betula nigra `Heritage' had the highest carboxylation efficiency among four taxa. B. davurica and B. nigra `Heritage', had higher [A] when ambient CO2 is 0ppm. Betula davurica and B. nigra `Heritage', had higher light-saturated rate of gross [A] than B. alleghaniensis and B. papyrifera.

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Randolph M. Beaudry, Arthur C. Cameron, Ahmad Shirazi, and Diana L. Dostal-Lange

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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R.E. Moran, D.E. Deyton, C.E. Sams, J. Cummins, and C.D. Pless

Soybean oil can be used as an alternative pesticide for fruit trees. Two separate studies were conducted to determine the effects of oil concentration on leaf phytotoxicity and net CO2 assimilation (ACO2). In one study, concentrations of 0%, 2%, 4%, and 6% soybean oil in water were applied to individual shoots with a hand-held mist bottle. In the second study, 0%, 1.0%, and 1.5% were applied to whole trees with an airblast sprayer. Petroleum oil was applied as a separate treatment. Net CO2 assimilation was measured on single leaves. Oil residue was removed from the leaf with chloroform, dried, and weighed. Chlorosis and defoliation occurred with applications of 4% and 6% soybean oil. No visible phytotoxicity occurred with 2% or less oil. Net CO2 assimilation decreased as the rate of soybean oil increased from 0% to 4% oil, but there was no difference between 4% and 6%. Net CO2 assimilation decreased with increasing oil concentration from 0% to 1.5% and recovered to the rate of the control on day 7. Net CO2 assimilation was negatively related to oil residue. At an equivalent oil residue, there was no difference in ACO2 between petroleum and soybean oil. Below a residue of 0.15 mg·cm–2, foliar phytoxicity did not occur. Reductions in ACO2 were small and did not last longer than 7 days if residues were ≤0.10 mg·cm–2.

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Antonio Figueira, Anna Whipkey, and Jules Janick

Axillary shoots of cacao (Theobroma cacao L.), induced in vitro with cytokinins (BA or TDZ), elongated and produced leaves only in the presence of cotyledons and/or roots. Detached axillary shoots, which do not grow in `vitro under conventional tissue culture protocols, rooted with auxin and developed normally in vivo. Detached axillary shoots from cotyledonary nodes and single-node cuttings from mature plants were induced to elongate and produce normal leaves in the presence of 20,000 ppm CO2 and a photosynthetic photon flux density (PPFD) of 150 to 200 μmol·s-1·m-2. Subculture nodal cuttings continued to elongate and produce leaves under elevated CO2 and light levels, and some formed roots. Subculture of microcuttings under CO2 enrichment could be the basis for a rapid system of micropropagation for cacao. Chemical names used: N -(phenylmethyl) -1 H -purin-6-amine (BA); 1 H -indole-3-butyric `acid (IBA); α -naphthaleneacetic acid (NAA); thidiazuron (TDZ).

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R. St.Hill and D.P. Murr

Recent advances in technology have made the snapdragon, Antirrhinum majus L., a promising florist crop in North America and potentially on the Ontario market. CO2 is a known inhibitor of ethylene action, but its effects tend to be difficult to interpret based on the variable responses of plants to this gas. Recently, a gaseous ethylene analog has been shown to inhibit certain ethylene responses of cut flowers, such as wilting in carnations and flower abscission of cut phlox. This cyclic olefin, 1-methylcyclopropene (1-MCP), is thought to bind irreversibly to the ethylene receptor sites, thereby preventing or delaying ethylene responses. In the experiments undertaken, the potential of CO2 and 1-MCP were investigated for their ability to enhance vase life and to reduce shattering and wilting of snapdragons. Flowers were sealed in ≈0.2-m3 chambers encased in 6-mil polyethylene and exposed to elevated CO2 (5% or 10%) or 1-MCP (20-200 nL/L) for 6 to 24 h at 20 °C. The flowers were then exposed to continuous ethylene of 0-20 μL/L. Following exposure to 5 or 20 μL/L ethylene, 1-MCP reduced shattering ≈2- to 3-fold compared to CO2 treatment. 1-MCP did not prevent the wilting response but delayed it by ≈2 days. CO2-treated flowers exhibited a more rapid decline in net percent open florets from days 3 to 5 post-treatment. Despite the ability of 1-MCP to reduce shattering, in the absence of exposure to continuous ethylene, it has limited effectiveness on wilting compared to CO2.

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F. Medina, E.M. Yahia, L. Vazquez, and A.M. Calderón

The tolerance of “Keitt” mango to a modified atmosphere (MA) of < 0.5% O2 + 70-80% CO2 for 0 to 4 days and a controlled atmosphere (CA) of 2% O2 + 50% CO2 for 0 to 5 days was evaluated. MA and CA delayed the respiratory climacteric of the fruit. There was no significant fruit injury due to the low O2 or high CO2 atmosphere, Sensory evaluation tests did not indicate the presence of any off-flavors. Both CA and MA increased the activity of the enzyme ATP: Phosphofructokinase, did not effect the activity of pyruvate kinase, and MA reduced the activity of PPi: phosphofructokinase. MA reduced the levels of frutose 6-phosphate, while phosphoenolpyruvate and pyruvic acid were not effected by both atmosphere treatments Although insecticidal O2 and CO2 atmosphere resulted in changes in the glycolitic activity, there was no indication of any injury and fruits were ripened normally, This work indicates the potential of the application of M/CA for postharvest insect control in mango.

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Jonathan Frantz and Peter Ling

Bedding plant petunia (Petunia ×hybrida) is often produced with high nutrient concentrations as a cool-season crop. How a plant uses the nutrients supplied will depend in large part on the environmental factors influencing growth rate, such as light and CO2. Since more growers are considering using supplemental CO2 to improve energy efficiency for plant production, it is important to understand light and fertilizer levels needed for efficient production of high-quality plants. Using a multi-chamber controlled environment system, petunia plants were grown from seed for 6–8 weeks after transplanting into different light and CO2 environments and fed with either a low (7.1 mM N) or high (21.3 mM N) fertilizer regime. Plants were evaluated for appearance, harvested periodically, and separated into flower, stem, and leaf biomass. Biomass was then dried and analyzed with ICP-OES for essential macro- and micronutrients. Low-fertilizer-grown plants had consistently earlier and more flowers, but showed symptoms of nutrient deficiencies in the final few weeks of production at all light and CO2 levels. There were significant interactions between light and fertilizer treatments for different nutrients. Calcium uptake was greatly influenced by light level, Fe, P, and K were influenced by the fertilizer supply, and Mg and B were inversely influenced by fertilizer supply at high light. These data suggest new management strategies are needed to improve fertilizer use efficiency in different environments.

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F. Medina, E.M. Yahia, L. Vazquez, and A.M. Calderón

The tolerance of “Keitt” mango to a modified atmosphere (MA) of < 0.5% O2 + 70-80% CO2 for 0 to 4 days and a controlled atmosphere (CA) of 2% O2 + 50% CO2 for 0 to 5 days was evaluated. MA and CA delayed the respiratory climacteric of the fruit. There was no significant fruit injury due to the low O2 or high CO2 atmosphere, Sensory evaluation tests did not indicate the presence of any off-flavors. Both CA and MA increased the activity of the enzyme ATP: Phosphofructokinase, did not effect the activity of pyruvate kinase, and MA reduced the activity of PPi: phosphofructokinase. MA reduced the levels of frutose 6-phosphate, while phosphoenolpyruvate and pyruvic acid were not effected by both atmosphere treatments Although insecticidal O2 and CO2 atmosphere resulted in changes in the glycolitic activity, there was no indication of any injury and fruits were ripened normally, This work indicates the potential of the application of M/CA for postharvest insect control in mango.

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H. John Elgar, Douglas M. Burmeister, and Christopher B. Watkins

`Braeburn' apple (Malus ×domestica Borkh.) fruit can be susceptible to the development of an internal disorder called “`Braeburn' browning disorder” (BBD). Factors associated with development of this disorder were investigated. Susceptibility to injury was greater in fruit exposed to 2 or 5 kPa CO2 than to 0 kPa CO2 during storage. Susceptibility also increased with decreasing O2 partial pressure in the range of 5 to 1 kPa in the storage atmosphere. However, fruit stored in 1 kPa O2 remained firmer than those stored at higher partial pressures, regardless of CO2 level. BBD appeared to develop during the first 2 weeks of storage, and delays in air at 0 °C prior to controlled-atmosphere (CA) storage decreased incidence and severity of the disorder. The incidence of BBD was also reduced when the time to establish CA conditions was prolonged. We recommend that `Braeburn' apples be stored under CA conditions of ≤1.0 kPa CO2 and 3.0 kPa O2. Delayed application of CA for 2 weeks after fruit enter the coldstorage may also reduce development of BBD.

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Rajasekaran R. Lada, F. Christine Pettipas, Steve Kyei-Boahen, Robert Gordon, and Tess Astatkie

Genotypes and environmental parameters interactively act on plants and modify their yield responses through modifying photosynthetic processes. In order to optimize yield, it is critical to understand the photosynthetic behavior of the crop as altered by genotypes and environment. Leaf gas exchange parameters of carrot (Daucus carota L.) cultivars Cascade, Carson, Oranza, and Red Core Chantenay (RCC) were examined in response to various irradiances, fertility levels, moisture regimes, and to elevated CO2 concentrations. Leaf net photosynthetic rate (PN), stomatal conductance (gs), and transpiration rate (E) were measured. Cultivars responded similarly to increasing PAR and CO2 concentrations and did not differ in photosynthetic parameters. Increasing PAR from 100 to 1000 μmol·m-2·s-1 increased PN, which did not reach saturation. The gs and E increased to a peak between 600 and 800 &#956;mol·m-2·s-1, then rapidly declined, resulting in a sharp increase in water use efficiency (WUE). Increasing CO2 concentrations from 50 to 1050 μmol·mol-1 increased PN until saturation at 650 μmol·mol-1. The gs and E increased to a peak at 350 μmol·mol-1 and then declined. WUE increased linearly with increasing CO2. Carrots exposed to drought over a period of 5 days decreased PN and E. The PN decrease was cultivar specific. Nutrient concentrations of 0 to 400 ppm gave a similar pattern of decrease for PN, E, and gs. Treatment of 50 ppm had the highest PN, E, and gs. The WUE generally increased with increasing nutrient concentration.