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M. Helena Gomes, Randolph M. Beaudry, and Domingos P.F. Almeida

rate after cutting of cantaloupe mesocarp has been documented ( McGlasson and Pratt, 1964 ), although the steady-state respiration rates of cut melon pieces can be similar to those of whole fruit under refrigeration ( Aguayo et al., 2004 ; Watada et al

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Yoonseok Song, Hyun Ku Kim, and Kit L. Yam

Respiration rates of three blueberry (Vaccinium corymbosum L.) cultivars (Coville, Blueray, and Jersey) were measured as a function of O2, CO2, and temperature using the closed system method. The data conformed well to a recently proposed Michaelis-Menten type respiration (r) model (r = Vm [O2]/{Km + (1 + [CO2]/Ki)[O2]}), where Vm was maximum respiration rate, Km was Michaelis-Menten constant, and Ki was inhibition constant. The model predictions were used to examine the behavior of respiration rates. In general, the respiration rates decreased with increasing CO2, but were little affected by changes in O2. `Coville' blueberries had the highest respiration rate, followed by `Blueray' and `Jersey'. The temperature dependence of the respiration rates followed the Arrhenius relationship.

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Lichun Mao and Tiejin Ying

Changes in respiration rate, ethylene production, and membrane permeability of fig (Ficus carica L. `Masui Dauphine', `Celeste', and `Brunswick') fruit subjected to vibration at acceleration of 4x g for 10 min were investigated. Vibration increased respiration rate significantly, which, however, declined quickly to low level soon after the treatment. Ethylene production and membrane permeability also increased significantly during vibration. However, vibration stress up to 4x g did not have significant effect on the physiological changes of the fig fruit after vibration. `Masui Dauphine' is more susceptible to vibration stress than `Celeste' and `Brunswick'.

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P. Chowdary Talasila and Arthur C. Cameron

Modified-atmosphere (MA) packages for fruits and vegetables are traditionally designed by matching product respiration rate with permeation of the packaging film to achieve a desired gas composition in the package. However, this design procedure is adequate only in ideal situations. We have previously shown that actual O2 partial pressures were distributed around targeted levels due to variation in product respiration rate and film permeability. In some cases, injurious levels of O2 were generated as a result of this variation. We have developed a procedure that incorporates variation of product respiration rate and uses a statistical approach to predict appropriate target levels. This approach includes a user-based decision as to how many packages with O2 partial pressures below the lower O2 limit for product injury can be tolerated. We have incorporated this approach into a user-friendly computer software using turbo pascal in MS DOS environment. This software is menu-driven and has graphical support. Use of the software will be demonstrated with examples.

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Anthony Kilili, David H. Picha, and Yuehe Huang

`Beauregard' sweetpotatoes (Ipomoea batatas L. Lam) were stored under a continuous flow of 0%, 1%, 1.5%, 2%, 5%, 10%, or 21% O2 (balance N2) for 14 days. Respiration rate was significantly lower at 1.5%, 2%, 5%, and 10% O2 compared with 21% O2, while respiration at 0% and 1% O2 was higher than at 1.5%, 2%, 5%, and 10% O2. Respiration rate at 0% O2 remained high for several days after exposure to air while that at 1.5%, 2%, 5%, and 10% O2 increased rapidly to equal that of 21% O2. Ethanol and acetaldehyde accumulated rapidly at 0% and 1% O2 but were lower at the other O2 levels. Ethanol increased 16- and 4-fold after 14 days of storage at 0% and 1% O2, respectively, compared to 21% O2. In addition, acetaldehyde increased 11- and 8-fold at 0% and 1% O2 respectively, compared to 21% O2. Sucrose and total sugar concentration increased under low O2 concentration while reducing sugars (fructose and glucose) and pH decreased.

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Sylvia M. Blankenship and L. Eric Hinesley

Fraser fir [Abies fraseri (Pursh) Poir.] branches were held at 5C for 4 to 6 weeks in the following atmospheres: 1% or 3% in nitrogen; 0%, 1%, 5%, 10%, 20%, 40%, or 50% CO2 in air; or air only. Experiments were conducted in two. years during the fall, winter, and early spring. In general, CO2 ≥ 5% accelerated needle loss. There was considerable tree-to-tree variation in tolerance to elevated CO2. Oxygen at 1% killed branches, and 3% O2 showed no benefit compared to air. The initial dark respiration rate at 21C was about four times higher than at SC. Respiration decreased for ≈ 10 days and stabilized at 14% to 20% of the initial values. Respiration increased exponentially with increasing temperature between 5 and 27C. Short-term controlled or modified atmosphere storage would probably not be useful in improving the postharvest handling of Fraser fir.

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Kathleen B. Evensen and Karen M. Olson

Postproduction quality, net C exchange, and petal abscission in response to ethylene were compared following forcing at 21(day)/16C(night) or 18/13C(18-hour photoperiod) of two cultivars of Pelargonium × domesticum L.H. Bailey. Fewer petals of 2- to 6-day-old florets abscised in response to 60 minutes of 0.7 μl ethylene/liter on plants forced at low temperature than on plants forced at 3C higher temperature. Forcing temperature did not affect floret longevity or the number of florets opening during forcing, but the floral display under simulated consumer conditions was prolonged in low-temperature plants by the continued development of buds. Dark respiration rates at 21C were lower in leaves from plants forced at low temperature than in leaves of plants forced at the higher temperature. Differences in postproduction quality between plants forced at high and low temperatures may have been related to the reduced rate of carbohydrate depletion in low-temperature plants.

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Georgios Psarras and Ian A. Merwin

One-year-old potted `Mutsu' apple (Malus domestica) trees on MM.111 and M.9 rootstocks were grown outdoors from May to Nov. 1997, under three levels of soil-water availability (–20, –80, and –200 kPa), to evaluate the effects of water stress on soil/root respiration and root morphology. At weekly intervals, we measured soil/root respiration using a portable infrared gas analyzer and rootsystem size or functional activity using an electric capacitance meter. These observations were tested as nondestructive methods to estimate relative differences in root size and morphology in situ compared with final dry weight and form of excavated apple rootstocks. Root size-class distributions were estimated by digital imaging and analysis of harvested root systems. Root growth was substantially reduced by water stress; the magnitude of reduction was similar for both rootstocks, but the percentage of shoot growth reduction was higher for MM.111. Root: shoot ratios were higher and average specific respiration rates over the growing season were lower for M.9 root systems. Water stress increased the root: shoot ratio, specific root length, and carbon costs of root maintenance as indicated by specific respiration rates. Soil/root respiration was more closely correlated than root electric capacitance with actual root system size. The observed r 2 values between root capacitance and root dry weight were as high as 0.73, but root capacitance was also confounded by other factors, limiting its usefulness for nondestructive estimation of root size or activity. Rootstock genotype significantly affected root capacitance, which provided better estimates of root dry weight for M.9 than for MM.111.

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Georgios Psarras and Ian A. Merwin

One-year-old potted `Mutsu' apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] trees on scion invigorating Malling-Merton 111 (MM.111) and scion dwarfing Malling 9 (M.9) rootstocks were grown outdoors in containers under three levels of water availability (irrigated at -20, -80, and -200 kPa) to investigate the effects of soil water availability on combined soil/root (rhizosphere) respiration rates, and developmental morphology of root systems. Rhizosphere respiration was measured with a portable infrared gas analyzer, and root biomass was estimated by electrical capacitance. These nondestructive measurements were compared with final root dry weights of harvested trees, to determine their reliability for estimating relative differences in root biomass. Water stress reduced final biomass similarly for both rootstocks, but the relative reduction in shoot growth was greater for MM.111. Root to shoot ratios were higher and average specific root respiration was lower for M.9 rootstock compared with MM.111. M.9 appeared to be more tolerant of water stress then MM.111, due to reduced canopy transpiration relative to root system mass. Water stress increased root to shoot ratios, specific root length, and the carbohydrate costs of root maintenance as indicated by specific respiration rates. Root dry weight (DW) was better correlated to rhizosphere respiration than to root electric capacitance. The observed r 2 values between root capacitance and root DW were as high as 0.73, but capacitance measurements were also influenced by soil water content and rootstock type. Electrical capacitance estimated total root biomass more accurately for M.9 than for MM.111.

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Sven Verlinden, Silvanda M. Silva, Robert C. Herner, and Randolph M. Beaudry

being the most basal section cut at the time of harvesting. Respiration rates were determined after 16 h when the silicone sealant had cured and after an additional 1, 2, 3, 4, 8, 10, 16, and 23 d. Data are the average of three single-spear replications