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Abstract

Decay of apples (Malus sylvestris Mill.) inoculated with Penicillium expansum was controlled by acetaldehyde vapor concentrations (v/v) of 0.5% for 180 min, 1% for 120 min, 2% for 60 min, and 3% for 30 min. The above treatments did not produce lenticel or skin injury. Fumigated conidia did not germinate in 21 days at 21°C on artificial media and failed to induce decay in stem-punctured apples. The pathogen could not be re-isolated from fumigated inoculated punctures, however, the pathogen was obtained from inoculated punctures not exposed to acetaldehyde vapor. Fungicidal action of acetaldehyde vapor was a function of concentration and exposure period. Objectional off-flavors were not detected in fumigated apples, although appreciable amounts of acetaldehyde vapor were absorbed.

Open Access

Research quantified contributions to total variation in water vapor permeance from sources such as cultivar and harvest date in `Braeburn', `Pacific Rose', `Granny Smith', and `Cripps Pink' apples [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.]. In a study on `Braeburn' fruit from eight orchards in Central Otago, New Zealand, >50% of the total variation in permeance was associated with harvest date. This variation was the result of a large increase in water vapor permeance from 16.6 to 30.2 (se = 0.88, df = 192) nmol·s-1·m-2·Pa-1 over the 8 week experimental harvest period. Fruit to fruit differences accounted for 22% of total variation in permeance. Interaction between harvest date and orchard effects explained 7% of the total variation, indicating that fruit from the different orchards responded in differing ways to advancing harvest date. Tree effects accounted for only 1% of the total variation. Weight loss from respiration [at 20 °C and ≈60% relative humidity (RH)] comprised 3.04±0.11% of total weight loss, averaged across all harvest dates. In a second study of fruit of four apple cultivars, almost 30% of the total variation in water vapor permeance was associated with cultivar differences. Mean water vapor permeance for `Braeburn', `Pacific Rose', `Granny Smith', and `Cripps Pink' fruit was 44, 35, 17, and 20 (se = 4.3, df = 300) nmol·s-1·m-2·Pa-1 respectively. Over 20% of the total variation was associated with harvest date and arose from a large increase in water vapor permeance from 21 nmol·s-1·m-2·Pa-1 at first harvest to 46 nmol·s-1·m-2·Pa-1 (se = 5.3, df = 200) at final harvest, 10 weeks later, on average across all four cultivars. There was large fruit to fruit variation in water vapor permeance accounting for 25% of the total variation in permeance values. Tree effects only accounted for 4% of the total variation. Water vapor permeance in `Pacific Rose'` and `Braeburn' increased substantially with later harvest but values remained relatively constant for `Granny Smith' and `Cripps Pink'. A simple mathematical model was developed to predict weight loss from `Braeburn' fruit. Based on these findings, it appears worthwhile to increase the stringency of measures to control weight loss in `Braeburn' and `Pacific Rose'` apples, particularly those harvested late in the season.

Free access

Quantitative differences in leaf abscisic acid (ABA) among Acer rubrum L. (red maple) ecotypes were investigated. This study tested the hypothesis that seedlings from wet and dry maternal sites display distinctly different capacities to synthesize ABA in response to atmospheric vapor pressure deficits. The increased levels of ABA in leaf tissue in the red maple ecotypes were associated with atmospheric vapor pressure deficit (VPD). Leaves on well-watered plants responded to VPD by increasing their ABA levels and reducing their photosynthesis (Anet) and stomatal conductance (gs). Both ecotypes appear to accumulate ABA at about the same rate as VPD increased. Despite the similar accumulation rates between ecotypes, wet site ecotypes consistently had a higher level of ABA present in leaf tissue under both low and high VPD conditions. Furthermore, wet site provenances appear to reduce Anet and gs in response to ABA accumulation, whereas dry sites do not present as clear an ABA/gs relationship. This study shows variation between wet and dry site red maple populations in physiological response to atmospheric vapor pressure deficits, indicating that natural ecotypic variation in stomatal responsiveness to air humidity is likely mediated by ABA accumulation in leaf tissue. This research demonstrates that ecotypes of red maple may be selected for atmospheric drought tolerance based on site moisture conditions.

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Tomatoes (Lycopersicon esculentum Mill. `Bermuda') were vacuum infiltrated at the breaker stage with 25 to 55 mL·L-1 ethanol (EtOH) vapor at a 10 kPa pressure for 5 minutes and then held for a further period before ripening in air at 22 °C. Fruit could tolerate these EtOH vapor concentrations for no longer than 0 to 12 hours after vacuum infiltration, depending on concentration; otherwise skin pitting, uneven ripening and off-flavors resulted. Noninjurious conditions delayed ripening, as judged by color change, by an additional 1 to 5 days compared with 4 days for the control; aroma or flavor were not altered as determined by a trained taste panel, except in extreme conditions where in some cases off-flavors increased. Soluble solids and titratable acidity did not vary, but pH increased by 0.1 units in some treatments. In control fruit EtOH was found only in the gel tissue, and acetaldehyde (AA) was higher in the gel tissue compared with the pericarp and columella, indicating different metabolic behavior of the various tomato tissues. During vacuum exposure, EtOH moved through the stem scar and to a much lesser extent through the epidermis; during subsequent exposure to EtOH more EtOH moved through the epidermis than before, but still less than through the stem scar. AA increased following EtOH uptake, but all increases in EtOH and AA disappeared before fruit ripened.

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Midday reductions of stomatal conductance and carbon dioxide assimilation rates (Aco2) in Citrus are typically attributed to large leaf-to-air vapor-pressure differences or high atmospheric vapor-pressure deficits (VPD). This study investigated air temperature (Ta) and available soil water (ASW) level as corollary factors of atmospheric VPD that influence midday reduction of net gas exchange in citrus leaves. The influence of elevated atmospheric CO2 under conditions that inhibit net canopy Aco2 was also investigated. Net canopy Aco2 and evapotranspiration rates of Carrizo citrange [Poncirus trifoliata Raf × Citrus sinensis (L.) Osbeck] and Swingle citrumelo (P. trifoliata Raf × C. paradisii Macf.) seedlings grown in outdoor controlled-environment growth chambers were measured under two levels of Ta with concomitant changes in VPD and two levels of atmospheric CO2 concentration, which were changed in steps over time. Cyclical depletion of ASW was allowed to occur at each set of Ta/VPD and CO2 combinations. Highest net canopy Ace, rates at ambient CO2 concentration (330 μmol·mol-1) were obtained at the low Ta/VPD level (29C/2.4 kPa) and ASW >50%. Diurnal canopy CO2 uptake rates decreased at the high Ta/VPD level (37C/3.6 kPa), and midday depression of canopy Aco2 was observed at ASW levels <50%. Net canopy Aco2 decreased at higher levels of ASW under the high Ta/VPD treatment than at the low Ta/VPD treatment. At the elevated CO2 concentration (840 μmol·mol-1) net canopy CO2 uptake rates were double those that occurred at ambient CO2 levels and they did not exhibit midday reduction. Our data indicate that, when soil water is not readily available, citrus seedlings are more sensitive to high levels of Ta and VPD which results in reduction of CO2 uptake. The inhibitory effects of elevated VPD and reduced ASW on citrus net Aco2 were lessened at the elevated atmospheric CO2 level.

Free access

High temperature reduces fruit set in bell pepper [Capsicum annuum L. var. annuum (Grossum Group)], and reduction of pepper productivity, resulting from high temperature, may be a direct effect of temperature or an indirect effect of water stress induced by increased vapor pressure deficits (VPDs) at high temperature. We evaluated responses of plant growth, reproduction, net photosynthesis (PN), chlorophyll fluorescence, predawn respiration, leaf water potential, and stomatal conductance of `Ace' and `Bell Boy' bell pepper to elevated temperature (33 °C) with increased VPD (2.1 kPa) or elevated temperature with no increase in VPD (1.1 kPa). VPD had no effect on flower number or fruit set and did not adversely influence the physiological processes measured. Therefore, deleterious effects of high temperature on pepper fruit set does not appear to be temperature induced water stress, but is more likely a direct temperature response. Elevated temperature decreased fruit set but not flower production. Gas exchange measurements suggest failure to set fruit was not due to reduced leaf photosynthesis.

Free access

Abstract

CO2 assimilation (A), leaf conductance to water vapor (gl), mesophyll conductance (gm), and water use efficiency (WUE) were compared for two cultivars of highbush (Vaccinium corymbosum L.) and a wild diploid lowbush blueberry species (Vaccinium darrowii Camp.) in response to PPF, CO2, temperature, and vapor pressure deficit (VPD) to determine if apparent tolerance of V. darrowii to high temperature and drought conditions resulted from differences in gas exchange characteristics. Cultivar differences between ‘Bluecrop’ and ‘Jersey’ in A were not significant when expressed on a leaf area, leaf dry weight, or total chlorophyll basis. Maximum CO2 assimilation rates for V. darrowii were about 35%, 50%, or 40% lower than highbush cultivars when expressed on a leaf area, leaf dry weight, or total chlorophyll basis, respectively. Differences between ‘Bluecrop’ and ‘Jersey’ were also non-significant for mesophyll conductance, transpiration, CO2 compensation points, and water use efficiency. CO2 assimilation maximized between 600-800 µmol·s–1·m–2 photosynthetic photon flux (PPF) for all three genotypes and the temperature optima ranged between 18° and 26°C for ‘Jersey’, 14° and 22° for ‘Bluecrop’, and 25° and 30° for V. darrowii. As temperature was increased from 20° to 30°, leaf conductance (gl) to water vapor was lower and water use efficiency was higher for V. darrowii, compared to ‘Bluecrop’ but not ‘Jersey’. There was a 50-65% reduction in gl as VPD was increased, but only 10–20% reduction was observed in A. Leaf conductance to water vapor was reduced for V. darrowii, which restricted intercellular CO2. Since crosses are possible between highbush and V. darrowii, it is possible that heat tolerance and/or drought resistance could be improved in Highbush blueberry through the incorporation of genes from V. darrowii.

Open Access

Hexanal vapor inhibited hyphae growth of Penicillium expansum and Botrytis cinerea on potato dextrose agar (PDA) and on apple (Malus domestica Borkh.) slices. After 48 hours exposure to 4.1 μmol·L-1 (100 ppm) hexanal, the hyphae growth of both fungi was about 50% that of untreated controls. At a concentration of 10.3 μmol·L-1 (250 ppm), neither fungus grew during the treatment period, however, some growth of both fungi occurred 120 hours after treatment. At concentrations of hexanal vapor of 18.6 μmol·L-1 (450 ppm) or more, the growth of both fungi ceased and the organisms were apparently killed, neither showing regrowth when moved to air. When fungi were allowed to germinate and grow for 48 hours in hexanal-free air, a subsequent 48-hour exposure to 10.3 μmol·L-1 hexanal slowed colony growth relative to controls for several days and a 48-hour exposure to 18.6 μmol·L-1 stopped growth completely. Concentrations of hexanal that inhibited fungal growth on PDA also retarded decay lesion development on `Golden Delicious' and on `Jonagold' apple slices. Hexanal was actively converted to aroma volatiles in `Jonagold' and `Golden Delicious' apple slices, with hexanol and hexylacetate production strongly enhanced after 20 to 30 hours treatment. A small amount of butylhexanoate and hexylhexanoate production was also noted. Within 16 hours after treatment, no hexanal could be detected emanating from treated fruit. Since hexanal was metabolized to aroma-related volatiles by the fruit slices, the possibility of hexanal being an essentially residue-less antifungal agent seems likely. The possibility of developing a system for treating apple slices with hexanal in modified-atmosphere packages was also examined. The permeability of low-density polyethylene (LDPE) film to hexanal and hexylacetate was, respectively, about 500- and 1000-fold higher than LDPE permeability to O2. The permeability of both compounds increased exponentially with temperature, with hexanal permeability increased 6-fold while hexylacetate increased only 2.5-fold between 0 and 30 °C.

Free access

`Gala' apples [Malus silvestris (L.) var. domestica (Borkh.) Mansf.] were treated with ethanol vapor (5 mL·kg-1 fruit for 24 hours at 25 °C), heat (4 days at 38 °C and >98% RH), or 1-methylcyclopropene (1-MCP; 1 or 0.625 μL·L-1 for 18 hours at 20 °C) before processing into slices, then dipped in anti-browning solutions or coatings, drained, and packaged in perforated polyethylene bags. Residual effects of pretreatments on fresh-cut slice physiological and quality attributes were investigated during storage for up to 19 days at 5.5 °C. Ethylene production was reduced by ethanol, heat, and 1-MCP pretreatments, while ethanol and heat also reduced slice respiration. Heat and 1-MCP pretreatments inhibited slice texture changes, while ethanol had no effect on instrumental texture measurements but reduced sensory firmness. Ethanol pretreatment increased the contents of ethanol and ethyl esters in slices but reduced acidity, while heat reduced both acidity and aroma volatile levels. Both ethanol and heat pretreatments led to lower sensory scores for apple flavor and ethanol-pretreated slices also received higher scores for altered flavor, although all scores were in the acceptable range. Slice acidity was best maintained by 1-MCP pretreatment. Shelf life based on appearance was 15 to 16 days for ethanol-pretreated slices and 12 days for heat-pretreated slices compared to that of control, which was 8 to 9 days, while 1-MCP pretreatment promoted decay development on the cut surface, which reduced the shelf life to 7 to 8 days. Obvious separations were determined between ethanol- and heat-pretreated slices and untreated control by canonical discriminant analysis of headspace volatile levels determined by GC and electronic nose. Therefore, pretreatments with ethanol and heat are very effective for prolonging visual shelf life at the expense of aroma quality.

Free access

Abstract

Clonal plants of four olive (Olea europaea L.) cultivars that originated in cool, moderately hot, and hot climates were examined for their photosynthetic potentials. Within 3 to 4 weeks, plants had fully expanded leaves; by 3 months the apparent photosynthesis, A, increased to a maximum of 5.4 µmol CO2/m2 per sec, while the water use efficiency (WUE) was 2.6 mmol CO2/mol H2O. The mean chloropohyll content was 0.564 mmol/chlorophyll (a + b)/m2. Mean assimilation rate was negatively correlated to leaf area. The values of A were three to four times less than those reported for apple and almond, whereas WUE was 22% greater. A values were proportional to stomatal conductance. Mesophyll resistance was higher than several C3 plants and the optimum temperature for photosynthesis varied among cultivars, seemingly according to the climate where they originated. Stomata opened and closed within 10 min in response to changes in humidity. Gas exchange properties were not affected by peltate removal.

Open Access