Exogenous application of ethanol (EtOH) vapor to whole tomato fruit or excised pericarp discs inhibits ripening without affecting subsequent quality. Inhibitory EtOH levels are induced in whole tomatoes by a 72 h exposure to anaerobic atmospheres at 20C. In contrast to tomatoes, exposure to EtOH vapor (0 to 6 ml EtOH/kg FW, for 3 to 6 h at 20C) did not retard ripening (e.g., changes in external color, flesh firmness, and soluble solids) of avocado, banana, cucumber, melon, peach, or plum fruit. When the blocked replicates for nectarines were sorted by the firmness of the control fruit, higher levels of EtOH vapor appeared to delay softening of the firmer fruit. From 0 to 4 ml EtOH/kg FW was injected as 95% EtOH into the seed cavity of melon fruit through a surface sterilized area near the equator of the fruit with a plastic syringe fitted with a 7.5 cm long hypodermic needle. Injection of 1 to 4 ml EtOH/kg FW inhibited the softening of `Honey Dew' and muskmelons. Slight tissue necrosis near the site of injection was noted in a few fruit. Unlike the ripening inhibition of tomatoes which is relatively insensitive to the stage of maturity, the inhibition of melon ripening by EtOH appeared to be significantly affected by the maturity of the fruit.
Normal refrigeration (NR), low pressure (LP, 10 to 35 mm Hg), and low oxygen (0.5% to 8%) storage trials were conducted using cut flowers of carnation (Dianthus caryophyllus L.) and rose (Rosa sp.). Variables studied were storage time, gas partial pressures, vapor barriers, chemical pretreatments, grower source, cultivars, and stem recutting methods. Low oxygen storage was not beneficial regardless of variables tested. In general, carnations could be stored for 6 weeks under NR and 8 weeks under LP conditions if the flowers were pretreated with silver thiosulfate (STS) and vapor barriers were utilized during NR storage. Roses could be stored up to 2 weeks under NR and up to 4 weeks under LP conditions and still exhibit at least 61% of their nonstored, original vase-life if LP-induced leaf disorders were not considered. Rose vase-life after NR storage was enhanced by utilizing vapor barriers during storage, and visual appearance improved if stems were recut under water upon removal from storage. LP-stored roses did not benefit by these treatments. However, the same cultivars from different growers did not respond equally and great variability was noted among rose cultivars tested regardless of storage method. Of special concern were the LP-induced leaf disorders noted on ‘Forever Yours’, ‘Royalty’, ‘Town Crier’, and ‘Spanish Sun’ roses.
Maximum CO2 assimilation rates (ACO2) in citrus are not realized in environments with high irradiance, high temperatures, and high leaf-to-air vapor pressure differences (D). We hypothesized that moderate shading would reduce leaf temperature and D, thereby increasing stomatal conductance (g s) and ACO2. A 61% reduction in irradiance under aluminum net shade screens reduced midday leaf temperatures by 8 °C and D by 62%. This effect was prominent on clear days when average midday air temperature and vapor pressure deficits exceeded 30 °C and 3 kPa. ACO2 and gs increased 42% and 104%, respectively, in response to shading. Although shaded leaves had higher gs, their transpiration rates were only 7% higher and not significantly different from sunlit leaves. Leaf water use efficiency (WUE) was significantly improved in shaded leaves (39%) compared to sunlit leaves due to the increase in ACO2. Early in the morning and late afternoon when irradiance and air temperatures were low, shading had no beneficial effect on ACO2 or other gas exchange characteristics. On cloudy days or when the maximum daytime temperature and atmospheric vapor pressure deficits were less than 30 °C and 2 kPa, respectively, shading had little effect on leaf gas exchange properties. The results are consistent with the hypothesis that the beneficial effect of radiation load reduction on ACO2 is related to improved stomatal conductance in response to lowered D.
Reduced atmospheric pressures may be used to minimize mass and engineering requirements for plant growth habitats used in some extraterrestrial applications. A chamber with high vacuum capability and thermal control at Kennedy Space Center was used to measure water loss of lettuce plants at reduced atmospheric pressures. A test stand with three, high-pressure sodium vapor lamps was used to determine short-term plant responses to reduced pressure. Initial experiments with lettuce showed that a pressure of 10 kPa (≈0.1 atm) resulted in a 6.1-fold increase in the rate of water loss compared to water loss at ambient pressure. However, due to low relative humidity, plants wilted after 30 minutes exposure to 10 kPa. A follow-up experiment in which relative humidity was controlled between 70% and 85%, demonstrated that water loss was directly proportional to the vapor pressure gradient, regardless of atmospheric pressure in the pressure range of 10 to 101 kPa. However, the response was curvilinear, suggesting effects on the pathway resistance. Results indicate that plant growth at atmospheric pressures of 5 to 10 kPa should be achievable. Further work will necessitate better relative humidity control and carbon dioxide control in order to separate vapor pressure deficit effects from diffusion effects.
temperature (21 ± 1 °C) in a plastic chamber that was sealed to minimize the loss of etridiazole to the vapor phase ( Ioannou and Grogan, 1984 ). Radial growth on two axes was measured 3 d post inoculation. There was one plate per etridiazole concentration for
A method was developed to measure transpiration rates and apparent water-vapor permeability coefficients (P'H2O) of detached fruit using an analytical balance equipped with a humidity chamber, wide-range humidity-generating and sensing devices, and a datalogger. The system was designed to monitor weight changes with time and, hence, weight loss of individual fruit during exposure to specific relative humidities (RHs) and temperatures. Weight loss was corrected for loss due to respiratory exchange of 02 and CO2 before calculating P'H2O. Values of P'H2O for tomatoes obtained using this method over periods of 5 minutes to 24 hours ranged from 3 to 12 nmol·cm-2·s-1·kPa-1 at 20C, depending on the experimental conditions. These values are similar to previously published values and to those obtained in a conventional weight-loss experiment, which involved intermittent weighing. P'H20 for tomatoes dropped ≈15% in 24 hours. P'H20 increased with a transient increase in RH; the extent of the increase was variable from fruit to fruit, ranging from 5% to 100% over 30% to 90% RH. The change was reversible in that P'H2O increased and decreased within minutes following shifts in RH. Similar changes were found for strawberry P'H20. The increase in P'H2O may be due, in part, to a direct effect of water vapor on the water transport properties of the cuticular polymer and surface temperature depression as a result of evaporative cooling. At 50% RH and 20C, water vapor diffuses from tomatoes 50 times faster than O2 enters on a molar basis. This information will be useful for modeling RH changes in modified-atmosphere packages.
A monitoring and control system for sequentially measuring whole-tree-canopy gas exchange of four apple (Malus domestica Borkh.) trees in the field is described. A portable, highly transparent, open-top whole-canopy cuvette was developed for complete enclosure of the above-ground portion of the tree. The flux of whole-canopy CO2 and H2 0 vapor was estimated from differential CO2 concentration and H2O-vapor partial pressure between ambient/reference air entering the cuvette and analysis air leaving the cuvette, as measured by infrared gas analysis. The bulk air-flow rate through the chamber was measured with a Pitot static tube inserted into the air-supply duct and connected to a differential pressure transducer. Performance of the whole-canopy cuvette system was tested for its suitability for gas-exchange measurements under field conditions. The air flow through the whole-canopy cuvette was 22000 L·min-1 (≈5.5 air exchanges/min) during the day, providing adequate air mixing within the cuvette, and 4000 L·min-1 (≈1 air exchange/min) during the night. Daily average leaf temperatures within the cuvette were 2-3 °C higher than to those on trees outside the cuvette. Photosynthetic photon flux transmitted through the chamber walls was at least 92 % of the incident ambient radiation. Moreover, the whole-canopy cuvette was evaluated without tree enclosure to determine the degree of “noise” in differential CO2 concentration and H2O-vapor partial pressure and was found to be acceptable with ΔCO2 ± 0.3 (μmol·mol-1 and ΔH2O ± 5 Pa. Whole-canopy carbon gas exchange and transpiration of four cropping `Braeburn'/M.26 apple trees followed closely incident radiation over the course of a day.
The chloroform test is a good measure of fermentation, a vital step in the manufacture of black tea. Time of harvest, temperature and duration of exposure to chloroform were variables on two-leaf-and-a-bud samples to assist in selection of Chinese tea clones grown under Florida conditions. Change in color from green to deep golden brown to brown, indicative of good fermentation, took place faster and more uniformly among samples plucked in the morning. Best color development occurred at 27° to 30° C and with 150 to 180 minutes exposure to chloroform vapor.
Evapotranspiration and transpiration were determined for Aphalandra squarrosa Nees. ‘Dania’, Maranta leuconeura Kerchoviana E. Morr., Philodendron scandens subsp. oxycardium (Schott) Bunt., and Brassaia actinophylla Endl. Aphelandra transpiration was 1.5 to 2 times more per unit leaf area than other species. The hypostomatous leaves of Aphelandra and Brassaia had 151 and 131 stomata per mm2; stomatal density per mm2 was 66 for Maranta and 29 for Philodendron on abaxial surface, and 12 and 9, respectively, on adaxial surface. Midday abaxial water vapor conductance was 0.46, 0.26, 0.16, and 0.06 cm sec−1 for Aphelandra, Brassaia, Maranta, and Philodendron, respectively.
Volatile extracts were isolated from pods of southernpea by vapor-phase ether extraction. In bioassays conducted with freshly emerged adult curculios Chalcodermus aeneus (Boh.), the insects were significantly more attracted to extracts of the susceptible ‘California Blackeye No. 5’ than to air with no extracts. Extracts of the breeding lines Ala. 963.8 and CR 22-2-21 were repellent to the insects as evidenced by directed travel away from the extracts towards air alone. Gas chromatographic profiles of the 3 extracts showed obvious qualitative and quantitative differences.