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  • Author or Editor: Kenneth A. Corey x
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A method was developed to improve the yield and quality of chicons of witloof chicory (Cichorium intybus L.) forced hydroponically from roots taken following long-term storage. The method combines the use of a resilient material (polyurethane foam) with the application of pressure to the developing chicons. At the start of forcing, weights of 0, 150, 300, 450, and 900 g/root were applied to the crown and maintained until harvest. Marketable yields and density of chicons of the late-forcing cultivar Faro increased with increasing weight applied. Increasing weight also significantly decreased the length: diameter ratio of chicons, an indicator of quality. Increased marketable yield and improved quality of `Bea' (intermediate to late-forcing cultivar) chicons were achieved with application of 450 g/root. The technique provides a tool for improving economic yields of late-season, hydroponically forced witloof chicory.

Free access

Urea fertilization of `Heinz 1350' tomato (Lycopersicon esculentum Mill.) in sand or soil culture did not enhance ethylene evolution or restrict growth relative to plants receiving \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathbf{NO}_{\mathbf{3}}^{\mathbf{-}}\) \end{document} whereas \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathbf{NO}_{\mathbf{4}}^{\mathbf{+}}\) \end{document} nutrition doubled the relative rates of ethylene evolution and restricted relative growth. Inhibitors of N transformations in media (nitrapyrin, Np; hydroquinone, HQ; and phenylphosphorodiamidate, PPD) had no apparent stimulator effects on ethylene evolution of plants grown on urea or \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathbf{NO}_{\mathbf{3}}^{\mathbf{-}}\) \end{document} nutrition in sand or soil. Ethylene evolution was enhanced by PPD relative to that by Np or HQ for plants receiving \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathbf{NO}_{\mathbf{4}}^{\mathbf{+}}\) \end{document} nutrition. Each inhibitor had toxic effects on plant growth. Increasing K+ supply from 0 to 8 mm in nutrient solutions decreased ethylene evolution and increased plant growth with urea fertilization. Urea had low phytotoxicity if its hydrolysis to \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathbf{NO}_{\mathbf{4}}^{\mathbf{+}}\) \end{document} was prevented in the media. Chemical names used: p-dihydroxybenzene (hydroquinone); benzenephosphorodiamide (phenylphosphorodiamidate); 2-chloro-6-(trichloromethyl)pyridine (nitrapyrin).

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Inhibitors of ethylene synthesis and action were used to alleviate ammonium toxicity in tomato (Lycopersicon esculentum Mill. `Heinz 1350') grown on ammonium-based nutrient solutions. Aminooxyacetic acid and Ag+ were effective in reducing ammonium toxicity, whereas Co+2 and salicylic acid were not. A hypothesis was developed to integrate ammonium accumulation and ethylene biosynthesis into a mechanism for expression of plant injury from environmental stresses.

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Procedures for predicting optimum packaging conditions of modified atmosphere packages (MAP) of tomato (`Heinz 1370') were developed. The relationship between O2 consumption rate and O2 concn (RRo2) was determined using O2 depletion data collected by enclosing tomatoes in jars and sampling head space O2 concn over time. The fitted function was then used in conjunction with other input variables: (1) film permeability to O2 (PO2), (2) film surface area (A), and (3) fruit weight in packages (Wp) to develop the final predictive equation based on Fick's law of gas diffusion. Predictive power of the equation was tested by comparing the steady state O2 concn achieved experimentally with those predicted for a wide range of packaging conditions. Packaging conditions included film surface area, weight of fruit in packages, and O2 permeability of the film (0.0426 and 0.0620 ml/kg hr). Prediction curves showing steady state O2 concn vs. packaging ratio (A/Wp) closely resembled the best fit curves of data. The effect of temperature on steady state O2 concn in MA bags was also examined. Increasing temperature from 20°C to 28±2°C had little effect but decreasing temperature to 10°C led to higher in-package O2 concn. Results indicate that predictive equations can be used to select appropriate films and optimize packaging ratios to achieve desired steady state O2 concn for MAP of tomatoes.

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A rapid steady state method for measurement of gas permeability of polymeric films was developed. Films were sealed between two equal volume chambers with pure O2 and pure N2 flowing through opposite sides. Oxygen concentration in the N2 cell was measured over time until steady state was reached. The method was used to determine oxygen permeability of two different films. Results from four replications on each film indicated excellent repeatability with coefficients of variation less than 3%. The time required to reach steady state oxygen concentration was dependent upon film type, flow rate, and temperature. The higher the N2 flow rate the shorter the time to reach steady state O2 concentrations. The slowest measurement at the lowest flow rate of 27 ml/min took less than 3 hours to collect the data necessary to achieve steady state. Increasing temperature from 10°C to 20°C resulted in an approximately 40% increase in O2 permeability for both films tested. The technique will be a valuable tool for measuring permeabilities of new films and the same film at different temperatures, and for selecting the appropriate material for modified atmosphere packaging of fresh produce.

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Diurnal changes in air and soil temperatures lead to temperature gradients between air and soil, between roots and shoots, and within plant organs. In response to these gradients, fluctuations in gas pressures may develop in organs that are resistant to exchange of gases. These fluctuations may regulate mass flow of gases or solutions within plants. Patterns of diurnal temperature changes were generated to illustrate temperature gradients between roots and shoots. Experimental confirmation of pressure changes induced by temperature differences between roots and shoots were measured with water manometers attached to stumps of detopped tomato plants. When roots were maintained 8 C lower than shoots, internal pressure decreased by 22 cm H2O. Reversing the direction of the temperature gradient led to an approximately equal and opposite pressure change and to sap movement. These results support a hypothesis that internal pressure gradients resulting from temperature gradients contribute to transport of substances in plants.

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It frequently takes days to weeks for testing films to determine if desired steady state concn of gases are reached when atmospheres are passively modified through commodity respiration. Our objective was to develop a rapid method to test the appropriateness of packaging films and designs using active modification of the atmosphere. Repeated exposures of commodities to partial vacuum were followed by infusion of N2 to 1 atm. Three to five minutes were allowed following each N2 infusion. Initial O2 concn achieved in packages (polyethyl vinyl acetate) depended upon the extent of the vacuum and the number of exposures. Within packages of tomatoes, O2 concn of 8.3 ± 0.5% and 5.0 ± 1.0% were measured following exposure to 460 and 360 mm Hg vacuum, respectively. Three exposures of cabbage and muskmelon packages to 460 mm Hg resulted in O2 concn of 5.1 ± 1.4% and 5.0 ± 1.4%, respectively. Maintenance or deviation from actively established atmospheres was determined within hours.

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Abstract

Ethylene evolution was determined for tomato (Lycopersicon esculentum Mill.) plants grown under nutrient-deficient (N, P, K, Ca, Mg, S) conditions or under full nutrition with NH4 + or NO 3 in sand culture. Ethylene evolution increased for plants deficient in K, Ca, or Mg relative to that of plants grown on nutritionally complete solutions with NO 3 . Deficiency of N, P, or S did not stimulate ethylene evolution relative to that detected from plants grown with complete nutrition with NO 3 . Physiological stress from NH4 + nutrition produced enhancements in ethylene evolution that exceeded those due to deficiencies of macronutrients.

Open Access

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.

Free access

Abstract

Ripening of ‘Charleston Gray’ watermelon fruits was accompanied by changes in the appearance and quantity of surface waxes. The structure of surface wax platelets observed with a scanning electron microscope changed from an intricate porous appearance for unripe fruits to a smoother, less porous appearance for optimally ripe and overripe fruits. Structural changes in waxes as fruit matured from the unripe to overripe stages were accompanied by a 71% increase in the quantity of epicuticular waxes. These observations suggest the possibility of monitoring the ripeness of watermelon fruit through changes that occur in the appearance and structure of surface waxes.

Open Access