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  • Author or Editor: Zhi Yi Tan 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.

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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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Yields and quality of witloof chicory are often low when roots are forced following several months storage or when forced at high temperatures. A technique was developed to improve the yield and quality of the chicons forced hydroponically and a method developed to determine the rates of respiration and ethylene production during the application of the technique. The technique involves the use of a resilient material (polyurethane) combined with the application of pressure to the developing chicons. Marketable yields and density of `Faro' and `Bea' chicons increased with increasing pressure applied. Increasing pressure also resulted in a significant decrease in the length to diameter ratio of chicons, an indicator of improved quality. Mechanical pressure resulted in a 3 to 4 fold greater increase in ethylene production than the control. Respiration rate increased to about twice that of the control after 10 days forcing and thereafter declined slightly. The technique provides a tool for improving economic yields of hydroponically forced witloof chicory. A possible physiological explanation for the technique is provided.

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Water manometers were connected to fruits of tomato (Lycopersicon esculentum Mill.) and pepper (Capsicum annuum L.), and then fruits were submerged in water baths providing initial temperature gradients between fruit and water of 0 to 19C. Apple (Malus domestics Borkh.) fruits, carrot (Daucus carota L.) roots, witloof chicory (Cichorium intybus L.) roots, rhubarb Rheum rhabarbarum L.) petioles, and pokeweed (Phytolacca americana L.) stems were subjected to water bath temperature gradients of 5C. Internal partial vacuums developed in all organs within minutes of imposing the gradients. The maximum partial vacuums in tomato and pepper fruits increased with increasing temperature gradients. Uptake of water accompanied changes in internal pressure reaching maxima of 17% (w/w) and 2% (w/w) of pepper and tomato fruits, respectively, after 22 hours. Maximum pressure changes achieved in bulky organs deviated from those predicted by the ideal gas law, possibly due to concomitant changes in gas pressure upon replacement of intercellular spaces with water and dissolution of CO2. Partial vacuums also developed in pepper fruits, rhubarb petioles, and pokeweed stems following exposure to air 15C cooler than initial organ temperatures. Results point to the role of temperature gradients in the transport of liquids and gases in plant organs.

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