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Joshua D. Butcher, Charles P. Laubscher and Johannes C. Coetzee

and the production of essential oils in P. tomentosum. Literature Cited Ben-Yaakov, S. Ben-Asher, Y. 1982 Continuous measurements of dissolved oxygen in water culture by a self-calibrating monitor Water Res. 16 169 172 Bonachela, S. Vargas, J.A. Acuña

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Daniel P. Gillespie, Chieri Kubota and Sally A. Miller

Rootzone pH affects nutrient availability for plants. Hydroponic leafy greens are grown in nutrient solutions with pH 5.5 to 6.5. Lower pH may inhibit plant growth, whereas pathogenic oomycete growth and reproduction may be mitigated. General understanding of pH effects on nutrient availability suggests likely toxicity and deficiency of specific micronutrients. We hypothesized that if adjustments are made to the micronutrient concentrations in solution, plants will grow in lower-than-conventional pH without nutrient disorders, while oomycete disease incidence and severity may be reduced. To develop a new nutrient solution management strategy, we examined pH of 4.0, 4.5, 5.0, and 5.5 with or without micronutrient adjustments for growing two cultivars of basil plants Dolce Fresca and Nufar in a greenhouse hydroponic deep-water culture (DWC) system. Micronutrient adjustments included reduced concentrations of copper, zinc, manganese, and boron by one-half and doubled molybdenum concentration. Plants harvested 20 to 28 days after transplanting did not show significant effects of pH or the micronutrient adjustment. Phosphorus, calcium, magnesium, sulfur, boron, manganese, and zinc concentrations in leaves significantly declined, while potassium and aluminum concentrations increased with decreasing pH. However, these changes and therefore micronutrient adjustments did not affect basil plant growth significantly. ‘Nufar’ basil plants were then grown in a growth chamber DWC system at pH 4.0 or a conventional 5.5 with and without inoculation of Pythium aphanidermatum zoospores. Fourteen days after inoculation, P. aphanidermatum oospore production was confirmed only for the inoculated plants in pH 5.5 solution, where a significant reduction of plant growth was observed. The results of the present study indicate that maintaining nutrient solution pH at 4.0 can effectively suppress the severity of root rot caused by P. aphanidermatum initiated by zoospore inoculation without influencing basil growth.

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T. Tamada

The fertilizer responsiveness to macronutrients of `Woodard' was investigated to obtain the data for the recommended rate of fertilizer application in a rabbiteye blueberry.

One-year-old rooted cuttings of 'Woodard was grown under water culture in 1991. The plot was consisted of 13, a control (application rate: N-28, P-30, K-40, Ca-40, Mg-24 ppm) and 12 high volume application plots of macronutrients (applicated 5 times that of the control).

The growth (dry mater per bush) was most superior in the N+Mg plot, most inferior in the N+Ca, the other plots was medium. As compared with the control, the growth of N+Mg, P+K, P+Ca, P+Mg, K+Ca, K+Ca+Mg and Ca+Mg plots was better than the control, and the growth of N+K, N+P+K and K+Mg plots was below. The concentration of macroelements in leaves of the control plot was low among all of. In each plots of high volume application of macronutrients, the concentration of the macroelements in leaves with some exceptions, became high, and the interaction between nutrient elements was confirmed. The difference of the growth of `Woodard' was considerd to be caused not only by the excess of some macroelements but also the imbalance of certain elements in the leaf and root.

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M.A. Sherif, P.A. Loretan, A.A. Trotman, J.Y. Lu and L.C. Garner

Nutrient technique (NFT) and deep water culture (DWC) hydroponic systems were used to grow sweetpotao to study the effect of four nutrient solution treatments on: translocation of nutrients and plant and microbial population growth in split-root channels. 'TU-155'cuttings (15 cm) were prerooted for 30 days in sand in 4 cm CPVC pipes 46 cm in length. A modified half Hoagland (MHH) solution was supplied ad libidum. After 30 days, plants were removed and the roots of each plant were cleaned and split evenly between two channels (15 cm deep by 15 cm wide by 1.2 m long). four plants per channel. Nutrient solution treatments (replicated) were: MHH-MHH: MHH-Air, MHH-deionized water (DIW); and monovalent (Mono) - divalent (Dival) anions and cations. Solution samples were continuously collected at 7-day intervals for microbial population profiling. Plants were harvested after growing for 120 days in a greenhouse. Storage roots, when produced, were similar in nutritive components. However, no storage roots were produced in Air or Mono channels and only a few in DIW. Fresh and dry weights for storage roots and foliage were highest in MHH-MHH in both NFT and DWC in repeated experiments. Population counts indicated that nutrient solution composition influenced the size of the microbial population in NFT. Population counts were highest in Dival channels. The microbial population counts (4.20-7.49 cfu/mL) were. relatively high in both NFT and DWC systems.

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Dariusz Swietlik

Sour orange seedlings were grown in water culture to which one of seven aromatic compounds, associated with allelopathic effects, was added to produce concentrations ranging from 0.5 to 2.0 mM. Leaf water potential (ψ1), leaf stomatal conductance (gs), and whole plant transpiration (T) were measured during a 7-day treatment period. At the end of that period, the total and average leaf surface area, shoot elongation, and fresh weight gain of seedlings were determined. Solutions of vanillic, coumaric, and ferulic acids of 2mM concentration reduced ψ1, gs, and T. Reductions of gs, and T but not (ψ1) occurred when vanillic acid of 1mM concentration was applied. Solutions of vanillic (0.5; 1.0; 2.0mM), coumaric (1; 2mM), cinnamic (1mM), or chlorogenic (1; 2mM) acids reduced fresh weight gain of seedlings. Only the coumaric and chlorogenic acids treatments of 2mM concentration reduced shoot elongation. No treatment affected total or individual leaf area. Gallic and caffeic acids had no effect on sour orange water relations and growth.

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John E. Fucik and Dariusz Swietlik

Water extracts of cocklebur,CBX (Xanthium spinosa L.) and velvetleaf,VLX (Abutilon theophrasti Medic.) shoots and Mexican ash,AshX (Fraxinus Berlandieriana A.DC.) roots were added to 9 month-old sour orange Citrus aurantium L.) seedlings(SOs) in water culture. Final extract concentrations represented either 50 or 12.5 g. of plant material liter-1 of culture solution, i.e. 1/20 or 1/80 dilutions. Leaf water potential(ψ); stomatal conductance(gs);transpiration(T) and growth responses were measured for 13 days. After 1 day, SOs in AshX and CBX had lower ψ than controls. After 11 days SOs in CBX had higher ψ than the others. ψ responded similarly to both extract concs.. Thru day 5, AshX decreased gs vs. the controls and VLX. By day 11, gs of SOs in AshX was less than for VLX but not the others. On days 1 and 5, gs for VLX at 1/20 was lower than controls but at 1/80, gs's were the highest of all treatments. These results supported by the T rates, growth responses and others findings suggest AshX and VLX induce water stress by reducing water absorption and/or transport in addition to possibly disrupting normal root/shoot communications

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Sissel Torre, Tove Fjeld, Hans Ragnar Gislerød and Roar Moe

Single node cuttings with one mature leaf were taken from Rosa ×hybrida `Baroness' and rooted in water culture. The plants were subjected to either 90% (high) or 70% (moderate) relative humidity (RH) in climate chambers. Single stem roses with intact roots were transferred to 40% (low) RH to investigate the stomatal response to water stress. Moderate RH plants showed decreasing leaf conductance from day 1 to day 3 during both light and dark phases, in contrast to high RH roses, which showed almost similar leaf conductances during the 3 days. Leaf samples were studied with a light microscope (LM) and a scanning electron microscope (SEM) to quantify morphological and structural changes. Epidermal imprints showed a significantly higher number of stomata and longer stomata, as well as a wider stomatal apertures on roses grown at high RH. The high RH leaves showed a reduced density of vascular tissue and thinner leaves when compared to moderate RH leaves. Enlarged intercellular air-space (ICA) was found due to a reduced number of spongy and palisade mesophyll cells. No obvious difference in shape, size, undulation or the structure of the epicuticular wax was observed in SEM between high and moderate RH grown leaves. In conclusion, roses subjected to high RH showed differences in leaf anatomy, stomatal morphology and stomatal function, which may explain the loss of water control of these plants. Stomatal ontogenesis should occur at RH conditions below 85% to secure roses with a high postharvest quality potential.

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Weixing Cao and Theodore W. Tibbitts

A system maintaining continuous water tension on a nutrient solution has been developed to control root zone moisture levels for plants in microgravity conditions. This study was conducted in a growth chamber to characterize potato (Solanum tuberosum L.) responses to constant water tension compared to plants grown with no tension using a free-water technique. In three separate experiments, plants were grown in trays filled with a 4-cm layer of 1-mm-diameter isolite (porous ceramic) particles. Ten porous stainless-steel tubes, 4 cm apart, were buried in the medium, and nutrient solution was drawn through the porous tubes under a constant water tension of -0.5 kPa maintained with a siphon system. For the free-water treatment, trays were slanted, and solution was supplied along the upper end of trays, passed under the medium, and then collected at the lower end and recirculated. The same nutrient solution was recirculated through both treatments at a flow rate of 150 ml·min-1 through each tray and maintained at a pH of 5.6. Uniform micropropagated `Norland' potato plantlets were transplanted into replicate trays and maintained at 18C, 70% relative humidity, and a continuous photosynthetic photon flux (PPF) of 450 μmol·m-2·s-1. Water tension reduced total plant dry weight, leaf area, leaf number, and stolon number by >75%, but specific leaf weight increased compared to free water. However, tubers enlarged more rapidly with water tension, and plants consistently partitioned a greater fraction of biomass into tubers (than into shoots). Tuber weight was greater with water tension than in the free-water culture in Expt. 1 harvested 37 days after transplanting, however it was less in Expt. 2 when plants were grown to a larger size for 52 days before harvest. Leaf CO2 assimilation rate, stomatal conductance, and transpiration were reduced with water tension, although the relative water content of leaves was not significantly affected. Also, with water tension, concentrations of N, P, Zn, and Cu in leaf tissues decreased, whereas tissue Fe increased compared to plants grown with free water. The results in this study demonstrate that constant water tension significantly affects potato plant growth and shifts biomass partitioning toward tubers.

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Philipp von Bieberstein, Ya-ming Xu, A.A. Leslie Gunatilaka and Raphael Gruener

chamber kept at 28 °C with 16 h of fluorescent lighting. After ≈5 weeks (late summer), seedlings with an aerial length of ≈5 cm were transferred to a float system [deep water culture containing 50% modified Hoagland Nutrient Medium ( Hoagland and Arnon

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Szu-Chin Peng, Iou-Zen Chen and Cheng-Yung Cheng

concentration of oxygen in water medium, bubbling was reported as an applicable method ( Zimmerman, 1930 ). Water culture was suggested as a simple and efficient method for rooting some species’ woody cuttings ( Komissarov, 1968 ). In this study, circulating