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Moritz Knoche, Norman K. Lownds, and Martin J. Bukovac

Effect of carrier volume (range 119 to 668 L·ha-1) on dose response relationships of daminozide and GA3 was investigated using bean (Phaseolus vulgaris L.) seedlings as a model system. Carrier volume was varied by altering nozzle travel speed thereby maintaining constant flow rate and droplet size. Response was indexed by inhibition (daminozide) or stimulation (GA3) of elongation of first plus second internodes above primary leaves 14 days after spray application. Increasing dose by increasing concentration and/or increasing carrier volume at constant concentration increased response. For a given dose retained, response to daminozide was related positively to carrier volume, while GA3 response was not affected. Chemical names used: butanedioic acid mono(2,2-dimethylhydrazide) (daminozide); gibberellic acid (GA3).

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A.J. Bishko and P.R. Fisher

Our objective was to systematically quantify the dose response from applications of several basic materials recommended for raising pH in acidic media. A peat (70%)/perlite (30%) medium was mixed with a pre-plant nutrient charge, a wetting agent, and 0, 0.3, 0.6, 0.9, 1.2, or 1.5 kg dolomitic hydrated lime/m3, resulting in a range in initial pH from 3.4 to 6.4. Five rates of flowable dolomitic limestone, five rates of potassium bicarbonate, two rates of potassium hydroxide, a supernatant of calcium hydroxide and a distilled water control were applied as single drenches. The medium was irrigated with distilled water when it dried to 50% container capacity as determined by weight. Media pH and EC of four replicates were tested at 1 day and 1, 2, 3, and 4 weeks after application as a saturated media extract. Flowable limestone and potassium bicarbonate both significantly raised medium pH by up to 2 units compared with the control, depending on concentration. As initial medium pH increased, the effect of the basic chemicals on medium pH decreased. For example, flowable lime applied at 0.5 L·100 L–1 of distilled water increased pH by 2 units at an initial medium pH of 3.4 and by 0.4 units at an initial pH of 6.4. Potassium hydroxide and calcium hydroxide drenches did not significantly raise pH. Potassium bicarbonate was easier to apply than the suspension of flowable limestone, however both chemicals provide practical methods for raising pH of soilless media.

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Brian K. Maynard and Nina L. Bassuk

Three experiments were undertaken to examine the effect of stockplant etiolation, shading, and stem banding, prior to cutting propagation, on the auxin dose-response of rooting in stem cuttings of Carpinus betulus `fastigiata'. A 2 × 2 factorial of etiolation and banding utilized stockplants forced in a greenhouse, etiolated for 1 week and banded with Velcro™ for 1 month. In a separate study shading was applied up the time of harvesting cuttings. IBA was applied to cuttings as an aqueous ethanol quick dip in concentrations ranging from 0 to 80 mM. Rooting percentage and number were best described, up to a peak response, by a linear function proportional to the logarithm of applied IBA. The inhibition of rooting by supra-optimal IBA was directly proportional to IBA concentration. Cuttings prepared from shoots which had been etiolated or banded rooted better at low IBA and at their respective optimal IBA levels. Cuttings from shoots receiving both etiolation and banding yielded higher rooting percentages and more roots per rooted cutting on average. Etiolation and banding served to increase both initial and maximum rooting capacities, and to reduce the sensitivity of cuttings to supraoptimal auxin-induced inhibition of adventitious root initiation. The auxin dose-response interacted with shading to yield the best rooting at 95% shade and 3.7 mM IBA.

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Deniz İnci, Liberty Galvin, Kassim Al-Khatib, and Ahmet Uludağ

% during the night. Seedling emergence was ≈35% to 45% for all populations; once the cotyledons reached 1 cm in height, plants were thinned to one plant per cell and uniform plants were selected for the dose response study. Plants were irrigated daily to

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P.R. Fisher, R.D. Heins, and J.H. Lieth

Stem elongation response to a single foliar application of the growth retardant chlormequat chloride [(2-chloroethyl) trimethylammonium chloride] for poinsettia (Euphorbia pulcherrima Klotz.) was quantified. Growth retardant applications did not affect final leaf count or timing of visible bud, first bract color, or anthesis. There was a statistically significant effect of growth retardant concentration on stem elongation, with a range from 289 ± 15 mm (mean 95% confidence intervals) for the control plants to 236 ± 17 mm at 4000 ppm. The growth-retarding effect during the first day after the application was not significantly different between 500 and 4000 ppm, and concentration primarily affected the duration of growth-retarding activity. A dose response function was incorporated into a three-phase mathematical function of stem elongation of single-stem poinsettia to predict elongation of treated and untreated plants. The model was calibrated using a data set from plants receiving 0, 500, 1000, 1500, 2000, 3000, and 4000 ppm, with a resulting R 2 of 0.99. Validation of the dose response model against an independent data set resulted in an r 2 of 0.99, and predicted final stem length was within 12 mm of observed final length.

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David Bubenheim, Kanapathipillai Wignarajah, Wade Berry, and Theodore Wydeven

Recycling wastewater containing soaps and detergents for plant growth is highly desirable when fresh water is limited. This is especially true during times of drought and is imperative in some specialized situations such as a regenerative space habitat. To regenerate food, water, and air, the National Aeronautics and Space Administration's Controlled Ecological Life Support System (CELSS) must recycle wastewater commonly known as gray water. The anionic surfactant Igepon is the principal ingredient of many detergent formulations and soaps and is a prime candidate for use in a space habitat. To determine if gray water would have phytotoxic effects on crops grown in a CELSS, `Waldmann's Green' lettuce (Lactuca sativa L.) was grown in nutrient solutions containing varying concentrations of Igepon TC-42. Igepon concentrations of 250 mg·L-1 or higher in nutrient solutions resulted in phytotoxic effects in lettuce. Thus, the toxic threshold of Igepon is <250 mg·L-1. Toxicity symptoms include browning of the roots within 4 hours of exposure to Igepon followed by suppression of root dry mass within 24 hours. Plant death never resulted from exposure to Igepon used in these experiments, although roots were killed. The phytotoxic effect of Igepon was not persistent; plants initially displaying acute toxicity show clear signs of recovery within 3 days of initial exposure. Further, when fresh plants were exposed to these same nutrient solutions 3 days or more following initial Igepon addition, no phytotoxic effect was observed. The elimination of the phytotoxicity was associated with a decrease in fatty acid components in the nutrient solution associated with Igepon. The degradation of phytotoxicity appears to be associated with microbes present on the surface of the roots and not directly due to any plant process or instability of the surfactant.

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Barbara J. Daniels-Lake and Robert K. Prange

2 only when ethylene was also present, and a dose–response to CO 2 when the gases were applied together ( Fig. 1 ). Table 1. Fry color of potatoes stored with CO 2 and/or ethylene gas for 9 weeks, means of 2006 and 2007 data. Fry color was

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Giovanni A. Caputo, Phillip A. Wadl, Lambert McCarty, Jeff Adelberg, Katherine M. Jennings, and Matthew Cutulle

sweetpotato clones and 2) characterize the response of ‘Beauregard’ to bentazon and exogenous applications of melatonin. Materials and Methods Cultivar dose response. A study was conducted at the Clemson University Coastal Research and Education Center in

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Dennis C. Odero, Jose V. Fernandez, and Nikol Havranek

to determine the efficacy of soil-applied preemergence S -metolachlor on weed control and radish tolerance on organic soils of the EAA using a dose–response bioassay. Materials and Methods Field studies were conducted at the Everglades Research and

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Po-Lung Chia and Chieri Kubota

flux) as well as the spectral quality of light, understanding phytochrome kinetics (or dose–response) would help in selecting the necessary light intensity, quality, and treatment duration. Such understanding is especially important in horticultural