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Matthew D. Taylor, Paul V. Nelson and Jonathan M. Frantz

Sudden pH decline (SPD) describes the situation where crops growing at an appropriate pH rapidly (within 1–2 weeks) cause the substrate pH to shift downward one to two units. ‘Designer Dark Red’ geraniums (Pelargonium ×hortorum Bailey) were grown in three experiments to assess possible effects of temperature on SPD. The first experiment tested the effect of four day/night temperature regimes (14 °C day/10 °C night, 18 °C day/14 °C night, 22 °C day/18 °C night, and 26 °C day/22 °C night) on substrate acidification. At 63 days after transplanting (DAT), substrate pH declined from 6.8 to 4.6 as temperature increased. Tissue phosphorus (P) of plants grown at the highest three temperatures was extremely low (0.10%–0.14% of dry weight), and P stress has been reported to cause acidification. It was not possible to determine if the drop in substrate pH was a singular temperature effect or a combination of high temperature and low P. To resolve this, a second experiment tested a factorial combination of the three highest temperatures from the first experiment and five preplant P rates (0, 0.065, 0.13, 0.26, or 0.52 g·L−1 substrate). Regardless of tissue P concentrations, which ranged from deficient to above adequate, substrate pH decreased with increasing temperature. At 63 DAT, in the 0.065 and 0.13 P treatments, tissue P was deficient and pH decreased with increasing temperature from 5.6 to 4.7 and 5.9 to 4.7, respectively. In the 0.26 P treatment, tissue P was adequate at the lowest temperature and there was no acidification. At the mid- and highest temperatures, tissue P was deficient and statistically equivalent, yet pH decreased to 5.2 and 4.7, respectively. In the highest P treatment, tissue P levels were unaffected by temperature, above adequate, and pH declined with each increase in temperature from 6.5 to 5.0. The results at 63 DAT once more showed that temperature acted independent of tissue P and caused geraniums to acidify the substrate. In the third experiment, the amount of acidity produced by roots of plants grown at the two highest temperatures used in the first two experiments was quantified. Plants grown at the higher temperature produced 28% more acid per gram dry root. The results herein indicate that high temperature can induce SPD by geranium.

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James D. Spiers, Fred T. Davies, Scott A. Finlayson, Chuanjiu He, Kevin M. Heinz and Terri W. Starman

This research focused on the effects of nitrogen fertilization on jasmonic acid accumulation and total phenolic concentrations in gerbera. The phytohormone jasmonic acid is known to regulate many plant responses, including inducible defenses against insect herbivory. Phenolics are constitutive secondary metabolites that have been shown to negatively affect insect feeding. Gerbera jamesonii `Festival Salmon Rose' plants were grown in a growth chamber and subjected to either low fertilization (only supplied with initial fertilizer charge present in professional growing media) or high fertilization (recommended rate = 200 mg·L-1 N). Plants were fertilized with 200 mL of a 15N–7P–14K fertilizer at 0 or 200 mg·L-1 N at each watering (as needed). Treatments consisted of ±mechanical wounding with a hemostat to one physiologically mature leaf and the subsequent harvest of that leaf at specified time intervals for jasmonic acid quantification. Total phenolics were measured in physiologically mature and young leaves harvested 0 and 10 hours after ±mechanical wounding. Low-fertility plants had reduced aboveground dry mass, were deficient in nitrogen and phosphorus, and had about a 10× higher concentration of total phenolics when compared to high fertility plants. In low-fertility plants, young leaves had greater concentrations of phenolics compared to physiologically mature leaves. There were no differences in total phenolics due to wounding. The effect of nitrogen fertilization on jasmonic acid accumulation will also be discussed.

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Stephen L. Love, Thomas Salaiz, Bahman Shafii, William J. Price, Alvin R. Mosley and Robert E. Thornton

Ascorbic acid (vitamin C) is an essential nutrient in the human diet and potatoes are a valuable source. As a first step in breeding for potatoes (Solanum tuberosum L.) with higher levels of ascorbic acid, 75 clones from 12 North American potato-breeding programs were evaluated for concentration, and 10 of those for stability of expression. Trials were grown in Idaho, Oregon, and Washington in 1999 and 2000, tubers sampled, and ascorbic acid quantified. There were significant differences among clones and clone by environment interaction was also significant. Concentration of ascorbic acid of the clones was continuously distributed over a range of 11.5 to 29.8 mg/100 g. A subgroup of 10 clones was analyzed using an additive main effects and multiplicative interaction (AMMI) model, to diagnose interaction patterns and measure clone stability. The first two principal component axes accounted for over 80% of the variability. Bi-plot analysis showed `Ranger Russet' to be highly unstable across the environments tested. A plot of Tai's stability statistics found six of the 10 clones to be stable for ascorbic acid expression. Appropriate evaluation methods for ascorbic acid concentration must involve multi-year testing.

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Tripti Vashisth, Mercy A. Olmstead, James Olmstead and Thomas A. Colquhoun

then 1 g fresh weight (FW) of fine powder was mixed with 1 mL deionized water at room temperature. Clear supernatant was removed from each sample after centrifugation and citric and L-malic acid quantification was done as per manufacturer’s instructions

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Justine E. Vanden Heuvel, Steven D. Lerch, Celine Coquard Lenerz, James M. Meyers and Anna Katharine Mansfield

asked to smell all the samples before indicating aroma preference by ranking wines from one (most favored) to four (least favored). Wines were not ranked for gustatory properties, as sensory screening and chemical analysis including acid quantification

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Jessica L. Gilbert, Michael L. Schwieterman, Thomas A. Colquhoun, David G. Clark and James W. Olmstead

blueberry samples from the volatile collection step were immediately frozen at –80 °C for sugar and acid quantifications. When sugar and acid measurements were to take place, the samples were defrosted overnight at 4 °C and then allowed to rise to room

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Rafael Urrea-López, Rocío I. Díaz de la Garza and Juan I. Valiente-Banuet

186001344; Milford, MA) with an isocratic elution using a phosphate buffer (200 m m ; pH 2.4) as the mobile phase. Ascorbic acid quantification was estimated at 244 nm using calibration curves made with an ascorbic acid standard (Sigma-Aldrich, St. Louis, MO

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M. Joseph Stephens, Peter A. Alspach, Ron A. Beatson, Chris Winefield and Emily J. Buck

95% at 13.8 min, and staying at that concentration until the end of the run at 15 min. Sample injections were 10 μL of centrifuged juice, diluted if necessary with aqueous 1% formic acid. Quantification of anthocyanins was carried out at 520 nm, in

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T. Casey Barickman, Dean A. Kopsell and Carl E. Sams

through a 0.45-µm nylon syringe filter and collected in a 2-mL HPLC vial for analysis. Separation parameters and organic acid quantification were carried out with authentic standards using an Agilent 1200 series HPLC with a refractive index detector

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Zhongchun Jiang, Chenping Xu and Bingru Huang

amino acid quantification J. Food Compost. Anal. 19 112 117 Teixeira, J. Fidalgo, F. 2009 Salt stress affects glutamine synthetase activity and mRNA accumulation on potato plants in an organ-dependent manner Plant Physiol. Biochem. 47 807 813 Turano, F