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C. Olivella, C. Biel, R. Savé, and M. Vendrell

The effects of flooding (3 days) and recovery (3 days) on leaf gas exchange parameters (stomatal conductance, net photosynthetic assimilation rate, and leaf transpiration rate) were studied in five, 1-year-old gerbera (Gerbera jamesonii Bolus) cultivars under greenhouse conditions. Flooding reduced the measured parameters in all cultivars, which had not recovered 3 days after flooding ceased. A more detailed study was conducted with the `Beauty' cultivar, in which leaf water potential (Ψw); root hydraulic resistance (Rh); and hormonal concentrations of ABA, IAA, and CK were measured in leaves and roots. Plants were flooded for 2 days, then allowed to recover for 4 days. After 2 days of flooding, Ψw had decreased and Rh had increased. Leaf ABA content increased and IAA and CK content decreased from the start of flooding and did not change during recovery. In roots a transient increase in root ABA levels occurred during flooding and a sharp decrease was measured during recovery, which was related to root death. Similar patterns were observed in root CK concentrations. The IAA concentration in roots remained constant throughout the experiment. The results suggest that ABA and CK may act as signals of flooding stress. Also, the marked intolerance of gerbera to flooding could be a serious barrier to its culture under anaerobic conditions, and hence careful irrigation management is required. Chemical names used: abscisic acid (ABA); indoleacetic acid (IAA); cytokinin (CK).

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Farzad Nazari and Mahmoud Koushesh Saba

) Intl. J. Hort. Sci. Technol. 1 61 77 Balestra, G.M. Agostini, R. Bellincontro, A. Mencarelli, F. Varvaro, L. 2005 Bacterial populations related to gerbera ( Gerbera jamesonii L.) stem break Phytopathol. Mediterr. 44 291 299 Burt, S. 2004 Essential oils

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Julie A. McIntyre, Douglas A. Hopper, and W.S. Cranshaw

Chemical and physical methods were tested to determine their effectiveness in controlling Western Flower Thrips, Frankliniella occidentalis (Pergande), in greenhouses. Comparisons were made between abamectin (Avid); Spinosyn A and D, formulated from the soil Actinomycete, Saccharopolyspora spinosa (Spinosad); azadirachtin (Margosan-O); and diatomaceous earth, a physical control aimed at deterring pupation. Results based on the number of thrips counted in gerbera (Gerbera jamesonii L.) flowers indicate that the chemical treatments were significantly more effective in reducing populations than the diatomaceous earth. Over time, the population of thrips in both the Avid and Spinosad treatments was reduced to zero. Diatomaceous earth treatments reduced populations almost 50% as compared to the control, while reductions from Margosan-O ranged 50-90%.

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Wouter G. van Doorn and Yke de Witte

Including bacteria in the vase water of cut Gerbera jamesonii Bolus flowers resulted in an increase in scape curvature depending on the concentration of bacteria in the water, cultivar, and season. In the summer, a strain of Pseudomonas aeruginosa or a mixed population of bacterial species, all isolated from the vase water of cut gerbera flowers, resulted in curvature of >90° in `Liesbeth' at 108 cfu/ml and in `Mickey' at 1010 cfu/ml. In winter, the lowest bacterial concentrations that resulted in such bending were 106 and 108 cfu/ml, respectively. `Mickey' showed bending at a lower water potential than `Liesbeth'. Comparison between these results and the bacterial counts in vase water and water at retail shops indicates that frequently observed scape bending is at least partly due to bacteria.

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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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James D. Spiers, Fred T. Davies, Chuanjiu He, Carlos Bogran, Amanda Chau, Kevin M. Heinz, and Terri W. Starman

This research focused on the influence of insecticides on gas exchange, chlorophyll content, vegetative and floral development, and overall plant quality of gerbera (Gerbera jamesonii var. `Festival Salmon'). Insecticides from five chemical classes were applied weekly at 1× and 4× the recommended concentrations. Insecticides used were: abamectin (Avid® 0.15 EC), acephate (Orthene® Turf, Tree & Ornamental Spray 97), bifenthrin (Talstar® Nursery Flowable), clarified hydrophobic extract of neem oil (Triact® 70), and spinosad (Conserve® SC). Phytotoxicity occurred in the form of leaf chlorosis on all acephate treatments, with the greatest damage occurring at the 4× concentration. Photosynthesis and stomatal conductance were significantly reduced in plants treated with neem oil extract. Plants treated with the neem oil extract (1× and 4×) flowered later and had reduced growth [lower shoot dry mass (DM) and total DM]. Plants that received 4× the recommended concentration of neem oil extract had reduced leaf area, thicker leaves (lower specific leaf area), higher leaf chlorophyll content, and reduced flower production, as determined by flower number and flower DM. Plants treated with acephate 4× concentration were the lowest quality plants due to extensive phytotoxicity (leaf burn), which also reduced photosynthesis. The highest quality plants were treated with spinosad and abamectin due to zero phytotoxicity and/or no thrips damage (thrips naturally migrated into the greenhouse). The control plants and plants treated with bifenthrin 1× were not marketable due to thrips damage; however, plant growth characteristics and gas exchange were not statistically different.

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R. Savé, J. Peñuelas, I. Filella, and C. Olivella

One-year-old gerbera plants subjected to 1 night at 5C had reduced leaf water losses and chlorophyll content and increased root hydraulic resistance, but stomatal conductance and leaf water potential did not change. After 3 nights, leaf water potential had decreased and leaf reflectance in the visible and the near-infrared had increased. Similarly, abscisic acid (ABA) in leaves had increased and cytokinins (CK) in leaves and roots had decreased, but ABA levels in roots did not change. After 4 days at 20C, root hydraulic resistance, reflectance and leaf water loss returned to their initial values, but leaf water potential and chlorophyll content remained lower. Leaf ABA levels reached values lower than the initial, while root ABA and leaf CK levels retained the initial values. These data suggest that in the gerbera plants studied, 3 nights at 5C produced a reversible strain but otherwise plants remained uninjured, so this gerbera variety could be cultured with low energetic inputs under Mediterranean conditions. The results may indicate that ABA and CK were acting as synergistic signals of the chilling stress. Spectral reflectance signals seemed to be useful as plant chilling injury indicators at ground level.

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James D. Spiers, Fred T. Davies Jr., Chuanjiu He, Carlos E. Bográn, Kevin M. Heinz, Terri W. Starman, and Amanda Chau

This study evaluated the influence of insecticides on gas exchange, chlorophyll content, vegetative and floral development, and plant quality of gerbera (Gerbera jamesonii Bolus `Festival Salmon'). Insecticides from five chemical classes were applied weekly at 1× or 4× their respective recommended concentration. The insecticides used were abamectin (Avid), acephate (Orthene), bifenthrin (Talstar), clarified hydrophobic extract of neem oil (Triact), and spinosad (Conserve). Photosynthesis and stomatal conductance were reduced in plants treated with neem oil. Plants treated with neem oil flowered later—and at 4× the recommended label concentration had reduced growth, based on lower vegetative dry mass (DM) and total aboveground DM, reduced leaf area, thicker leaves (lower specific leaf area), higher chlorophyll content (basal leaves), and reduced flower production. Plants treated with acephate at 4× the recommended label concentration were of the lowest quality due to extensive phytotoxicity (leaf chlorosis). Plants treated with 1× or 4× abamectin or spinosad were of the highest quality due to no phytotoxicity and no thrips damage (thrips naturally migrated into the greenhouse). The control plants and plants treated with 1× bifenthrin had reduced quality because of thrips feeding damage; however gas exchange was not negatively affected.

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Devin L. Radosevich, Raymond A. Cloyd, and Nathan J. Herrick

Entomological and Prairie Arthropod Research (Manhattan, KS). Plant material and procedures Yellow transvaal daisy, Gerbera jamesonii , cut flowers were obtained from a wholesale broker (Koehler & Dramm of Missouri, Kansas City, MO) and used in a series of

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Leah L. Granke, Layla E. Crawford, and Mary K. Hausbeck

Michigan ranks fifth in potted gerbera daisy ( Gerbera jamesonii H. Bolus) production after Texas, California, Illinois, and Florida and also produces a limited number of gerbera daisies for cut flowers. Potted gerbera production represents a $730