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Christine Yung-Ting Yen, Terri W. Starman, Yin-Tung Wang, Andreas Holzenburg, and Genhua Niu

Hybrids of Dendrobium nobile Lindl. have high potential to become a high-value pot plant, but detailed research to support the development of commercial production protocols was lacking. A 3 × 5 factorial experiment was conducted to investigate the effects of nutrient termination date (1 Aug., 1 Sept., or 1 Oct.) and nutrient reapplication time (at the beginning or in the middle of cooling, immediately after or 2 weeks after the completion of cooling, or no nutrient reapplication) on growth and flower development of Dendrobium Sea Mary ‘Snow King,’ a D. nobile hybrid. Interaction between nutrient termination date and reapplication time on growth and flowering was nonsignificant for all variables measured, and reapplication time had only a minor effect on leaves remaining. Regardless of nutrient reapplication time, delaying nutrient termination date resulted in improved growth and flowering. Nutrient termination on 1 Oct. resulted in taller plants with more nodes, leaves remaining, flowering nodes, and total flowers as well as fewer aborted flowers than an earlier termination date. Nutrient supply until 1 Oct. did not lead to differences in time required for anthesis but extended the time needed to reach full flowering by 1.5 d. The results suggest that flower development benefited more from the nutrients that were accumulated in mature pseudobulbs before nutrient termination rather than from those being taken from the reapplied fertilizers. Only lateral buds protruding 2 mm or more from the pseudobulb surface showed differentiated floral structures when examined histologically. The buds, excised 4 weeks after cooling treatments began, showed that nutrient termination on 1 Aug. resulted in larger flower primordia than those ended on 1 Oct., indicating an earlier or faster flower differentiation with earlier nutrient termination. No aerial shoot formation or reversion of reproductive to vegetative buds arose as a result of either late nutrient termination or resumption of nutrient application.

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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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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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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.