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  • Author or Editor: William B. Miller x
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For a number of geophytic crops, pre-plant plant growth regulator (PGR) dips or soaks are an effective method of height control. Previous research has shown that a given PGR solution may be used to dip numerous bulbs without losing efficacy. What has been unknown is whether PGR solutions maintain efficacy over multiple-week (seasonal) time scales, especially if they have previously been used to treat bulbs. To address this question, 30 mg·L−1 flurprimidol solutions were prepared 3 weeks apart and used to dip narcissus and hyacinth bulbs and then held for 4 weeks at 17 °C in darkness. These solutions (now 7 and 4 weeks old) and a freshly prepared solution were used to dip bulbs of eight hyacinth and five narcissus cultivars. After appropriate cooling, bulbs were forced in a greenhouse. Results indicate no difference in growth reduction among the 0-, 4-, or 7-week-old solutions demonstrating no loss of PGR activity over a 7-week period. In two other experiments, 2.5, 5, and 10 mg·L−1 flurprimidol solutions were exposed to 0 to 8 days of full sun (late June) and then used to dip Lilium ‘Tresor’ bulbs for 1 minute. Growth of the plants indicated loss of growth regulation activity (taller plants) as the duration of exposure to sunlight increased, suggesting substantial photolysis of the active ingredient. Together, the results suggest that flurprimidol solutions can be held in darkness at 17 °C and used for at least 7 weeks without loss of efficacy.

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Experiments conducted over 3 years have indicated the efficacy of preplant paclobutrazol or flurprimidol corm soaks for leaf and scape growth control in potted freesia (Freesia hybrida). A range of cultivars subjected to 30- to 60-min soaks in 60 to 120 mg·L−1 paclobutrazol and 10- to 30-min soaks in 10 to 30 mg·L−1 flurprimidol resulted in significant and commercially relevant height control without reducing the number of flowering scapes. Cultivars varied in their response to the plant growth regulators (PGRs), suggesting that individual grower trials will be necessary to develop an optimum treatment for each location.

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Ethylene effects were investigated on two tulip (Tulipa gesneriana L.) cultivars, Markant and Carreria. Pre-cooled bulbs were treated with ethylene (flow-through) for 1 week at 0, 0.1, 1.0, or 10 μL·L−1 (± 10%) in a modified hydroponic system. After ethylene exposure, plants were either destructively harvested for root measurements or forced in a greenhouse for flower measurements. Ethylene exposure at concentrations as low as 1 μL·L−1 during the first week of growth reduced shoot and root elongation and subsequently increased flower bud abortion. At 10 μL·L−1, root growth was essentially eliminated. In a second experiment, bulbs were treated overnight with 1-methylcyclopropene (1-MCP) before a 7-day exposure to 1 μL·L−1 ethylene. 1-MCP pretreatment eliminated the harmful effects of ethylene on root and shoot growth. This study illustrates the effects of ethylene exposure during hydroponic tulip production and demonstrates a potential benefit to treating bulbs with 1-MCP before planting.

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Excised roots of `First Lady' marigold (Tagetes erecta L.) grown in an aerated 0 Fe nutrient solution had Fe(III)-DTPA reductase activity 14-fold greater, and an enhanced ability to acidify the rhizosphere than plants grown in a solution containing 0.018 mm (1 ppm) Fe-DTPA. Reductase activity and rhizosphere acidification of plants grown in 0.018 and 0.09 mm Fe-DTPA were similar. Manganese concentration in leaves of plants grown in the 0 Fe treatment was 2-fold greater than in leaves of plants grown in the 0.018 mm Fe-DTPA treatment. These results indicated that `First Lady' marigold is an Fe-efficient plant that possesses both an inducible or adaptive reductase system and the ability to acidify the rhizosphere, and that these Fe-efficiency reactions do not occur when Fe is sufficient. Chemical name used: ferric diethylenetriaminepentaacetic acid, monosodium salt (Fe-DTPA).

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A necrotic disorder occurs on upper leaves of many oriental hybrid lily (Lilium L.) cultivars, including the most-widely-grown `Star Gazer'. We term this disorder “upper leaf necrosis” (ULN) and hypothesize that it is a calcium (Ca) deficiency. We demonstrated that Ca concentration in necrosed tissues was nearly six-fold below that of normal leaves (0.10% vs. 0.57% dry weight), and that Ca concentration was negatively associated with percentage necrosed leaf area. It was concluded that ULN is a Ca deficiency disorder. When the symptoms were slight, early ULN symptoms appeared as tiny depressed spots on the lower surface of the leaf, or as water-soaked areas when the disorder was severe. Most commonly, ULN began on the leaf margin. The injured areas turned brown, leading to leaf curling, distortion, or tip death. ULN occurred on leaves associated with flower buds and leaves immediately below the flower buds. For the plants grown from 16-18 cm circumference bulbs, the five leaves directly below the flower buds and larger leaves associated with the 1st and the 2nd flower buds were most susceptible. In general, flower buds were not affected by ULN, and continued to develop and flower normally, even though they were associated with subtending, highly distorted leaves. Eighty-five percent of plants began to exhibit ULN symptoms 30-40 days after planting (i.e., 24-34 days after shoot emergence). This was the stage when the 6th or 7th leaf under the bottom flower bud was just unfolded. Light was not the main factor that initiated ULN, however, ULN severity was greatly increased by light reduction, as leaf transpiration was reduced.

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Ethanol was demonstrated to reduce unwanted floral scape and leaf elongation of `Ziva' paperwhite narcissus (Narcissus tazetta) when plants were grown with traditional pebble culture. Root-zone ethanol concentrations of 1% to 5% (v/v) were effective in reducing height without visible phytotoxicity to the roots. Various ethanol sources, including gin, vodka, whiskey, schnapps, rum, and tequila, were equally effective in reducing growth when supplied at 4%; peppermint schnapps caused somewhat more growth inhibition, providing a safe, effective, and organic method for amateurs to control height of this popular flowering bulb. Beer and wine (white or red) were unsuitable for this use at 4% alcohol concentration.

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Irradiating a ferric ethylenediaminetetraacetic acid (FeEDTA)-containing commercially available soluble fertilizer with ultraviolet (UV) and blue radiation from high intensity discharge (HID) lamps caused the photooxidation of the FeEDTA complex, resulting in the loss of 98% of soluble iron. The loss of soluble iron coincided with the development of a precipitate that was mostly composed of iron. The effects of using an irradiated FeEDTA-containing fertilizer solution on plant growth and nutrition under commercial conditions were studied. Application of the irradiated fertilizer solutions to greenhouse grown tomato plants (Lycopersicon esculentum) resulted in lower levels of iron (6%) and zinc (9%), and higher levels of manganese (8%) and copper (25%) in leaf tissue compared to control plants that received a nonirradiated fertilizer solution. Leaf macronutrient levels (phosphorous, potassium, calcium, and magnesium), leaf dry weight, leaf number, and plant height was not affected by application of the irradiated fertilizer solution.

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Postproduction changes in carbohydrate types and quantities in the leaves, stems, and inflorescences of pot chyrsanthemums [Dendranthema × gramfiflorum (Ramat.) Kitamura `Favor'] placed in interior conditions were investigated. Fructans, sucrose, glucose, and fructose were present in all plant parts. In inflorescences and leaves, an additional unidentified substance was present. All plant parts decreased in dry weight during the postproduction evaluation. This decrease was accompanied by overall reductions in total soluble carbohydrates (TSC) and starch. The appearance of leaves and stems was acceptable throughout the experiment. Leaves lost significant amounts of TSC during the first 4 days postproduction (DPP), due primarily to a 76% decrease in sucrose concentration. After 4 DPP, leaf and stem TSC remained relatively unchanged. In inflorescences, petal expansion continued through 12 DPP. Visible signs of senescence, including loss of turgor, color changes, and inrolling of petal edges were observed at 20 DPP, and by 28 DPP, the plants were determined unacceptable for consumer use. Inflorescences increased in fresh weight, but not dry weight, during petal expansion, then each decreased. Inflorescence TSC fell from 146 mg.g-1 dry weight at O DPP to 11 mg.g-1 at 28 DPP. Reducing sugars accounted for 84% of the inflorescence TSC at 4 DPP, dropping to 48% at 28 DPP. Fructan concentration decreased through 16 DPP and then remained unchanged, while starch levels rose from 25 to 34 mg·g -1 dry weight through 12 DPP, then decreased. Fractans decreased in polymerization during petal expansion. This result suggests an alternate use of fructans and starch as pools of available reserve carbohydrate during petal expansion in chrysanthemum.

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Abstract

All growth retardant treatments (ancymidol, 50 mg·liter−1, one or two sprays; uniconazole, 5, 10, or 15 mg·liter−1, one or two sprays; 20 mg·liter−1, one spray) reduced Easter lily (Lilium longiflorum Thunb.) plant heights when compared to controls. Plant heights decreased linearly with increasing concentration of uniconazole for both one- and two-spray treatments. High concentrations of uniconazole delayed anthesis; ancymidol treatments did not. Individual corolla length was not affected by treatments. Treatments did not affect daughter bulb depletion or new daughter bulb growth. Total leaf area and leaf dry weight decreased as uniconazole concentration increased; ancymidol treatments did not affect leaf area, but did reduce leaf dry weight. Leaf total soluble carbohydrate decreased with increasing concentration of uniconazole. Chemical names used: α-cyclopropyl-α-(4-methoxyphenyl)-5-pyrimidine-methanol (ancymidol); (E)-1-(p-chlorophenyI)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-1-penten-3-ol (uniconazole).

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Upper leaf necrosis (ULN) on Lilium `Star Gazer' has been recently demonstrated to be a calcium (Ca) deficiency disorder. In the current studies, we confirmed this by using a Ca-free nutrient regime to reproduce ULN symptoms. The ability of a bulbous storage organ to supply calcium to a growing shoot is poorly understood. Therefore, we conducted experiments to determine Ca partitioning during early growth stages, and under suboptimal Ca levels to determine how the bulb affects the symptomatology. The results indicated that ULN is originally caused by an insufficient Ca supply from the bulb. In the most susceptible period, bulb dry matter decreased dramatically and Ca concentrations in immature folded leaves dropped to very low levels. Consequently, necrosis began to appear on the upper, young leaves. The bulb was able to supply Ca to other organs, but only to a limited extent since Ca concentration in bulbs was low (0.04% w/w). To confirm this result, we cultivated lilies with low-Ca or Ca-free nutrient solution and obtained bulbs with extremely low internal Ca concentrations. Upon forcing these low-Ca bulbs, we found, as expected, prominent necrosis symptoms on the lower and middle leaves. Data suggested the lower and middle leaves relied more on Ca supplied from the bulb, while upper leaves and flowers relied more on Ca uptake from the roots. Different organs have different Ca requirements, and tissue sensitivity to Ca deficiency varies according to the growth stage.

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