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Susan S.C. Liou and William B. Miller

During transportation and storage of Dutch tulip bulbs, potential ethylene exposure could lead to flowering abnormalities, including accelerated flowering, shortened plant heights, and in the most extreme case, flower abortion. Sources of ethylene include Fusarium-infected bulbs, deteriorating tissues, and combustion engines. Treatment with 1-MCP (1-methylcyclopropene) may prevent ethylene action as 1-MCP occupies ethylene specific receptors on target tissue. Two aspects of this problem were quantified using four tulip cultivars: duration of ethylene exposure necessary to induce damage as well as the effective period of protection by 1-MCP against ethylene. Flower abortion appeared in susceptible cultivars after ≥9 days of ethylene exposure (10 ppm) and was only found in mature bulbs (late November). The effective protection period of 1-MCP against ethylene (2-week exposure of 10 ppm) was determined, using flowering percentages, to be as long as 4–7 days in young bulbs and 28 days for older bulbs. Effects of ethylene on other flower attributes and implications of these findings in industry practices will be discussed.

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William B. Miller and Madeline W. Olberg

Ethephon [(2-chloroethyl) phosphonic acid] is a plant growth regulator (PGR) that releases ethylene following application. Although ethephon is commonly used as a foliar spray during the commercial production of ornamental crops, including spring bulb crops such as daffodil (Narcissus pseudonarcissus L.), there has been increased interest in using ethephon as a root-zone-applied PGR. In this work, we evaluated a number of factors important for the development of ethephon as a soil drench for daffodil. Results indicate that a given dose (milligrams ethephon per pot) could be applied in volumes ranging from 15 to 120 mL (per 15-cm pot) with equal efficacy. Similarly, the same dose of ethephon could be applied as a foliar/substrate surface spray with volume of 105 to 525 mL·m−2 with equal efficacy. Although the efficacy of ethephon drenches interacted with forcing temperature, drenches were nonetheless effective across the range of temperatures commonly used for daffodil production. Plant size at the time of ethephon application had no effect on final plant size (at flower senescence). The rate of ethylene release from a peat-based substrate was highly temperature dependent, and ethephon was readily leached from this same substrate.

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Susan S.C. Liou* and William B. Miller

Tulip bulbs are produced in the Netherlands and are shipped to United States during the months of July and August in temperature-controlled shipping containers. Each shipment is often composed of a mixture of many cultivars. Mechanical failure of temperature controls may result in high temperatures that ultimately may reduce forcing quality of the bulbs. When such accidents occur, an immediate decision must be made about whether to invest more time and money on these potentially damaged bulbs. Such a decision is not easy because symptoms of heat damage are often delayed until months later. Research on a single cultivar, `Apeldoorn', has shown that heat stress can cause flower abortion and other abnormalities. However, cultivars undoubtedly vary in their response to heat stress. Thus in the 2002 and 2004 forcing seasons, ≈45 cultivars were screened for response to a standard heat stress of 4 days at 35 °C. Prior to the heat stress, bulbs were held at 17 °C or 9 °C for 4 weeks, mimicking conditions used for late and early forced bulbs, respectively. Flower and leaf height, percent flower abortion, and flowering date were evaluated. Heat stress caused flower abortion and reduced plant height in sensitive cultivars. Across all cultivars, cold storage prior to the heat stress significantly increased bulb's sensitivity to heat stress. Using percent flower abortion, cultivars were grouped into three categories: resistant, moderate, and susceptible. With this information, we hope that damage assessment may become easier and fewer bulbs wasted.

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Hye-Ji Kim and William B. Miller

The effect of GA4+7 plus benzyladenine (BA) on postproduction quality was investigated in `Seadov' tulips (Tulipa gesneriana). Potted tulips at half-colored bud stage or full-bloom stage were sprayed with a range of GA4+7 plus BA, and placed in a simulated consumer environment (SCE) in order to determine effectiveness of the compound at each stage. Regardless of plant stage, treatment with GA4+7 plus BA effectively improved individual flower longevity and whole plant longevity in the range of concentrations tested. GA4+7 plus BA had a strong effect on enhancing flower longevity when sprayed to mature (fully colored) buds, and a lesser effect on immature (green) buds, and whole plant longevity increased with higher doses of GA4+7 plus BA. When applied to open flowers, however, concentrations over 50 mg·L–1 reduced individual flower and whole plant longevities relative to lower concentrations resulting from unwanted full-opening of older flowers and exaggerated gynoecium growth. Concentrations as low as 10 mg·L–1 significantly increased longevity of tulip flowers of all age classes. The effects of enhancing postproduction quality of `Seadov' pot tulips were primarily derived from the BA component of the compound.

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Joseph P. Albano and William B. Miller

We have shown previously that Fe-chelates incorporated into soluble fertilizers are vulnerable to photodegradation, and that such solutions can cause modifications in root reductase activity. The objective of this research was to determine the effects of Fe-chelate photodegradation under commercial production conditions. Marigolds were grown in a greenhouse and transplanted stepwise from #200 plug trays to 804 packs to 11.4-cm (4.5-inch) pots. Plants were harvested at the end of each stage, and treatments consisted of either irradiated (complete loss of soluble Fe) or non-irradiated fertilizer solutions ranging from 100-400 mg/L N (0.5–2 mg/L Fe). In the plug and pack stages, foliar Fe was significantly lower and Mn significantly higher in plants treated with the irradiated than nonirradiated fertilizer solutions, averaging 97 μg·g–1 and 115 μg·g–1 Fe, and 217 μg·g–1 and 176 μg·g–1 Mn, respectively. Fe(III)-DTPA reductase activity of roots of plugs treated with the irradiated fertilizer solution was 1.4-times greater than for roots treated with the non-irradiated fertilizer solution. Leaf dry weight in the plug and pack stages was not affected by treatment, and averaged 0.1 g and 1.2 g per plant, respectively.

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Michael R. Mason and William B. Miller

Interactions of ethephon and irradiance reduction were investigated in terms of flower bud blasting in Easter lily (Lilium longiflorum Thunb. `Nellie White'). Silver thiosulfate (STS) was investigated as an inhibitor of ethylene-induced bud abortion. Fourteen days of 92% irradiance reduction significantly increased bud abortion when plants were exposed to 2.1 mm ethephon. Bud abortion was 39% and 60% for plants grown in ambient and reduced irradiance, respectively. Silver thiosulfate was applied to plants 2 or 3 weeks after the date of the first visible bud, followed by ethephon treatment 2 days later. Bud abortion was significantly reduced by 1 or 2 mm STS, without phytotoxicity. Pretreatment with 1 or 2 mm STS as early as 4 weeks before ethephon exposure significantly reduced ethephon-induced bud abortion. Silver thiosulfate application could inexpensively reduce flower bud abortion during latter stages of greenhouse forcing of Easter lilies.

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Joseph P. Albano and William B. Miller

The susceptibility of seven African marigold (Tagetes erecta L.) cultivars to iron toxicity was assessed. Plants were grown in a greenhouse in a soilless medium and Fe-DTPA was incorporated into the nutrient solution at either 0.018 mmol·L-1 (low) or 0.36 mmol·L-1 (high). Symptoms of Fe toxicity (bronze speckle disorder in marigold characterized by chlorotic and necrotic speckling and downward leaf cupping and curling) developed only in the high-Fe treatment. The concentration of Fe in leaves in the high-Fe treatment was 5.6 and 1.7 times as great as in the low-Fe treatment for `Orange Jubilee' and `Discovery Orange', respectively. Based upon the percentage of plants affected and leaf symptom severity, relative cultivar susceptibility to Fe toxicity was Orange Jubilee > First Lady > Orange Lady > Yellow Galore > Gold Lady > Marvel Gold > Discovery Orange. Chemical names used: ferric diethylenetriaminepentaacetic acid, disodium salt dihydrate (Fe-DTPA).

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Anil P. Ranwala and William B. Miller

The effects of Promalin® [PROM; 100 mg·L–1 each of GA4+7 and benzyladenine (BA)] sprays on leaf chlorosis and plant height during greenhouse production of ancymidol-treated (two 0.5-mg drenches per plant) Easter lilies (Lilium longiflorum Thunb. `Nellie White') were investigated. Spraying with PROM at early stages of growth [36 or 55 days after planting (DAP)] completely prevented leaf chlorosis until the puffy bud stage, and plants developed less severe postharvest leaf chlorosis after cold storage at 4 °C for 2 weeks. When PROM was sprayed on plants in which leaf chlorosis had already begun (80 DAP), further leaf chlorosis was prevented during the remaining greenhouse phase and during the postharvest phase. PROM caused significant stem elongation (23% to 52% taller than controls) when applied 36 or 55 DAP, but not when applied at 80 DAP or later. The development of flower buds was not affected by PROM treatments. Although PROM sprays applied at 55 DAP or later increased postharvest flower longevity, earlier applications did not. Chemical names used: N-(phenylmethyl)-1H-purine 6-amine (benzyladenine, BA); α-cyclopropyl-α-(p-methoxyphenyl)-5-pyrimidinemethanol (ancymidol).

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Joseph P. Albano and William B. Miller

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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Joseph P. Albano and William B. Miller

Irradiation of, ferric ethylenediaminetetraacetic acid (FeEDTA, iron chelate)-containing commercial fertilizer solutions by fluorescent plus incandescent lamps resulted in the loss of both FeEDTA and soluble iron (Fe), and the formation of a yellow-tan precipitate that was mostly composed of Fe. The ratio of soluble Fe:manganese (Mn) was altered due to FeEDTA photodegradation from 2:1 in the nonirradiated solutions to 1:4 in the irradiated solutions, respectively. Storing fertilizer solutions in containers that were impervious to light prevented FeEDTA photodegradation.