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Polyxeni M. Filios and William B. Miller

We conducted a series of studies to determine the efficacy of a sprayable formulation of 1-methylcyclopropene (1-MCP; AFxRD-038) to inhibit ethylene-mediated flower abscission in Impatiens walleriana. Exposing Impatiens plants to 1.0 μL·L−1 ethylene for 18 hours caused complete abscission of open flowers and most buds. Sprays of the novel 1-MCP formulation at concentrations >2.5 mg·L−1 protected plants from ethylene. At 5 and 10 mg·L−1, the efficacy of 1-MCP increased as spray volume increased from 102 mL·m−2 to 306 mL·m−2. 1-MCP was rainfast with no decrease in efficacy resulting from heavy overhead irrigation within 1–2 minutes of application. Prepared 1-MCP solutions (10 mg·L−1) remained effective up to 2 weeks after mixing if held in airtight containers. The sprayable 1-MCP formulation provided protection against exogenous ethylene for a maximum of 4 days and reduced stress-related abscission from 3 days of darkness (in the absence of exogenous ethylene) at 20 °C or 40 hours darkness at 28 °C.

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Yao-Chien Chang and William B. Miller

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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Yao-Chien Chang and William B. Miller

Upper leaf necrosis (ULN) on Lilium `Star Gazer' has been shown to be a calcium (Ca) deficiency disorder. Initial symptoms of ULN tend to appear on leaf margins. Before flower buds are visible, young expanding leaves are congested and overlap each other on the margin. In the current study, we examined the relationship between leaf enclosure, transpiration, and upper leaf necrosis. We demonstrated that low transpiration rate and enclosure of young leaves played an important role in the occurrence of ULN. Young expanding leaves are low transpiration organs. The younger the leaf, the lower the transpiration rate and Ca concentration. Leaf enclosure further reduced transpiration of these young leaves and promoted ULN. Upper leaf necrosis was suppressed by manually unfolding the leaves using a technique we refer to as artificial leaf unfolding (ALU). ALU minimized leaf congestion, exposing leaves that were previously enclosed. We demonstrated that the effect of ALU was not the consequence of thigmomorphogenesis, as ULN was not reduced by mechanical perturbation in lieu of ALU. With ALU, transpiration of upper leaves was significantly increased and Ca concentration of the first leaf immediately below the flower buds was increased from 0.05% to 0.20%. We concluded that leaf enclosure promoted ULN occurrence, and ALU suppressed ULN primarily by increasing transpiration. The use of overhead fans to increase airflow over the tops of the plants significantly reduced both ULN incidence and severity.

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Yao-Chien Chang and William B. Miller

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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Joseph P. Albano and William B. Miller

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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Anil P. Ranwala and William B. Miller

Experiments were conducted to evaluate storage temperature, storage irradiance and prestorage foliar sprays of gibberellin, cytokinin or both on postharvest quality of Oriental hybrid lilies (Lilium sp. `Stargazer'). Cold storage of puffy bud stage plants at 4, 7, or 10 °C in dark for 2 weeks induced leaf chlorosis within 4 days in a simulated consumer environment, and resulted in 60% leaf chlorosis and 40% leaf abscission by 20 days. Cold storage also reduced the duration to flower bud opening (days from the end of cold storage till the last flower bud opened), inflorescence and flower longevity, and increased flower bud abortion. Storage at 1 °C resulted in severe leaf injury and 100% bud abortion. Providing light up to 40 μmol·m-2·s-1 during cold storage at 4 °C significantly delayed leaf chlorosis and abscission and increased the duration of flower bud opening, inflorescence and flower longevity, and reduced bud abortion. Application of hormone sprays before cold storage affected leaf and flower quality. ProVide (100 mg·L-1 GA4+7) and Promalin (100 mg·L-1 each GA4+7 and benzyladenine (BA)) effectively prevented leaf chlorosis and abscission at 4 °C while ProGibb (100 mg·L-1 GA3) and ABG-3062 (100 mg·L-1 BA) did not. Accel (10 mg·L-1 GA4+7 and 100 mg·L-1 BA) showed intermediate effects on leaf chlorosis. Flower longevity was increased and bud abortion was prevented by all hormone formulations except ProGibb. The combination of light (40 μmol·m-2·s-1) and Promalin (100 mg·L-1 each GA4+7 and BA) completely prevented cold storage induced leaf chlorosis and abscission.

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Susan E. Trusty and William B. Miller

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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Chad T. Miller, Neil S. Mattson, and William B. Miller

Oxalis regnellii, the shamrock plant, and O. triangularis are niche ornamental greenhouse crops produced and marketed primarily for their foliage; thus, it is imperative to produce the fullest, most colorful, and blemish-free plants as possible. An experiment was conducted using O. regnellii, comparing two irrigation methods, overhead (drip) irrigation versus subirrigation, in addition to varying 20N–2.2P–16.6K fertilizer concentrations, 50, 100, 200, 300, and 500 mg·L−1 nitrogen (N). Overhead irrigation produced larger plants with increased root mass as compared with subirrigation. Low or high fertilizer concentration (50 mg·L−1 N and 500 mg·L−1 N, respectively) led to reductions in the fresh and dry weight of overhead-irrigated plants compared with intermediate fertilizer rates. At the highest fertilizer treatment, plant height was decreased. Chlorophyll index (based on SPAD readings) increased linearly and quadratically for subirrigated and overhead-irrigated plants, respectively. A second study analyzed the effects of seven different fertilizer formulations on growth of O. regnellii and O. triangularis. The fertilizers used in this study were Jack's LX All Purpose (21N–2.2P–16.6K), Peter's Professional (20N–8.8P–16.6K), Jacks Poinsettia FeED Ca-Mg (15N–1.7P–12.5K), Jack's Petunia FeED Mg (20N–1.3P–15.7K), Peter's Professional Peat-Lite Dark Weather Feed (15N–0P–12.5K), Peter's Excel Cal-Mag (15N–2.2P–12.5K), and the slow-release fertilizer Osmocote® (14N–4.2P–11.6K). Growth of both species was significantly reduced by fertilizers that contained little or no phosphorus (P). Current water-soluble fertilizer recommendations of 21N–2.2P–16.6K or slow-release granule fertilizer of 14N–4.2P–11.6K (Osmocote®) produced acceptable, marketable plants, whereas the best O. regnellii and O. triangularis plants were produced using 15N–2.2P–12.5K and 20N–1.3P–15.7K formulations, likely as a result of the additional calcium (Ca), magnesium (Mg), and iron (Fe) in the mixtures.

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Christopher B. Cerveny, William B. Miller, and Alan G. Taylor

Ranunculus asiaticus (L.) is an ornamental geophyte with some commercial production challenges presumed to be related to the storage of its desiccation tolerant tuberous roots (TRs). We investigated the influence of temperature and relative humidity during storage on viability of R. asiaticus TRs. The TRs were stored in specialized chambers for controlling relative humidity under flow-through or closed systems. In the flow-through system, air was bubbled through glycerol–water solutions to create relative humidities of 20%, 40%, 60%, 80%, or 100% and then passed through storage chambers held at 5, 20, or 35 °C for up to 20 weeks. In closed storage, tissue was equilibrated to a given moisture content (fresh basis) at 15 °C by suspending TRs over glycerol–water solutions (35%, 60%, or 85% relative humidity) with fans to circulate air. These containers were closed for 4 weeks and then tissue was transferred to sealed jars for up to 17 weeks at 5 or 25 °C. In both systems, TRs held with elevated temperature and relative humidity had the largest decrease in percent survival when planted after storage. Flow-through storage gave greater variability in TRs moisture content than closed storage. Tuberous roots at 25 °C had higher respiration rates than at 5 °C under closed storage; elevated moisture content also led to increased respiration. From these results it can be concluded that R. asiaticus dry TRs should be stored cool and dry for long-term viability.

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Susan S. Liou, Chris B. Watkins, and William B. Miller

During transport and the subsequent storage of tulip bulbs, inadvertent failure in ventilation and/or high contamination of Fusarium-infected bulbs may expose healthy bulbs to high concentrations of ethylene. Ethylene is known to cause many detrimental effects on forcing quality, including gummosis, increased respiration, flower bud abortion, bulb splitting and poor rooting. In this work, exposure duration and timing as well as the post-stress storage temperatures were evaluated for their potential effects on ethylene sensitivity in bulbs of four tulip cultivars. Degree of damage in sensitive cultivars `Apeldoorn' and `World's Favourite' increased with days at about 10 ppm ethylene starting at 9 and 16 days respectively. This effect strongly depended on timing of ethylene stress, as late treated bulbs showed more severe responses to ethylene treatment than early treated bulbs. Additionally, bulbs that were cooled immediately after ethylene stress, compared with those stored at 17 °C after stress, have significantly higher flowering quality in all attributes measured. This response was also strongly dependent on timing of ethylene stress and cultivar. Implications of the potential cold reversal of ethylene damage as well as effects of ethylene exposure duration and timing of stress on shipping and storage recommendations will be discussed.