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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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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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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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Joseph P. Albano and William B. Miller

Marigolds under iron deficiency stress exhibited characteristics associated with iron efficiency (e.g. induced reductase and rhizosphere acidification). Ferric reduction rates for roots of the minus Fe-DTPA treatment group was 0.97 μmol·g FW-1·h-1, 14 times greater than the 17.9 μM Fe-DTPA treatment group. Excised primary lateral roots from the minus Fe-DTPA and 17.9 μM Fe-DTPA treatment groups embedded in an Fe reductase activity gel visually confirmed an increased Fe reduction rate for the minus Fe-DTPA treatment group. The pH of the nutrient solution one week after initiation of treatments indicated that the minus Fe-DTPA treatment group was 1 pH unit lower than the 17.9 μM Fe-DTPA treatment group at 4.1 and 5.1, respectively.

Free access

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.

Open access

William B. Miller, Wanxiang Lu, and Dongqin Tang

Although ethephon is commonly used as a plant growth regulator during commercial production of horticultural crops, information on its movement within plants is limited. In this study, we developed a method to detect ethephon in plant tissues, and determined ethephon localization and movement using tomato (Solanum lycopersicum L.) as a model system. Tissues were ground in an acidic buffer that preserved ethephon intact. Ethylene was released from the extracts by adding sodium hydroxide and was determined subsequently by gas chromatography. Ethephon was detected in leaves within 1 hour of application to peat-based root zones and within 10 minutes in hydroponics. In a pulse–chase experiment, ethephon levels increased initially, then decreased after the plants were returned to ethephon-free solutions. Ethephon was present in directly collected xylem fluid; fluid collected from petiole stumps (after leaf blade excision) had similar ethephon levels between the different petioles. Stem girdling had no effect on ethephon accumulation in leaves. Together, these data indicate ethephon is readily mobile in the xylem stream and provides insight into the commercial use of ethephon as a root zone-applied growth regulator.

Free access

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.

Open access

Douglas A. Bailey and William B. Miller

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).

Free access

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.

Free access

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.