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William M. Womack, Terril A. Nell, and James E. Barrett

Dormant-budded `Prize' azaleas (Rhododendron sp.) were held at 2C, 7C, 13C, or 18C for 1, 2, 4, 6, 8, or 10 weeks then forced in walk-in growth chambers (29C day/24C night). Holding at 2C delayed flowering by 5-7 days over 7C and 13C. Plants held at 2C, 7C, or 13C for at least 4 weeks had approximately 50% buds showing color at marketability (8 open flowers). Plants held at 18C never exceeded 35% buds showing color at marketability. Increase in buds showing color was not apparent for plants were held at 7C, 13C, or 18C for more than 6 weeks; however, holding at 2C resulted in increasing percentages of buds showing color for holding periods longer than 6 weeks. Plants chilled at 13C and 18C showed significant increases in bud abortion after 8 or 10 weeks of cooling with most plants never reaching marketability (8 open flowers). These plants also had an increased proliferation of bypass shoots during cooling and forcing over other treatments.

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Thea M Edwards, Terril A. Nell, and James E. Barrett

Increased rates of senescence and ethylene related damage of potted flowering plants have been observed in supermarket produce areas where flowers and climacteric produce are displayed together. Ethylene levels in produce areas were found to average 20 ppb. An open system of clear glass chambers with fiberglass lids was designed to simulate retail supermarket conditions. The chambers were kept in postharvest rooms where light level and temperature could be controlled. In a 3 by 3 by 3 Box-Behnken design, Sunblaze `Candy' miniature potted roses were exposed to three levels of ethylene, 20, 40, and 80 ppb, for 1, 2, and 4 days. The three light levels used were: 0, 7, and 14 μmol·m-2·s-1. Ethylene damage was based on leaf and bud drop and decreased flower longevity.

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Trinidad Reyes, Terril A. Nell, and James E. Barrett

`Tara' and `Boaldi' were fertilized with 150 and 450 ppm from 20N–4.7P–16.6K soluble fertilizer and moved at flowering to postproduction conditions (21 ± 2C and 10 μmol·m–2·s–1). Shipping was simulated for 1 week at 26C. `Tara' exhibited burned leaf margins (necrosis) and chlorosis following shipping. At 150 ppm, leaves had brown, dried margins, but the damage did not progress indoors. Necrosis was worse at 450 ppm. Leaf chlorosis/necrosis of non-shipped plants at the 450 fertilizer level did not appear until the 3rd week indoors. At experiment termination, no leaf damage occurred in non-shipped `Tara' or `Boaldi' with 150 ppm. `Boaldi' did not show damage after shipping regardless of the treatment but symptoms (necrosis and wilting of leaves) evolved during the first 2 weeks indoors on plants fertilized with 450 ppm. A 50% reduction in root soluble carbohydrates was found at the highest fertilizer rate at flowering, suggesting that leaf chlorosis/necrosis is related to carbohydrate depletion in chrysanthemum.

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Brent M. Chapman, James E. Barrett, and Terril A. Nell

Catharanthus roseus `Cooler Peppermint' were grown under four different watering regimes [well-watered (WW), wilt plus 1 day (W+1), wilt plus 3 days (W+3), and wilt plus 1 day during the last 2 weeks only (L W+1)] and two different light levels [1100 and 750 μmol·m–2·s–1]. Stress treatments affected finished plant size and leaf area as well as stomatal conductance, water potential and time to wilt during two dry-down periods imposed at the end of an 8-week production cycle. W+3 plants were 50% smaller with 50% less leaf area compared to WW plants. During the second dry-down period, WW plants in high light wilted in 2 days vs 4 days for the W+3 plants. Similarly, WW plants in low light wilted in 3 days vs 6 days for the W+3 plants. The W+3 plants maintained significantly higher water potentials and greater stomatal conductances than the other treatments throughout both dry-down periods.

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Jeff B. Million, James E. Barrett, and Terril A. Nell

Drench applications of paclobutrazol (PBZ) are becoming increasingly popular as a means for controlling height in potted plants, and research is being conducted to quantify the distribution of PBZ following applications. In one trial, 120 ml of 0 or 1 mg 1-1 PBZ were applied to 15-cm pots filled with either Vergro Klay Mix (no bark) or Metro Mix 500 (bark). A bioassay using broccoli (Brassica oleracea L. Italica) seedlings was used to quantify PBZ in leachates and media following treatment drenches. Leachate PBZ concentrations were lower for Vergro than for Metro Mix 500; however, leachates for both media were <0.1 mg·liter–1. Concentrations of PBZ in media decreased with depth and were four to 10 times higher in the uppermost 2.5 cm than in lower horizons. For the uppermost 2.5 cm of media, higher PBZ concentrations were recovered in Metro Mix 500 than in Vergro. A follow-up study will compare surface vs. subsurface application methods on the movement of PBZ into pots.

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Nadia Roude, Terril A. Nell, and James E. Barrett

Plant height, flower diameter, days to flower, and longevity of `Iridon' chrysanthemums [Dendranthemum × grandiflorum (Ramat.) Kitamura] were not affected by various N and K concentrations (112, 225, 337, and 450 mg·liter-1) supplied during the last 5 weeks of production. However, increasing N concentration increased medium conductance, while varying K concentration had no effect on conductance. Visual grade of `Iridon' after 3 weeks in a simulated interior environment showed an interaction between concentrations of N and K. In a second study, growth and longevity of `Iridon' were affected by NH4: NO3 ratios. Plants receiving a 0:1.0 ratio flowered 4 days later than plants receiving a 0.5:0.5 ratio and were taller than plants fertilized with a 1.0:0 ratio. Longevity was greater in plants receiving a 0:1.0 ratio than in those receiving 0.5:0.5 or 0.75:0.25 ratios. Also, longevity was similar in plants receiving NH4: NO3 ratios of 0:1.0, 0.1:0.9, 0.2:0.8, and 0.3:0.7. Plants receiving 0:1.0 lasted 6 days longer than those receiving a 0.4:0.6 ratio.

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Richard K. Schoellhorn, James E. Barrett, and Terril A. Nell

`Improved Mefo' chrysanthemums were grown at 22C/18C and 34C/28C day/night temperature regimes to evaluate the failure of lateral bud development following pinching of this temperature sensitive cultivar. The number of viable buds on plants at the high temperatures was 40% of number at low temperature. Loss of bud viability was categorized as those buds that were: 1) absent, or 2) those in which growth was present, but inhibited. Inhibited buds were visible swellings surrounded by dense masses of secondary cell wall material. Anatomical studies were completed to verify the absence of lateral buds and determine what cellular changes imposed inhibition on those buds that did develop. A second group of experiments demonstrated that moving low-temperature plants to the high temperature caused production of viable buds to decline. Plants were moved from high temperatures to low, and reciprocally to high from low temperature. Anatomical sampling of apical meristems began at time of shift and at 1, 2, 4, and 8 days after temperature shift. High-temperature meristems possessed predominantly non-viable lateral buds, with few viable buds present.

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Terril A. Nell, Ria T. Leonard, and James E. Barrett

Production irradiance levels on growth, light compensation point (LCP), dark respiration (DR), and interior longevity of potted chrysanthemum (Demfranthema grandiflora Tzvelev. cvs. Iridon and Mountain Peak) and poinsettia (Euphorbia pulcherrima Wind. cvs. Annette Hegg Dark Red and Gutbier V-10 Amy) were determined. LCP and DR were measured at anthesis and during acclimatization to interior conditions (10 μmol·s-1·m-2). Days to flowering, inflorescence diameter, total chlorophyll, and interior longevity of chrysanthemum increased when maintained at a mean maximum photosynthetic photon flux density (PPFD) of 500 μmol·s-1·m-2 compared to plants shifted to 300 or 100 μmol·s-1·m-2 8 weeks after planting. LCP and DR were highest at anthesis and were reduced 38% and 49%, respectively, for chrysanthemum and 19% and 42%, respectively, for poinsettia within 3 days in interior conditions. Chrysanthemum plants shifted to 300 μmol·s1·m-2 during production had lower LCP and DR rates at anthesis and throughout time in interior conditions compared to plants maintained at 500 μmol·s-1·m-2. The acclimatization of chrysanthemum to reduced production PPFD is of little significance because interior longevity is reduced. No differences were found in the LCP or DR of poinsettia or chrysanthemum cultivars that differ in interior performance, demonstrating that these physiological characteristics are not good indicators of interior longevity for chrysanthemum and poinsettia.

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G.H. Pemberton, Terril A. Nell, and James E. Barrett

Senescence of gladiolus flowers, like many geophytes, does not involve a climacteric burst of ethylene. Eleven gladiolus cultivars were screened and all were non-climacteric (NC) for both respiration and ethylene production. Average ethylene levels for individual flowers were 0.5 μl C2H4/kg per h or less. As in other NC flowers, protein synthesis may be linked to senescence. Our goal was to identify specific proteins that were involved in the senescence process that could be used as indicators of postharvest longevity. SDS-PAGE protein profiles of cut gladiolus flowers were determined from a tight bud stage to senescence. Both increases and decreases were observed in major polypeptides that may be connected to postharvest flower longevity. Total protein content of gladiolus flower petals decreased by ≈70% during the profile period. This could explain the relatively short postharvest life of 3 to 5 days for individual gladiolus flowers. Total protein profiles were probed with an ACC synthase antibody to establish the relationship of this enzyme in NC senescence.

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Michelle H. Williams, Terril A. Nell, and James E. Barrett

It is generally accepted that ethylene production is centrally located in petal senescence, however, non-climacteric flowers senesce irrespective of the presence of ethylene. The regulation of flower senescence may well be linked to protein synthesis. Our objective was to develop a simple tool which can be used in breeding programmes and\or the market place to determine potential longevity of a flower. Here, SDS-PAGE protein profiles of both potted and cut chrysanthemum flowers were determined from flowering to senescence. Generally, only minor changes in both protein content and the proportion of the major polypeptides were observed in the potted flowers. However, polypeptides at 40, 45 and 65 kDa increased during flower senescence and are of particular interest because they could be linked to flower longevity. The apparent stability of the proteins may contribute to the long postharvest life of the potted chrysanthemum.