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

A broccoli (Brassica oleracea var. botrytis L.) seedling bioassay was used to measure paclobutrazol activity and distribution in two growing media following drench or subirrigation applications. The bioassay exhibited a saturation-type response curve for paclobutrazol concentrations up to 1000 μg·L-1 in solution and 100 μg·L-1 in the media. The concentration of paclobutrazol required to achieve one-half of the maximum observed bioassay activity was 3-fold as high in bark-based commercial potting medium as in a peat-based medium. Less than 2% of applied paclobutrazol leached out during the drench application despite the collection of up to 50 mL of leachate per 120 mL of the solution (1000 μg·L-1) that was applied per 15-cm pot. Immediately following drench application, paclobutrazol concentrations in both media were highest in the uppermost 2.5 cm and decreased downward. By 3 weeks after treatment, drench-applied paclobutrazol had moved into lower depths. Distribution of paclobutrazol was limited to the bottom 2.5 cm of media when applied as a subirrigation soak. Chemical name used: (±)-(R*,R*)-β-[(4-chlorophenyl)methyl]-α-(1,1-dimethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol).

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Ria T. Leonard, Terril A. Nell, Lars Hoyer, Jim E. Barrett, and David G. Clark

Postproduction evaluation trials have been developed in North America and Europe to test postproduction performance of potted roses from individual growers. The results of the trials have been compiled on the “Roses On The Web” Website (www.parade.dk). Roses on the WEB is a cooperative project between Poulsen Roses ApS, Denmark, the Danish Institute of Agricultural Sciences, and the Univ. of Florida. The goal of the Website is to provide growers participating in the evaluation trials a quick and easy way to obtain results on the postproduction quality of their roses. Plants receive 4 days of simulated transport, sleeved in a box in darkness at 16 °C. After transport, plants are maintained at 20 °C at 8 μmol·m–2·s–1 for 12 hours/daily. Relative humidity is maintained at 55% ± 5%. To determine quality, several parameters are recorded at day 0 (day of arrival), 11, 18, 22, and 28. The recordings include the number of open and damaged flowers and buds, percentage of damaged leaves, and the presence of disease and pests. Based on the results of all the measurements, each plant is given a postproduction rating or index, indicating quality. Results from each trial are tabulated and stored on the Website. Growers are able to view their results by entering a password. Growers can evaluate their quality over time and are also able to compare their quality with other growers. Many quality problems are manifested in the postproduction environment and can often be directly related to incorrect greenhouse conditions and/or cultural practices. “Roses On The Web” is a tool that provides quick, up-to-date information that can be crucial to the success of a grower. Differences in quality were found based on grower, time of year and variety.

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David G. Clark, Christopher Dervinis, James E. Barrett, and Terril A. Nell

Experiments were conducted to determine if the seedling hypocotyl elongation and petal abscission assays could be used to identify differences in ethylene sensitivity among seedling geranium (Pelargonium ×hortorum) cultivars. When seedlings of six geranium cultivars were germinated and grown in the dark in the presence of the ethylene biosynthetic precursor 1-aminocyclopropane-1-carboxylic acid (ACC) at various concentrations, they exhibited the triple response (measured as reduced hypocotyl length). While seedlings from all six cultivars were sensitive to ACC, `Scarlet Elite' seedlings were most sensitive, and `Multibloom Lavender', `Elite White' and `Ringo 2000 Salmon' seedlings were the least sensitive when germinated and grown on 20 mm [2022 mg·L-1 (ppm)] ACC. Florets representing three developmental stages of each of the six cultivars were exposed to 1 μL·L-1 of exogenous ethylene for 0, 30, or 60 min to determine if differences in cultivar sensitivity could be determined for petal abscission. Of the six cultivars tested, `Ringo 2000 Salmon', `Multibloom Lavender' and `Elite White' were the least ethylene sensitive. Florets were also self-pollinated to test for cultivar differences in ethylene synthesis and subsequent petal abscission. Ethylene production and petal abscission were both promoted in self-pollinated florets compared to nonpollinated florets. `Ringo 2000 Salmon', `Multibloom Lavender' and `Elite White' florets produced similar amounts of ethylene as all other cultivars, but abscised fewer petals after pollination. Our results indicate that the seedling hypocotyls elongation assay may be used to identify geranium cultivars with reduced sensitivity to ethylene. The data also suggest that genetic variability exists among geraniums for both ethylene sensitivity and biosynthesis.

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Erika K. Gubrium, Donna J. Clevenger, David G. Clark, James E. Barrett, and Terril A. Nell

A series of experiments on ethylene-insensitive (EI) petunia plants (Petunia ×hybrida Hort. Vilm.-Andr.) generated in two genetic backgrounds were conducted to determine the involvement of ethylene in horticultural performance. Experiments examined various aspects of horticultural performance: days to flower, flower senescence after pollination and without pollination, fruit set and ripening, and adventitious root formation on vegetative stem cuttings. The development of EI plants was altered in several ways. Time from seed sowing to first flower anthesis was decreased by a week for EI plants grown at 26/21 °C. Flower senescence in nonpollinated and self-pollinated flowers was delayed in all EI plants compared to wild-type plants. Fruit set percentage on EI plants was slightly lower than on wild-type plants and fruit ripening on EI plants was delayed by up to 7 days. EI plants produced fewer commercially acceptable rooted cuttings than wild-type plants. There was a basic difference in the horticultural performance of the two EI lines examined due to a difference in the genetic backgrounds used to generate the lines. EI plants displayed better horticultural performance when grown with day/night temperatures of 26/21 °C than 30/24 °C. These results suggest that tissue-specific ethylene insensitivity as well as careful consideration of the genetic background used in transformation procedures and growth conditions of etr1-1 plants will be required to produce commercially viable transgenic floriculture crops. EI petunias provide an ideal model system for studying the role of ethylene in regulating various aspects of plant reproduction.

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Wilfredo Colón-Guasp, Terril A. Nell, Michael E. Kane, and James E. Barrett

The use of abscisic acid (ABA) as an in vitro prehardening treatment to enhance ex vitro acclimatization of Stage III Aronia arbutifolia plantlets was explored. Effects of ABA (0-4 mg·liter-1) pretreatment on ex vitro shoot growth, leaf carbon assimilation (LCA) and nonstructural carbohydrate content were evaluated during plantlet acclimatization under two photosynthetic photon flux (PPF) levels (450 and 650 μmol·m-2·s-1). Stage III plantlets rooted in the presence of ABA exhibited both shoot growth inhibition and transient negative LCA rates at time of transfer ex vitro. Regardless of treatment, maximum LCA rates were achieved by day 20 post-transplant. Pretreatment with ABA had no effect on stem or leaf starch content at time of transplant, however, leaf and stem soluble sugar content was higher in ABA treated plantlets than controls. Further suppression of shoot growth and alteration in the pattern of stem starch utilization occurred at the higher irradiance level. These results indicate that ABA pretreatments provide no physiological advantage that would facilitate ex vitro acclimatization of Aronia plantlets.

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G.H. Pemberton, Terril A. Nell, Ria T. Leonard, A.A. De Hertogh, Lena Gallitano, and James E. Barrett

Forced `Bumalda' and `Etna' Astilbe were evaluated for postproduction quality and longevity. Plants were sleeved, boxed and held at 9±2C for 3 days to simulate shipping at the following stages of floral development: tight bud (TB), 1-3 florets open, 25% florets open, 50% florets open, and 75% florets open. They were then placed at 21C and 14 μmol·m-2·s-1 (12h daylength) until flower senescence. Percent of inflorescences flowering increased from 34% at TB stage to 94% when shipped with 25 % of the florets open. `Etna' longevity increased from 3 days at TB stage to 12 days at 25% open stage. Optimum quality and longevity occurred when ≥ 25% of the florets were opened at shipping.

In a second experiment, `Bumalda' and `Etna' Astilbe were held at 18, 21 and 24C at irradiance levels of 7 or 14 μmol·m-2·s-1 when 25% of the florets were open. At 18C, longevity increased under 14 μmol·m-2·s-1 from 14 to 17 days. At 24C, longevity was only 10 days for both irradiance levels.