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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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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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Christopher Ramcharan, Dewayne L. Ingram, Terril A. Nell, and James E. Barrett

Short-term effects of root-zone temperatures (RZT) of 28, 33, 38, and 43C for 6 hours daily on container-grown Musa spp. (AAA) `Grande Naine' and Ixora chinensis L. `Maui' were determined under greenhouse and growth room conditions. Diurnal fluctuation of leaf carbon assimilation (LCA) was altered by treatments. In the growth room at 43C, the maximum LCA occurred about midday for banana, but not until afternoon in ixora. LCA was highest (0.53 mg CO2/m2 per sec) in banana with a 33C RZT under greenhouse conditions, while it was equally high (0.74 mg CO2/m2 per sec) at 33 and 38C in a growth room. In ixora, 33C induced the highest LCA (0.40 mg CO2/m2 per sec) in the greenhouse at 1200 hr, but there were no apparent differences in midday LCA between plants with RZT of 28, 33, and 38C in the growth room. Effects of RZT and environment on the daily fluctuations of gaseous exchange processes raise questions about using measurements at only one time during the day to separate treatment effects.

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Ayumi Suzuki, Ria T. Leonard, Terril A. Nell, Jim E. Barrett, and David G. Clark

It has traditionally been recommended to cut flower stems underwater to reduce blockage and improve water uptake, although little scientific information relates this practice to vase life. The purpose of our study was to evaluate the benefit of this processing technique on quality and longevity of several cut flowers species. Stems were either cut dry or cut wet under deionized water with a stainless steel blade and placed into vases containing a commercial floral preservative. Water samples were obtained from the cutting tank over time during stem processing for bacteria counts. Stems were maintained at 2 °C at 10 μmol·m–2·s–1 (12 h/day). The results were variable from shipment to shipment, possibly due to differences in stem quality or cutting water quality. In most cases, cutting underwater had no effect on longevity of alstroemeria, chrysanthemums, gerbera daisy, roses, or snapdragons. However, in a few instances, cutting underwater improved longevity slightly. Cutting stems underwater was consistently effective in increasing longevity 2-4 days for carnations. Bacteria counts in the cutting tank water after 500 stems were processed were 6/34 × 106 propagules/mL and increased to 1.00 × 107 propagules/mL after 1000 stems. The increase in bacteria decreased leaf quality in roses and reduced the number of snapdragon flowers that opened, but did not affect longevity. In gerberas, however, longevity decreased 2 days. A high concentration of bacteria in the cutting water may effect quality and longevity of many cut flower species and may negate any benefit in cutting stems underwater.

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Andrew J. Macnish, Ria T. Leonard, Ana Maria Borda, and Terril A. Nell

Natural variation in the postharvest quality and longevity of ornamental plants can often be related to differences in their response to ethylene. In the present study, we determined the postharvest performance and ethylene sensitivity of cut flowers from 38 cultivated Hybrid Tea rose genotypes. The vase life of the cultivars varied considerably from 4.5 to 18.8 days at 21 °C. There was also substantial variation in the degree of flower opening among genotypes. Exposure to 1 μL·L−1 ethylene for 24 h at 21 °C reduced the longevity of 27 cultivars by 0.8 to 8.4 days (18% to 47%) by accelerating petal wilting and abscission. Ethylene treatment also significantly reduced rates of flower opening in 17 sensitive cultivars and in six cultivars that showed no ethylene-related reduction in vase life. Five cultivars showed no reduction in vase life or flower opening in response to ethylene exposure. Pre-treating stems with 0.2 mm silver thiosulfate liquid or 0.9 μL·L−1 1-methylcyclopropene (1-MCP) gas for 16 h at 2 °C reduced the deleterious effects of ethylene. The release of 1-MCP from two sachets containing EthylBloc™ into individual shipping boxes also protected flowers against ethylene applied immediately after a 6-d commercial shipment. The duration of protection afforded by the 1-MCP sachet treatment was greatest when flowers were maintained at low temperature.

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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.