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

The postharvest longevity of fresh-cut flowers is often limited by the accumulation of bacteria in vase water and flower stems. Aqueous chlorine dioxide is a strong biocide with potential application for sanitizing cut flower solutions. We evaluated the potential of chlorine dioxide to prevent the build-up of bacteria in vase water and extend the longevity of cut Matthiola incana `Ruby Red', Gypsophila paniculata `Crystal' and Gerbera jamesonii `Monarch' flowers. Fresh-cut flower stems were placed into sterile vases containing deionized water and either 0.0 or 2 μL·L–1 chlorine dioxide. Flower vase life was then judged at 21 ± 0.5 °C and 40% to 60% relative humidity. Inclusion of 2 μL·L–1 chlorine dioxide in vase water extended the longevity of Matthiola, Gypsophila and Gerbera flowers by 2.2, 3.5, and 3.4 days, respectively, relative to control flowers (i.e., 0 μL·L–1). Treatment with 2 μL·L–1 chlorine dioxide reduced the build-up of aerobic bacteria in vase water for 6 to 9 days of vase life. For example, addition of 2 μL·L–1 chlorine dioxide to Gerbera vase water reduced the number of bacteria that grew by 2.4- to 2.8-fold, as compared to control flower water. These results confirm the practical value of chlorine dioxide treatments to reduce the accumulation of bacteria in vase water and extend the display life of cut flowers.

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

The vase life of many cut flowers is often limited by bacterial occlusion of stem bases. In this study, we tested the efficacy of a novel antimicrobial agent, aqueous chlorine dioxide (ClO2), to extend the longevity of cut Gerbera flowers by reducing the number of bacteria in vase water. Commercially mature and freshly cut Gerbera jamesonii `Monarck' flowers were placed into clean vases containing deionized water and 0, 2, 5, 10, 20, and 50 μL·L-1 ClO2. Stems were then maintained in solutions at 21 ± 0.5 °C and 42 ± 11% relative humidity until the end of vase life. Inclusion of 2, 5, and 10 μL·L-1 ClO2 in vase water had beneficial effects on flower longevity. For instance, treatment with 5 and 10 μL·L-1 ClO2 extended flower longevity by 1.4-fold or 3.7 days, as compared to control flowers (0 μL·L-1 ClO2). In contrast, exposure to the higher concentrations of 20 and 50 μL·L-1 ClO2 did not extend flower vase life. Relative to control flowers, treatment with 10 μL·L-1 ClO2 delayed the onset of detectable bacterial colonization of vase solutions from day 3 to day 6 of vase life. However, this ClO2 treatment did not reduce the number of bacteria that subsequently accumulated in vase water as compared to control flowers. Treatment with 10 μL·L-1 ClO2 also increased rates of solution uptake by stems and reduced the loss of flower fresh weight over time. These results highlight the potential use of ClO2 treatments to extend the postharvest longevity of Gerbera flowers.

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

Exposure to 0.1, 1.0, or 10 μL·L−1 ethylene for 4 days at 21 °C reduced the display life of 17 commonly traded potted foliage plant genotypes (Aglaonema ‘Mary Ann’, Anthurium scherzerianum ‘Red Hot’ and ‘White Gemini’, Aphelandra squarrosa ‘Dania’, Chlorophytum comosum ‘Hawaiian’, Codiaeum variegatum pictum ‘Petra’, Dieffenbachia maculata ‘Carina’, Dracaena marginata ‘Bicolor’ and ‘Magenta’, Euphorbia milii ‘Gaia’, Euphorbia splendens ‘Short and Sweet’, Ficus benjamina, Polyscias fruticosa ‘Castor’, Radermachera sinica ‘China Doll’, Schefflera elegantissima ‘Gemini’, Schefflera arboricola ‘Gold Capella’, Spathiphyllum ‘Ty's Pride’). Ethylene treatment hastened leaf and bract abscission or senescence. The responsiveness of plants to ethylene varied considerably; six genotypes were sensitive to 0.1 μL·L−1 ethylene, whereas three genotypes required exposure to 10 μL·L−1 ethylene to trigger visible injury. Four genotypes (Asplenium nidus, Chamaedorea elegans ‘Neathe Bella’, Hedera helix ‘Chicago’, Syngonium podophyllum ‘White Butterfly’) included in our study were insensitive to ethylene. Treating Aglaonema ‘Mary Ann’, Polyscias fruticosa ‘Castor’, and Schefflera arboricola ‘Gold Capella’ plants with 0.9 μL·L−1 1-methylcyclopropene (1-MCP, provided as EthylBloc™), a gaseous ethylene-binding inhibitor, for 4 to 5 h at 21 °C reduced the deleterious effects of ethylene. The release of 1-MCP from two sachets containing EthylBloc™ into a single shipping box also protected Aphelandra squarrosa ‘Dania’, Euphorbia milii ‘Gaia’, Polyscias fruticosa ‘Elegans’, and Schefflera arboricola ‘Gold Capella’ plants from ethylene injury after simulated transport. Our data reveal the genetic variation in ethylene sensitivity among potted foliage plants and highlight genotypes that benefit from 1-MCP treatment.

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Andrew J. Macnish, David H. Simons, Daryl C. Joyce, John D. Faragher and Peter J. Hofman

Postharvest longevity of some cut flowers is shortened by exposure to ethylene gas. Adverse effects of ethylene may be prevented by treatment with 1-methylcyclopropene (1-MCP) gas. Responses of 14 different native Australian cut flowers to 1-MCP and ethylene applied at concentrations of 10 nL·L-1 and 10 μL·L-1, respectively, were examined. Each gas was applied alone for 12 hours at 20 °C and they were also applied in series. Vase lives of Ceratopetalum gummiferum, Chamelaucium uncinatum, Grevillea `Kay Williams' and `Misty Pink', Leptospermum petersonii, Telopea `Shady Lady', and Verticordia nitens were reduced by ethylene treatment. Treatment with 1-MCP generally protected these cut flowers against subsequent exposure to ethylene. The 1-MCP treatment usually did not extend their vase lives in the absence of exogenous ethylene.

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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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Andrew J. Macnish, Malkeet S. Padda, Francine Pupin, Pavlos I. Tsouvaltzis, Angelos I. Deltsidis, Charles A. Sims, Jeffrey K. Brecht and Elizabeth J. Mitcham

The efficacy of several proprietary plastic pallet cover systems to maintain strawberry (Fragaria ×ananassa) fruit quality during commercial shipment was determined. ‘Albion’ fruit were harvested from farms near Watsonville, CA. Fruit in vented plastic clamshells were palletized and forced-air cooled to 33–35 °F. Different cover systems (CO2 West, PEAKfresh, PrimePro, Tectrol) were placed over the pallets. Pads that released carbon dioxide (CO2) gas were placed inside the CO2 West cover. The Tectrol cover was sealed to the pallet base, a partial vacuum was applied, and pressurized CO2 gas was injected inside. The systems other than Tectrol remained open at the base. Six separate shipments of palletized fruit were transported in refrigerated (32–39 °F) truck trailers to distribution centers in either Florida or Georgia in 2.3–4.7 days. CO2 concentrations within pallets at the beginning and end of transport were highest (11% to 16%) in the sealed Tectrol system and relatively low (0.06% to 0.30%) in the open CO2 West, PEAKfresh, and PrimePro cover systems. Relative to noncovered control fruit, which lost 0.8% fresh weight during shipment, the pallet covers reduced the transport-related weight loss by 38% to 52%. The incidence of fruit decay was low (1.0% to 1.4%) after transport but increased substantially following a 2-day shelf life at 68 °F. However, fruit from the Tectrol pallets exhibited significantly less decay (36%) after shelf life than the CO2 West (39%), noncovered control (41%), PrimePro (42%), and PEAKfresh (43%) pallets. Fruit sensory quality was unaffected by the different pallet cover systems. Our findings show that transporting strawberries in the sealed Tectrol pallet cover system, in which CO2 concentrations were elevated to 11% to 16%, was most effective in complementing current low temperature management practices to maintain fruit quality.