Ornamental plant producers use cuttings shipped from around the world for finished plant production. The value of unrooted cutting imports into the United States totaled ≈$61 million in 2006 with the bulk coming from Central America, South America, Mexico, and Asia (Foreign Agricultural Service, 2007). In the top 15 floricultural crop-producing states, flats, hanging baskets, and pots of geraniums (Pelargonium L'Hér. ex Ait.), poinsettias (Euphorbia pulcherrima Willd. ex Klotzsch), and New Guinea impatiens (Impatiens hawkeri W. Bull) had a wholesale value of $330 million and were produced from ≈138 million cuttings (National Agriculture Statistics Service, 2007). In this case, the loss of a single cutting is $2.38 lost in potential revenue. Understandably, reducing losses of cuttings during shipping is a critical research interest for cutting producers, plant plug producers, and finished plant producers.
Ethephon [(2-chloroethyl) phosphonic acid] is used on New Guinea impatiens stock plants and many other herbaceous species to increase branching and abscise sink tissues. Ethephon is lipophilic and, on entering the relatively more basic apoplastic environment, undergoes a degradation reaction releasing ethylene, Cl–, and H2PO4– (Warner and Leopold, 1969; Yang, 1969). Application of ethephon results in the abscission of flower buds and flowers, likely as a result of ethylene-mediated promotion of abscisic acid (ABA) synthesis (Goren et al., 1993; Hansen and Grossmann, 2000; Klee, 2002) and subsequent cellulase and polygalacturonase activity (Mishra et al., 2008), thus reducing sink tissue carbohydrate demands. Ethylene-related inhibition of indole-3-acetic acid (IAA) synthesis (Chadwick and Burg, 1970; Weber and Osborn, 1969) is a likely cause of increased branching in both young liners and stock plants (Faust and Lewis, 2005; Hayashi et al., 2001) treated with ethephon.
Stock plant sink tissue management has been critical in lowering cutting losses resulting from carbohydrate depletion during shipping. Rapaka et al. (2008) demonstrated an inverse relationship between cutting carbohydrate content at harvest and subsequent postharvest leaf senescence. Quality of subsequent rooting is also directly proportional to carbohydrate content (Rapaka et al., 2005). Other authors have suggested a correlation between cut flower petal senescence and sugar depletion (van Doorn, 2004).
Problematically, excess ethylene can damage unrooted cuttings by promoting apical meristem necrosis, leaf yellowing, and abscission. Thus, cuttings harvested from ethephon-treated stock plants still evolving ethylene may be exposed to damaging ethylene concentrations during packaging and shipping. Because ethephon-treated plants do not rapidly replace the abscised sink tissues, it may be possible to postpone cutting harvest after ethephon application until ethylene concentrations return to normal. The objective of this study was to investigate the persistence of residual ethephon activity on stock plants and unrooted cuttings. We applied a range of ethephon concentrations and subsequent storage treatments to show how temperature and rinsing of cuttings may affect ethylene evolution.
Foreign Agricultural Service 15 Dec. 2007 U.S. trade imports—FAS commodity aggregations U.S. Department of Agriculture Washington, DC 28 Dec. 2007 <http://www.fas.usda.gov/ustrade/USTImHS10.asp>.
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