The production of shoot-tip cuttings for the greenhouse ornamental industry in the United States primarily occurs in South and Central America. Therefore, the success of U.S. growers has become increasingly dependent on their ability to receive high-quality cuttings from offshore production facilities. However, shipment of cuttings usually takes 2 or 3 d from the time they are harvested from stock plants and are available for rooting. In addition, shipment often occurs under unfavorable conditions such as temperature extremes and exposure to ethylene (Purer and Mayak, 1988). Ethylene production is stimulated by many forms of stress, which eventually results in leaf senescence and abscission (Abeles et al., 1992). As a result, rooting in propagation can be inhibited after quality deterioration during shipment.
Although ornamental plants propagated from vegetative cuttings have become increasingly important, little is known about the postharvest physiological processes that occur in unrooted cuttings of many species. Most of the published research has focused on methods for improving the storage longevity of cuttings by delaying postharvest leaf abscission and senescence. Investigations include the use of cold storage treatments (Behrens, 1988) and application of ethylene action inhibitors such as 1-methylcyclopropene (1-MCP), silver nitrate, and silver thiosulfate (Blankenship and Dole, 2003; Faust and Lewis, 2005; Kadner and Druege, 2004; Paton and Schwabe, 1987; Serek et al., 1998). Additional studies include application of gibberellins (Purer and Mayak, 1988) and thidiazuron (Mutui et al., 2005).
Lantana camara L. ‘Dallas Red’ is an evergreen shrub valued for its colorful flowers ranging from yellow to red. Lantanas are mainly produced as mixed bedding, border, and container plants. In lantana, leaf abscission and shoot apices blackening are frequent quality problems usually observed during postharvest shipment or storage of cuttings.
Studies on tomato seedlings (Lycopersicon esculentum Mill.) have shown that chilling sensitivity was highest at the end of the diurnal dark period (King et al., 1988). Furthermore, in different species of fresh herbs or leafy green vegetables, it was demonstrated that the shelf life of leaves can be extended by harvesting at the end of the photoperiod (Clarkson et al., 2005; Lange and Cameron, 1994). Those responses were attributed to the endogenous carbohydrate levels of the tissue. In plants, carbohydrates have conventionally been viewed as resources for respiration, metabolic intermediates, and osmotic functions as well as structural or storage components. However, carbohydrates also modulate gene expression (Koch, 1996) and several other vital processes that are also controlled by hormones (Sheen et al., 1999). There are studies indicating an interaction between carbohydrates and ethylene signal transduction pathway (Leon and Sheen, 2003; Zhou et al., 1998). For example, Yanagisawa et al. (2003) demonstrated that glucose enhances the degradation of the ethylene-insensitive 3, a key transcriptional regulator in ethylene signaling. In addition, external loading of sucrose decreased ethylene responsiveness in harvested broccoli (Brassica oleracea L.) florets and carnation (Dianthus caryophyllus L.) flowers (Nishikawa et al., 2005; Verlinden and Garcia, 2004). However, no similar ethylene studies have been reported on vegetative cuttings.
The objectives of this study were (1) to determine whether harvest time would influence subsequent storage quality of unrooted lantana cuttings, (2) to determine the effect of preharvest carbohydrate status of cuttings on postharvest ethylene action, and (3) to evaluate the effect of 1-MCP treatment on postharvest storage quality and final rooting response.
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