Ethylene promotes leaf yellowing, abscission, and general senescence in unrooted cuttings of Codiaeum variegatum Blume. (croton), Pelargonium ×hortorum Bailey (pro sp.) [inquinans × zonale] (zonal geranium), and Lantana camara L. (lantana) as reported by Müller et al. (1998), Kadner et al. (2000), and Rapaka et al. (2007), respectively. Although ethylene has a negative impact on cutting quality in ethylene-sensitive species, it also plays a critical role in coordinating plant growth under water stress and aiding adventitious root formation (Clark et al., 1999; Mergemann and Sauter, 2000; Sharp and LeNoble, 2002; Stepanova and Alonso, 2005).
Research shows that ethylene injury may be prevented through chemical treatments and environmental management of ethylene-sensitive, floriculture taxa. Treating plant materials with the ethylene biosynthesis inhibitors silver thiosulfate and silver nitrate and the ethylene binding inhibitor 1-MCP have proved useful. Ethylene management has been accomplished through use of perforated packaging to allow ethylene dissipation and 1-MCP sustained release mechanisms (Kadner and Druege, 2004; Kadner et al., 2000; Macnish et al., 2004).
1-MCP disrupts downstream ethylene-mediated developmental signaling by acting as a competitor for ethylene-binding sites (Sisler, 2006). It is widely used in the produce and cut flower industries and is increasingly used on unrooted cuttings (Blankenship and Dole, 2003). 1-MCP prevented leaf yellowing of unrooted cuttings and improved rooting frequency in terminal cuttings of zonal geraniums (Kadner and Druege, 2004; Serek et al., 1998). 1-MCP stimulated ethylene biosynthesis in unrooted geranium cuttings (Kadner and Druege, 2004; Rapaka et al., 2008), and 1-MCP-treated geranium cuttings produced fewer adventitious roots compared with untreated cuttings (Rapaka et al., 2008). Since 1-MCP is a strong competitive inhibitor of ethylene binding, these results indicate that geranium ethylene biosynthesis is regulated by an autoinhibitory feedback mechanism (Kadner and Druege, 2004).
Four experiments were conducted to gain a better understanding of the effect of ethylene and 1-MCP treatments on cutting establishment of several floriculture crop species as such information may be useful for developing practical methods for improving cutting survival and rooting. Expt. 1 tested the two-part hypothesis that, when floriculture crop stem cuttings from a broad range of herbaceous taxa are surveyed, a subset will be found to be ethylene sensitive, and taxa will differ in response to 1-MCP and ethylene pretreatments during vegetative propagation. Expt. 2 tested the hypothesis that exposing cuttings to 1-MCP promotes endogenous ethylene synthesis using five taxa (Euphorbia pulcherrima ‘Visions of Grandeur’, Impatiens hawkeri ‘Sonic Red’, Pelargonium peltatum ‘Mandarin’, P. ×hortorum ‘Kardino’, and Petunia ×hybrida ‘Suncatcher Coral Prism’). Expt. 3 tested the hypothesis that exposing cuttings to 1-MCP affects time to form adventitious roots in six taxa (Angelonia angustifolia ‘Carita Lavender’, Calibrachoa ×hybrida ‘Terra Cotta’, I. hawkeri ‘Sonic Red’, Portulaca oleracea ‘Fairytales Sleeping Beauty’, Sutera cordata ‘Abunda Blue Improved’, and Verbena ×hybrida ‘Aztec Wild Rose’). Expt. 4 tested the hypothesis that 1-MCP and ethylene influence root development in ‘Kardino’ zonal geranium cuttings.
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