Plant growth regulators (PGRs) are commonly used for ornamental plant production (Whipker, 2013). Among PGRs, triazoles are one of the most popular and effective chemicals for compact ornamental plant production (Arnold, 1998; Jiao et al., 1986; McDaniel, 1990). They have been reported more effective for controlling excessive growth when applied as drench or to stems than as foliar sprays (Davis et al., 1988). However, different triazoles vary in efficacy on same species (Whipker and Dasoju, 1998), different cultivars of same species (Whipker and McCall, 2000), or among different species (Banko and Stefani, 1988). Among triazoles, paclobutrazol effectively controlled excessive plant growth without any phytotoxicity, delayed production, or loss of flower quality of potted zinnia (Chen et al., 1993; Kim et al., 1992; Pinto et al., 2005), marigold (Chen et al., 1993), oleander (Nerium oleander L.) (Bañón et al., 2001; Singh et al., 2004), Curcuma alismatifolia Gagnep. (Pinto et al., 2006), Mussaenda L. (Cramer and Bridgen, 1998), and lavender (Lavandula stoechas L.) (Papageorgiou et al., 2002). Paclobutrazol and ancymidol are closely related nitrogen-containing heterocentric compounds that act on the same three reactions in the gibberellin (GA) biosynthesis pathway (Rademacher, 2000).
Plant growth can be affected by concentration (McDaniel, 1986; Ruter, 1992), application time (Gilbertz, 1992), number of applications (Miranda and Carlson, 1980), application method (Alkhassawneh et al., 2006), formulation/components (Ruter, 1992), and substrate composition (Barrett, 1982). Paclobutrazol was effective in controlling plant size and increasing compactness (Bañón et al., 2001), lowering water use (Hickman, 1986; Ahmad et al., 2014), and decreasing abiotic stresses (Bañón et al., 2006) in ornamental potted and nursery plants. Ancymidol is also used extensively for ornamental plug production and plant growth management (Miranda and Carlson, 1980; Whipker, 2013) or propagation (Maki et al., 2005).
Most PGR studies have focused on controlling plant size and limited work has been reported on secondary effects of PGRs on postharvest durability, plant water or nutrition use, and ethylene sensitivity. A few studies have been reported on the role of paclobutrazol on water stress tolerance in Arachis hypogaea L., C. alismatifolia, and Phillyrea angustifolia L. (Fernandez et al., 2006; Jungklang and Saengnil, 2012; Sankar et al., 2007). However, to our knowledge, no studies have been reported on PGR effect on postharvest durability of bedding plants in pots and plugs.
The specific objectives of this study were to 1) elucidate the effects of two PGRs, paclobutrazol and ancymidol, on postharvest performance of two ornamental potted plants and two plug species and 2) optimize the PGR concentrations for selected floricultural crops. It was hypothesized that use of PGRs would improve postharvest durability by extending shelf life during simulated shipping or marketing.
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