The management of herbaceous perennial species as stock plants for asexual propagation can be economically beneficial to commercial growers. Uniform vegetative growth and production of numerous shoots for cuttings are ideal qualities for stock plants. To accomplish both growth responses, environmental conditions that induce flowering (e.g., photoperiod or low temperature) must be avoided to inhibit flower induction and promote vegetative growth. Unfortunately, the ability to maintain vegetative growth is a challenge when flowering is not environmentally controlled. For example, Salvia nemorosa L. ‘May Night’ initiates flowers under most environmental conditions, making asexual propagation difficult (unpublished data). Another example is Dianthus caryophyllus ‘Cinnamon Red Hots’, which is a day-neutral plant that perpetually develops flowers under most environmental conditions (Bunt and Cockshull, 1985). In contrast, other perennial plants such as Coreopsis verticillata ‘Moonbeam’ do not require a cold treatment but are obligate long-day plants that flower when the photoperiod is at least 14 h or when a 4-h light break interrupts a long night (Hamaker et al., 2000; Runkle et al., 1998). Although obligate long-day plants remain vegetative under short days, extension growth is also usually inhibited, making cutting production problematic and commercially impractical.
The inability to regulate plant growth and development using environmental signals in some species has led to attempts to chemically control these processes. The plant growth regulator ethephon, which releases ethylene, is used in the floriculture industry to manage herbaceous cuttings, stock plants, and potted crops to inhibit reproductive bud (RB) development, inhibit internode elongation, and stimulate branching. By controlling these plant responses, ethephon has become popular for its ability to streamline crop production schedules in several annual bedding plant crops, including ivy geranium [Pelargonium peltatum (L.) L'Hérit.], New Guinea impatiens (Impatiens hawkeri Bull.), and Fuchsia hybrids (Hamrick, 2003; Whitman et al., 2000). Application of ethephon can eliminate hand removal of flowers, promote and maintain vegetative growth, and reduce labor by an estimated 80% (Konjoian, 1994a). Unfortunately, ethylene does not interact with all species to initiate flower abortion or uniform internode elongation; thus, species-dependent reactions must be investigated.
The objective of this research was to investigate the use of ethephon as a tool to maintain stock plants for perennial species that cannot be otherwise maintained in a vegetative state using environmental manipulation such as photoperiod and chilling. In addition, we tested the hypothesis that ethephon application would increase the number of cuttings harvested, cutting quality, and rooting ability of the cuttings.
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