Ethylene influences development and flowering of Ptilotus spp. in vitro and ex vitro V. Andriessa Prameswara a , Margaret Johnston a, *, Melinda Perkins a , Victor Robertson b , Diah Ratnadewi c a Centre for Native Floriculture, School of Land, Crop and Food Sciences, The University of Queensland, Gatton, QLD 4343, Australia b School of Land, Crop and Food Sciences, The University of Queensland, Gatton, QLD 4343, Australia c Department of Biology, Bogor Agricultural University, Bogor 16151, Indonesia 1. Introduction Ptilotus (Amaranthaceae) is an Australian native genus con- sisting of around 100 species of annuals, perennials and subshrubs (Anon, 1997, p. 721). Some species have been identified as having ornamental potential as a cut flower, potted plant and/or land- scaping plant (Harrison et al., 2006). These species tend to have a long flowering period, tolerate drier growing conditions and produce inflorescences which exhibit a long vase life. The horticultural potential of Ptilotus has been recognised for many years, but the difficulty of obtaining viable seed and poor germination of some species has limited their wider cultivation (Williams, 1996). Micropropagation may provide a means of overcoming these issues (Williams and Taji, 1990), but Ptilotus often becomes floral in vitro and this causes the plantlets of P. spicatus and P. nobilis to elongate (Harrison et al., 2006). Elongation increases the length of the plantlet but not the number of new shoots, reducing the number of new plantlets generated at each subculture. Vegetative propagation of Ptilotus ex vitro is also difficult due to a lack of vegetative material. The vegetative phase is very short and difficult to manipulate. The visible bud stage of P. nobilis occurred in 22 days under high light intensity (909 mmol m À2 s À1 ) and in 28 days under a light intensity of 398.6 mmol m À2 s À1 (Orzek et al., 2009). Induction does not appear to be regulated by temperature or daylength (Johnston, 2006). Research to improve the plantlet quality and multiplication rate in vitro and the quality and cutting yield of stock plants ex vitro is essential for commercial propagation of Ptilotus. Ethylene may either promote or inhibit flowering, depending on the plant species and cultivar. Foliar application of ethephon (2- chloroethylphosphonic acid, an ethylene-releasing compound) to control flowering of stock plants has been investigated for a number of ornamental species. It has been shown to reduce inflorescence number in Impatiens (Tamari et al., 1998), Monarda and Leucanthemum (Hayashi et al., 2001), and delay flowering in Echinacea, Monarda and Physostegia (Hayashi et al., 2001). Reports on the effects of ethylene on in vitro inflorescence production are limited. However, one investigation reported that Scientia Horticulturae 122 (2009) 227–232 ARTICLE INFO Article history: Received 3 December 2007 Received in revised form 23 March 2009 Accepted 6 May 2009 Keywords: Amaranthaceae Ethephon Headspace Ptilotus nobilis Ptilotus spicatus Vegetative propagation ABSTRACT The genus Ptilotus has immense potential for ornamental horticulture but its commercial development has been hindered by propagation limitations. Poor seed quality and germination are reported. Cutting propagation is limited by cutting supply as the juvenile phase of Ptilotus is short. Micropropagation has been used in an attempt to overcome these difficulties but explants become floral in vitro and this causes plantlets to elongate. Ethephon has been used to control flowering of stock plants of many ornamental species. This study investigated the effect of ethephon applied to young (3-week-old, deflasked from tissue culture) and mature (1-year-old) Ptilotus plants in a greenhouse. A system of applying gaseous ethylene at 0, 100, 200 and 300 mg l À1 to the headspace of in vitro plantlets in glass jars was developed and the response of in vitro plantlets to ethylene studied. One-year-old Ptilotus plants were treated with 500 mg l À1 ethephon 2 days before pruning or 1 or 2 weeks after pruning. Ethephon application 2 days before pruning decreased the number of inflorescences and increased the number of shoots (compared to the control) but was phytotoxic. Ethephon applications of 150 or 300 mg l À1 applied weekly or fortnightly to 3-week-old plants deflasked from tissue culture reduced plant height and number of inflorescences and at low concentrations increased the number of new shoots. A fortnightly application at 150 mg l À1 is recommended. Previous reports on the effects of ethylene on inflorescence production on plantlets in vitro are limited. Our study showed that exposure of in vitro plantlets of P. nobilis to ethylene gas at 100 mg l À1 for 1 h significantly increased the number of shoots and plant height but this did not occur for plantlets of P. spicatus. Plantlets of P. spicatus exposed to transient ethylene at 200 and 300 mg l À1 showed significantly greater rooting (52.4%) than the control (13.6%). ß 2009 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +61 7 5460 1240; fax: +61 7 5460 1112. E-mail address: m.johnston@uq.edu.au (M. Johnston). Contents lists available at ScienceDirect Scientia Horticulturae journal homepage: www.elsevier.com/locate/scihorti 0304-4238/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.scienta.2009.05.004