Easter lily is an important flowering potted crop in the United States, with a wholesale value over $26 million for the 15 largest-producing states (U.S. Department of Agriculture, 2007). Plant height can reach up to 1 m and must be controlled to produce plants 48 to 56 cm tall for aesthetic value and amenability for packing and shipping (Miller, 1992, 1993).
Height control of easter lily may be achieved environmentally, culturally, or chemically (Blom et al., 1995, 2004; Erwin et al., 1989; McAvoy, 2001). Stem elongation may be reduced environmentally by manipulating the difference between the day and night air temperatures—also known as DIF (Erwin et al., 1989). Increasing light intensity and reducing exposure to far-red–enriched light at the end of the day (twilight) are additional environmental techniques for reducing easter lily stem elongation (Blom et al., 1995). Reduction of easter lily stem elongation may be achieved culturally with overhead irrigation using cold water from shoot emergence to flowering (Blom et al., 2004). While these environmental and cultural techniques may be used during easter lily production, they may be difficult to employ in greenhouses with multiple crops or limited infrastructure. Alternatively, chemical plant growth retardant (PGR) applications may used to produce compact potted easter lilies (McAvoy, 2001).
Several PGRs have been reported to produce shorter easter lilies, including ancymidol, ethephon, paclobutrazol, and uniconazole (Bailey and Miller, 1989; Gianfagna and Wulster, 1986; Jiao et al., 1986; Larson et al., 1987; Lewis and Lewis, 1980, 1981, 1982; Sanderson et al., 1975; Wilfret, 1987, 1990; Wilfret and Reiser, 1996). While PGRs are commonly applied as sprays or media drenches, bulb crops may be submerged in PGR solutions before planting (bulb dip). Bulb dips can reduce labor costs and avoid reduced efficacy associated with drench applications to substrate components, including bark (Barrett, 2001; Miller, 1993).
Bulb dips have been reported to be an effective method of applying PGRs to control height of numerous bulb crops, including hyacinth (Hyacinthus), paperwhites (Narcissus), and tulips (Tulipa) (Krug et al., 2005a, 2005b, 2006). Easter lily height also has been successfully suppressed in response to bulb dips, yet only solutions containing ancymidol or uniconazole have been used (Larson et al., 1987; Lewis and Lewis, 1980, 1981, 1982; Wilfret, 1990). Paclobutrazol has effectively reduced easter lily stem elongation when applied as a drench or spray (Gianfagna and Wulster, 1986; Jiao et al., 1986; Wilfret, 1987; Wilfret and Reiser, 1996). Dipping oriental lily (Lilium auratum × Lilium speciosum) and LA-hybrid lily (L. longiflorum × asiatic Lilium spp.) bulbs in paclobutrazol solutions has successfully controlled plant height (Francescangeli et al., 2007; Ranwala et al., 2002, 2005); however, we have found no reports of dipping easter lily bulbs in paclobutrazol solutions.
Our objectives in this study were to determine if dipping ‘Nellie White’ easter lily bulbs in paclobutrazol solutions would suppress final plant height and produce a commercially acceptable plant while not adversely impacting days to flower and flower bud number.
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U.S. Department of Agriculture 2007 Floriculture and nursery crops yearbook: Report 9 Sept. 2009 <http://www.ers.usda.gov/Publications/Flo/2007/09Sep/FLO2007.pdf>.