Blanketflower is an herbaceous annual in the Aster family. It is native throughout Florida (Wunderlin and Hansen, 2004) and most of the United States (U.S. Department of Agriculture, 2006), with cultivated varieties grown worldwide. Using blanketflower (Gaillardia pulchella) and common gaillardia (G. aristata) as parents, more than 30 cultivars have been produced that vary in floral attributes, flowering time, vegetative characteristics, cold tolerance, and landscape performance (Schoellhorn, 2004). The ornamental value of blanketflower is further revealed by its use in many state university trial gardens including University of Georgia, Colorado State University, North Carolina State University, Auburn University, Pennsylvania State University, and even in Canada at the University of Guelph. In 2005, The University of Florida “trialed” 23 blanketflower cultivars and ecotypes and found that two of the Florida ecotypes (from Leon and Okaloosa counties) had greater or equal landscape impact than many of the cultivated selections (Danielson, 2005).
Many of the blanketflower cultivars available today can be propagated by seed in addition to cuttings. Although relatively easy to produce, blanketflower is fast growing and can quickly reach a cumbersome size for handling and shipping. Applications of plant growth regulators (PGRs) may help to extend the amount of time these plants can be held before distribution and sale, to improve visual quality, and to facilitate shipping. There are many PGRs available for use on ornamental crops, but their effectiveness is often species or even cultivar specific (Barrett, 2001; Chamberlayne and Banko, 2003; Hilgers et al., 2005; Keever and Olive, 1994; Kim et al., 1999; Latimer et al., 2006). To our knowledge, no information has been reported for chemical plant growth regulation of blanketflower, with the exception of ‘Burgundy’ blanketflower (G. ×grandiflora), of which G. pulchella is a parent. Thomas et al. (1998) and Latimer et al. (1999) found that PGR response of burgundy blanketflower varied by application rate, application number, and PGR type. We conducted a preliminary study with a blanketflower ecotype (G. pulchella) and a cultivated selection of ‘Torch Flame’ blanketflower (G. pulchella) to determine how three commercially available PGRs [daminozide (B-Nine; Uniroyal Chemical Co., Middlebury, CT) daminozide/chlormequat chloride (Cycocel; Olympic Horticultural Products Co., Mainland, PA), and paclobutrazol (Bonzi; Syngenta Crop Protection, Inc., Greensboro, NC)] affect plant growth and flowering, and found none of these PGRs to be effective in controlling plant growth (Danielson, 2005). The cultivar Torch Flame is a Ball Selection (Ball FloraPlant, West Chicago) characterized by having heat-tolerant, long-lasting blooms with trumpet-shaped ray florets in hues of yellow, red, and orange on well-branched, upright plants. The Florida ecotype has a looser growth habit and fewer ray florets that are horizontally oriented. There is a potential market for local or regional ecotypes in landscape plantings as public awareness and use of native species has become more widespread (Florida Wildflower Advisory Council, 2004; Hammond et al., 2007; Norcini and Aldrich, 2004).
In addition to daminozide, daminozide/chlormequat chloride, and paclobutrazol, two other commonly used chemical growth retardants are uniconazole (Sumagic; Valent USA Corp., Walnut Creek, CA) and Ethephon (Florel; Southern Agricultural Insecticides, Palmetto, FL). Similarly to daminozide, uniconazole inhibits the synthesis of gibberellins, but often at a lower concentration and with greater efficacy (Barrett, 2001). Ethephon is an ethylene-releasing compound that has been used to suppress height in some species (Krug et al., 2006; Rademacher, 1991). The objective of the current study was to determine whether uniconazole or ethephon, used at varying rates with one or two applications, can reduce plant size of cultivated and noncultivated forms of blanketflower.
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