Poinsettia (Euphorbia pulcherrima Willd. Ex Klotsch.) is a member of the Euphorbiacae family and can grow to 4.5 m tall (Ecke et al., 2004). This plant is popular at Christmas and has been the most popular potted crop until the early 2000s; furthermore, it is currently ranked second among potted plants, with a value of $153 million among states reporting (USDA, 2020). The popularity of this traditional holiday plant can be attributed to the release of new cultivars with improved postharvest life, growth habits, and varying colors and maturity dates (Dunn et al., 2011).
Sales and transportation of poinsettias rely heavily on height, compactness, and branching habit (Alem et al., 2015; Meijón et al., 2009). Most commercially sold poinsettias are free branching and show weak apical dominance in association with poinsettia branch-inducing phytoplasma (POiBI) (Lee et al., 1997). During the past 190 years, breeders have developed cultivars that are much smaller, more compact, and have greater branching than the wild type (Trejo et al., 2012). Many growers today use manual pruning to reduce apical dominance and height while increasing lateral branch growth to achieve good growth habits (Cox, 2001; Larson, 1982). Stimart (1983) reported that branching in poinsettia cultivars is highly variable. The main disadvantage of manual pruning is the high input of labor; however, if done improperly, pruning can reduce the number of flowers of a plant (Sun et al., 2015).
Plant growth regulators (PGRs) are commonly used to control plant growth habit, including plant height and branching, while reducing the time of production and labor costs and improving plant quality (Cohen, 1978; Sajjad et al., 2017). One such PGR is dikequlac sodium, which is absorbed by the leaves and transferred to the tip of the main stem; it inhibits cell division and differentiation in the meristem, leading to reduced apical dominance (Cohen, 1978). Atrimmec contains 18.5% dikequlac sodium and is known to induce lateral branching. Sun et al. (2015) reported that species, rates, and cultural and environmental conditions affect the efficiency of dikegulac sodium on plant growth. The objective of this study was to compare plant growth and branching among pinched, unpinched, and Atrimmec applications on poinsettia ‘Orange Spice’, which shows limited lateral branching.
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Dunn, B.L., Goad, C. & Stanphill, S. 2011 Performance of 40 poinsettia cultivars grown under two different temperatures J. Hort. For. 3 72 77
Grossman, M., Freeborn, J., Scoggins, H. & Latimer, J. 2013 Timing of benzyladenine and dikegulac sodium application affects branching of liners and finished herbaceous perennial plants HortScience 48 875 882 doi: 10.21273/HORTSCI.48.7.875
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Lee, I.-M., Klopmeyer, M., Bartoszyk, I.M., Gundersen-Rindal, D.E., Chou, T.-S., Thomson, K.L. & Eisenreich, R. 1997 Phytoplasma induced free-branching in commercial poinsettia cultivars Nat. Biotechnol. 15 178 182 doi: 10.1038/nbt0297-178
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Sajjad, Y., Jaskani, M.J., Asif, M. & Qasim, M. 2017 Application of plant growth regulators in ornamental plants: A review Pak. J. Agr. Sci. 54 327 333 doi: 10.21162/PAKJAS/17.3659
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Sun, Y., Bi, G., Niu, G. & Perez, C. 2015 Foliar application of dikegulac sodium increases branching of ‘Meritt’s Supreme’ bigleaf hydrangea HortTechnology 25 306 312 doi: 10.21273/HORTTECH.25.3.306
Trejo, L., Arroyo, T.P.F., Olsen, K.M., Eguiarte, L.E., Arroyo, B., Gruhn, J.A. & Olson, M.E. 2012 Poinsettia’s wild ancestor in the Mexican dry tropics: Historical, genetic, and environmental evidence Amer. J. Bot. 99 1146 1157 doi: 10.3732/ajb.1200072
USDA 2020 National Agriculture Statistics Service 10 May 2021. https://www.nass.usda.gov/Publications/Todays_Reports/reports/floran20.pdf