Bedding plants are the highest revenue sector of the U.S. floriculture industry with a wholesale value over $1.91 billion for the 15 top-producing states (U.S. Department of Agriculture, 2011). Young plants propagated from seed (plugs) or shoot-tip cuttings (liners) are commonly used in herbaceous ornamental annual bedding plant production and propagative material for this use is currently valued at over $166 million (U.S. Department of Agriculture, 2011). Compared with young plants propagated from seed, rooted cuttings have increased genetic uniformity, no juvenile stage to pass before flowering, shorter production time, and the potential to be produced from sterile or seedless cultivars (Erwin, 1994).
The goals of propagators include producing high-quality rooted cuttings by maximizing root growth, total mass, root-to-shoot mass ratio, and stem caliper while minimizing production time and stem elongation (Lopez and Runkle, 2008; Pramuk and Runkle, 2005). To meet the spring and early summer market demand for flowering bedding plants, cuttings are typically rooted in mid- to late winter and early spring when ambient outdoor DLIs are at seasonally low levels (Korczynski et al., 2002). Further reductions in greenhouse DLIs often result from glazing material and interior structures (Hanan, 1998), as well as hanging baskets suspended above benches for additional bedding plant production (Faust, 2004). For instance, greenhouse DLIs across the northern United States in January may be as low as 2−6 mol·m−2·d−1 as a result of reductions of outdoor DLIs by up to 60% (Korczynski et al., 2002; Lopez and Runkle, 2008).
Light impacts growth, morphology, and quality of seedlings (Graper and Healy, 1991; Oh et al., 2010; Pramuk and Runkle, 2005; Torres and Lopez, 2011) and rooted cuttings (Lopez and Runkle, 2008). Although recommendations for light during root development are given in instantaneous units (μmol·m−2·s−1; Dole et al., 2006), photosynthetic photon flux (PPF) varies greatly over a day, month, and season (Lambers et al., 2008; Larcher, 2003), and a more accurate description of PPF during crop production is the integrated photosynthetic DLI, expressed as mol·m−2·d−1.
Lopez and Runkle (2008) quantified the effects of DLI during propagation on Impatiens hawkeri W. Bull (New Guinea impatiens) and Petunia ×hybrida hort. Vilm.-Andr. (petunia). However, the effects of using supplemental lighting to increase DLI during cutting propagation of a broader range of specialty herbaceous annual bedding plants has not been reported. Therefore, our objectives were to quantify the impact of DLI during propagation on growth, morphology, and quality of several vegetatively propagated annual bedding plant species.
Dickson, A., Leaf, A. & Hosner, J.F. 1960 Quality appraisal of white spruce and white pine seedling stock in nurseries For. Chron. 36 10 13
Dole, J.M., Gibson, J.L. & Wilkins, H.F. 2006 Crop-by-crop cutting propagation 229 361 Dole J.M. & Gibson J.L. Cutting propagation: A guide to propagating and producing floriculture crops Ball Publishing Batavia, IL
Faust, J. 2004 Research highlight: The effect of hanging baskets on the greenhouse light environment 36 Fisher P. & Runkle E. Lighting up profits: Understanding greenhouse lighting Meister Media Worldwide Willoughby, OH
Faust, J.E., Holcombe, V., Rajapakse, N.C. & Layne, D.R. 2005 The effect of daily light integral on bedding plant growth and flowering HortScience 40 645 649
Graper, D.F. & Healy, W. 1991 High pressure sodium irradiation and infrared radiation accelerate Petunia seedling growth J. Amer. Soc. Hort. Sci. 116 435 438
Korczynski, P.M., Logan, J. & Faust, J.E. 2002 Mapping monthly distribution of daily light integrals across the contiguous United States HortTechnology 12 12 16
Lambers, H., Chapin, F.S. III & Pons, T.J. 2008 Photosynthesis, respiration, and long-distance transport 11 99 Plant physiological ecology 4th Ed Springer New York, NY
Larcher, W. 2003 The environment and plants 1 67 Physiological plant ecology: Ecophysiology and stress physiology of functional groups 4th Ed Springer-Verlag Berlin, Germany
Lopez, R.G. & Runkle, E.S. 2008 Photosynthetic daily light integral during propagation influences rooting and growth of cuttings and subsequent development of New Guinea impatiens and petunia HortScience 43 2052 2059
Oh, W., Runkle, E.S. & Warner, R.M. 2010 Timing and duration of supplemental lighting during the seedling stage influence quality and flowering in petunia and pansy HortScience 45 1332 1337
Pramuk, L.A. & Runkle, E.S. 2005 Photosynthetic daily light integral during the seedling stage influences subsequent growth and flowering of Celosia, Impatiens, Salvia, Tagetes, and Viola HortScience 40 1336 1339
Ritchie, G.A. 1984 Assessing seedling quality 243 259 Duryea M.L. & Landis T.D. Forest nursery manual: Production of bareroot seedlings Martinus Nijhoff Publishers Hague, The Netherlands
Thompson, B.E. 1985 Seedling morphological evaluation- What you can tell by looking 59 71 Duryea M.L. Evaluating seedling quality: Principles, procedures, and predictive abilities of major tests Forest Research Laboratory, Oregon State University Corvallis, OR
Torres, A.P. & Lopez, R.G. 2011 Photosynthetic daily light integral during propagation of Tecoma stans influences seedling rooting and growth HortScience 46 282 286
U.S. Department of Agriculture 2011 Floriculture crops 2010 summary Nat. Agr. Sta. Service Washington, DC 26 May 2011. <http://usda.mannlib.cornell.edu/usda/current/FlorCrop/FlorCrop-04-21-2011_new_format.pdf>.