Vegetatively propagated herbaceous bedding plants are produced in two distinct phases: a young plant stage, in which shoot-tip cuttings are rooted as liners, and a finish plant stage, in which the rooted young plants are transplanted into a larger finish container where they are grown until they become marketable (Klopmeyer, 2003). Vegetative propagation of bedding plants occurs from mid to late winter and early spring when average daily ambient photosynthetic DLI is typically low, especially in northern latitudes (Currey et al., 2012; Lopez and Runkle, 2008). During this time, outdoor DLI can range from 5 to 20 mol·m−2·d−1 (Korczynski et al., 2002). Shading, glazing materials, obstructions, and structures can further reduce DLI within propagation facilities to 2.5 to 10 mol·m−2·d−1 (Oh et al., 2010) and can be as low as 1 mol·m−2·d−1 during extended periods of overcast weather (Lopez and Runkle, 2008).
Many studies have been performed on the effects of increasing DLI during the young plant stage on root and shoot biomass, liner, and plug transplant quality (Currey et al., 2012; Enfield, 2002; Graper and Healy, 1991; Lopez and Runkle, 2008; Pramuk and Runkle, 2005; Rapaka et al., 2005; Torres and Lopez, 2011) or during the finish plant stage on flowering (Fausey et al., 2005; Islam et al., 2005; Loehrlein and Craig, 2004). Generally, increases in DLI during the propagation of seedlings and cuttings increased biomass accumulation, root growth, and transplant quality and hastened subsequent flowering. For example, increasing propagation DLI from 4.1 to 14.2 mol·m−2·d−1 during the seedling stage increased shoot dry mass per internode linearly by 64%, 64%, 47%, and 68% and plants subsequently flowered 4, 10, 12, and 12 d earlier in Tagetes patula L., Celosia argentea var. plumosa L., Impatiens walleriana Hook. f., and Viola ×wittrockiana Gams., respectively (Pramuk and Runkle, 2005). When Petunia ×hybrida Vilm.-Andr. and Viola seedlings were provided with supplemental light (≈4 to 5 mol·m−2·d−1) during the last two-thirds or entire young plant stage, shoot dry mass and number of leaves increased, whereas subsequent time to flower decreased. Similarly, increasing propagation DLI from 1.2 to 10.7 mol·m−2·d−1 increased the root and shoot dry mass of Impatiens hawkeri Bull. ‘Harmony White’ cuttings by 1038 and 82%, respectively, and subsequent time to flower decreased from 85 to 70 d, respectively (Lopez and Runkle, 2008).
When outdoor DLI is low, the only way to increase DLI is to provide supplemental lighting from high-intensity discharge lamps (Oh et al., 2010). Lopez and Runkle (2008) indicated that DLI should be maintained between 4 to 6 mol·m−2·d−1 when Impatiens hawkeri and Petunia cuttings are stuck and during callusing. The DLI should increase between 6 and 8 mol·m−2·d−1 during root development and toning to obtain rapid, uniform rooting and high-quality rooted transplants that flower earlier, especially when cuttings are rooted during the darkest periods of the year. When ambient DLI is 8 to 10 mol·m−2·d−1 or less, Oh et al. (2010) recommend using supplemental lighting during the two true leaf stage to produce good-quality plugs, rapid flowering, and energy savings.
One report (Lopez and Runkle, 2008) quantifies the effects of ambient DLI during vegetative cutting propagation on subsequent growth and development during the finish stage. 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 published. Therefore, our objective was to quantify the impact of supplemental DLI during cutting propagation on subsequent growth and development of four annual bedding plant species.
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