Recommendations for light during commercial greenhouse crop production is often reported in μmol·m−2·s−1, an instantaneous measurement of light intensity (Dole and Wilkins, 2005; Hamrick, 2003). However, light intensity varies greatly within a single day and over the course of a growing season (Lambers et al., 2008; Larcher, 2003). Therefore, the integrated photosynthetic DLI expressed in moles per day is a more accurate description of light during crop production as it is the cumulative light received over the course of a day (Fausey et al., 2005).
Commercial producers of potted and bedding plants aim to decrease total production time and maximize flower number and biomass of flowering plants. The DLI during crop production has been reported to affect these traits. For example, as the DLI increases, the time to flowering and node number below the first flower decrease, whereas flower number and dry weight gain increase for many bedding plant species (Faust et al., 2005; Mattson and Erwin, 2005; Warner and Erwin, 2005). Similar results have been reported for potted flowering crop species including cyclamen [Cyclamen persicum (Oh et al., 2009)], hibiscus [Hibiscus spp. (Warner and Erwin, 2003)], and kalanchoe species (Carvalho et al., 2006; Zimmer, 1985).
The majority of potted and bedding plant production in the United States occurs in the fall, winter, and early spring (Garland et al., 2010). This is the time of year when ambient outdoor DLIs are at seasonally low levels (Korczynski et al., 2002). Inside the greenhouse, DLI is further reduced because of greenhouse glazing and interior structures (Hanan, 1998). During these periods with low DLIs inside the greenhouse, commercial producers must decide whether to provide supplemental irradiance to produce high-quality finished plants. However, species vary in their DLI requirement with respect to crop quality (Faust, 2003). Therefore, it is important to identify how irradiance during production affects growth, development, and ornamental quality when evaluating germplasm for introduction as a new floriculture crop (Roh and Lawson, 1998; Wilkins and Erwin, 1998).
The genus Kalanchoe contains 139 species (Descoings, 2005). We identified several kalanchoe species with potential as new ornamental potted and/or bedding plants: K. glaucescens ‘Freeling's Sensation’, K. manginii, K. laciniata, K. nyikae, K. rotundifolia, and K. velutina (Currey, 2009). These species have ornamental potential on the basis of unique plant form, foliage, flowers, and/or inflorescences. The objective of our research was to identify the effect of the DLI on growth and flowering of six kalanchoe species with desirable ornamental characteristics.
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