Scientia Horticulturae 184 (2015) 171–178 Contents lists available at ScienceDirect Scientia Horticulturae journal h om epage: www.elsevier.com/locate/scihorti Red and blue light effects on morphology and flowering of Petunia × hybrida Pramod Gautam, Meseret Tesema Terfa, Jorunn Elisabeth Olsen, Sissel Torre ∗ Norwegian University of Life Sciences, Department of Plant Sciences, P.O. Box 5003, 1432 Ås, Norway a r t i c l e i n f o Article history: Received 29 June 2014 Received in revised form 30 December 2014 Accepted 7 January 2015 Available online 5 February 2015 Keywords: Flowering FR-deficient film Light-emitting diodes Plant morphology Petunia a b s t r a c t To investigate the effects of R and B in environments with different FR levels, Petunia × hybrida ‘Tidal wave’ were grown in a greenhouse during early spring (March) and late spring (May) under plastic film transmitting (+FR) and not transmitting far-red light (-FR) in combination with R and B light emitting diodes (LED) as supplementary light placed underneath the films. The main objective of the study was to test the effect of R (600–700 nm, peak 660) and B light (400–500 nm, peak 450) on morphology and flowering in a FR-deficient greenhouse environment compared with an environment with FR light in different seasons. R light reduced shoot elongation and resulted in more compact plants in both seasons and the combination of –FR and R light resulted in the most compact plants without much delay in flowering. By contrast, the effect of B light was dependent on the natural background light level and the presence of FR light. In early spring when the natural irradiance was low (1.35 mol m -2 h -1 ), B light promoted stem elongation, caused a more upright shoot orientation, increased plant height and promoted flowering compared to control and R light, whereas in late spring, when the natural irradiance was higher (2.33 mol m -2 h -1 ), the effect of B light in a FR-deficient environment was not significantly different from R light in the response to stem elongation and flowering. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Control of morphology and flowering are important in the pro- duction of high-quality bedding plants. Plant growth regulators (PGRs) are commonly used by growers to grow compact plants (Rademacher, 2000). Due to negative impacts on the environment and expected future restrictions on the use of PGRs, there is a strong need for alternative strategies and other tools to control plant shape (Sørensen and Danielsen, 2006). Environmental factors such as temperature, light, watering, mechanical stress and fertilization are well known to modify plant morphology. However, manipulation of some of these factors may be difficult to implement during plant production and some factors may delay or inhibit flowering like temperature manipulations (Langton and Horridge, 2006; Myster and Moe, 1995). Flowering of Petunia × hybrida is accelerated under photo- periods longer than 12 h but is also sensitive to irradiance and light quality (Adams et al., 1999). High irradiance as well as far-red (FR) light promote flowering but induce unwanted stem elonga- tion growth (Adams et al., 1999; Kubota et al., 2000; Patil et al., ∗ Corresponding author. Tel.: +47 64965628. E-mail address: sissel.torre@nmbu.no (S. Torre). 2001). Manipulation of light is a central topic in greenhouse pro- duction and important in optimization of photosynthesis and as a signal in photoperiodic and photomorphogenic responses of plants. The ability of plants to sense and respond to light depends on their photosynthetic pigments and photoreceptors that absorbs differ- ent wavelengths of the light. Responses to light quality like FR (700–800 nm) and red (R) light (600–700 nm) are acting via the light-absorbing pigment phytochrome, which is sensing the rela- tive amount of R and FR light in the environment (Smith, 2000). Blue (B) light (400–500 nm) is also absorbed by phytochrome but also via the B/UV-A absorbing pigment cryptochrome and phototropin (Lin, 2000). In petunia, R light has been found to suppress plant height and flowering but stimulates lateral shoot elongation. In contrast, B light increased shoot elongation and promoted flowering of petu- nia (Fukuda et al., 2011). However, the experiment of Fukuda et al. (2011) was carried out in closed growth chambers at rather low irradiance (100 mol m -2 s -1 ) without natural light. In other stud- ies performed in greenhouses, B light was found to suppress stem elongation growth of roses and poinsettia (Islam et al., 2012; Terfa et al., 2013). In addition, a B light-deficient environment has been found to promote stem elongation in many long-day plants (LDP) (Runkle and Heins, 2001). However, in chrysanthemum, the effect of B light on plant height was found to be dependent on the http://dx.doi.org/10.1016/j.scienta.2015.01.004 0304-4238/© 2015 Elsevier B.V. All rights reserved.