Growth and Flowering Responses of Petunia to Various Artificial Light Sources with Different Light Qualities

Abstract

This study was carried out to investigate the effect of artificial light sources with different light qualities on the growth and flowering characteristics of a herbaceous long-day plant, Petunia × hybrida Hort. Seedlings of petunia cultivar 'Madness Rose' were potted, acclimated for one week, and grown in a phytotron equipped with tube-and bulb-type fluorescent lamps (FL tube and bulb), tube-type white light-emitting diodes (LED tube), halogen lamps (HL), metal halide lamps (MH), and high pressure sodium lamps (HPS) for 10 weeks. The temperature, photoperiod, and photosynthetic photon flux density (PPFD) in the phytotron were 22 ± 2 ˳ C, 16 h, and 25 ± 2 µmol ㆍm -2 ㆍs -1 , respectively. Light sources combined with HL promoted stem elongation, and plant height and internode length decreased with increasing red to far-red (R:FR) ratio. FL tube + LED tube, HPS, and FL tube promoted branching, whereas plants grown under light sources combined with HL did not have any branches. Days to flowering (from longest to shortest) occurred as follows: FL tube + HL > FL tube + HL > MH > HPS = FL tube + FL bulb > FL tube + LED tube > LED tube > FL tube, indicating that reducing the R:FR ratio of the light sources promoted flowering. Only 20% of plants grown under an FL tube flowered, whereas under all other treatments, 100% of plants flowered. At 10 weeks after treatment, plants grown under HPS and MH had (cumulatively) 12 open flowers, and those grown under FL tube + FL bulb, LED tube, FL tube + LED tube, and HPS treatment had approximately seven flower buds. These results suggest that light sources with low R:FR ratios promote flowering and stem elongation in petunia, but they reduce its ornamental value due to overgrowth and poor branching.

Investigation on morphology and physiology of potted rose grown with light from microwave-plasma and high-pressure sodium lamps

“…Thus, more resources (e.g., nutrient and soluble sugar) are available per shoot, which have resulted in faster flower development. A lower branching degree and lower ornamental value induced by lower R:FR ratios was also observed in petunia (Park et al, 2016). It could also be excluded that the earlier flowering was due to the increased blue light content in artificial sunlight compared with that in HPS.…”

“…Potted roses grown under artificial sunlight from MPL showed a smaller plant height in both growth environments compared to plants grown under HPS lamps, although a lower R:FR ratio is attributed to an increased stem elongation in the process of shade avoidance (Smith, 1982). An increased stem and leaf elongation by increased far-red light was observed in lettuce and petunia (Lee et al, 2016;Park et al, 2016).…”

“…An earlier flower opening was observed when plants were grown under artificial sunlight in the climate chamber and greenhouse. In long-day plants, such as Arabidopsis, petunia and eustoma, it was shown that far-red light promotes flowering (Cerdán and Chory, 2003;Cerny et al, 2003;Park et al, 2016;Yamada et al, 2009).…”

“…Phytochromes absorb red (R) and far-red (FR) light and occur in two different interchangeable forms, the inactive (P R ) and active (P FR ), depending on the R:FR ratio of the light spectra (Smith, 1982). Lower R:FR ratios under shade conditions lead to shade avoidance syndrome, which is shown by stem elongation, reduced branching and formation of larger and thinner leaves (Casal, 2013;McLaren and Smith, 1978;Park et al, 2016). In contrast, blue light can inhibit elongation growth and lead to the formation of thicker "sun-like" leaves (Cope and Bugbee, 2013;Hogewoning et al, 2010b;Xiaoying, 2012).…”

An Update on Plant Photobiology and Implications for Cannabis Production

“…Exceptionally, it has been reported that reducing the photoperiod to approximately 12 h is a common practice in the cannabis production industry to initiate flowering (Chandra et al., 2017). For other commonly grown flowering plants in the horticultural industry, flowering is initiated via night interruption (Yamada et al., 2008; Blanchard and Runkle, 2010; Park et al., 2016). Both methods initiate flowering; however, reducing photoperiod potentially leads to plant yield reduction.…”