Effect of Light Combination and Timing of Supplemental Lighting on Growth Characteristics and Flowering of Pansy (Viola × wittrockiana Rose)

The goal of this study was to examine how different light combinations and timing of supplemental lighting affect the vegetative and reproductive responses of pansy (Viola × wittrockiana Rose). The present study was designed as a factorial experiment based on a completely randomized block design with three replications and two factors of timing of supplemental lighting (night-interruption and day-extension) and light combination treatments consisting of different proportion of blue (B, 467 nm) and red (R, 625 nm) light with high pressure sodium lamp (HPS) serving as control. The light combination treatments (65 mmol m-2 s-1) included 100% R, 85% R: 15% B, 70% R: 30% B, and HPS. Our results showed that the plants exposed to 85% R: 15% B had the highest foliage fresh and dry weights (2.06 g and 0.23 g), stem diameter (1.42 mm), leaf area (44.72 cm2), and leaf number (16.5), and plants exposed to 100% R had the highest root fresh and dry weights (1.63 g and 0.39 g) and height (6.17 cm), respectively. The results showed a significant interaction between light combination and the timing of supplemental lighting on Chl a, Chl b, Chl total, and carotenoids contents and flowering time. Night-interruption supplemental lighting in exposure to 85% R: 15% B led to the highest Chl a (0.86 mg g-1 FW), Chl b (0.52 mg g-1 FW) and Chl total (1.51 mg g-1 FW) contents. The highest carotenoids content (0.69 mg FW) was obtained from night-interruption supplemental lighting under 70% R: 30% B. Night-interruption supplemental lighting was related to the shortest time to flowering (56 days after seed sowing), but it did not differ significantly from day-extension supplemental lighting under 70% R: 30% B.