The Effects of Several Light Sources on Growth and Development in Petunia and Torenia

This study was carried out to investigate the indoor performance of two flowering bedding plants, Petunia ×hybrida ‘Double Wave’ and Torenia fournieri ‘Clown Blue’, under different artificial light sources. Three tube-type (tube) fluorescent lamps (FL) and four LED bulbs were installed at  small frame structures (W80 × D100 × H75 cm), and high pressure sodium lamp (HPS), metal halide lamp (MH), and mercury lamp (MC) were equipped in large frame structures (W80 × D100 × H145 cm). Petunia and torenia seedlings were transplanted into plastic pots filled with soilless mixture, acclimated for one week in a greenhouse, and then placed under the frame structures lighted by the artificial light sources for 10 weeks. Cultural conditions were comprised of 22 ± 2 °C, 25 ± 2 µmol·m^-2·s^-1 PPFD (exceptionally, MC treatment: about 17 µmol·m^-2·s^-1), 16-h photoperiod. Plant height of petunia was respectively high under MH, HPS, and MC, and low under FL tube. Chlorophyll content was high under LED bulb and MH. Number of branches was about five, regardless of light source. Fresh weight was great under MH and LED bulb, and dry weight was most under MH. Flowering percentage was 100% under MH, the others were ≥ 50%, especially 0% under FL tube. Under MH, days to flowering were smallest and the cumulative number of open flowers was much more than the others. Plant height of torenia was highest under MH, that was a little effect of blue light. Chlorophyll content and fresh and dry weights were also high under MH. Flowering percentage was 100% regardless of all treatments. Days to flowering were 23 days under MH and LED bulb, faster than the other sources. Cumulative number of open flowers was ≈10 under LED bulb, MH, and FL tube. As a result, when these flowering bedding plants were introduced interior, proper light source for good performance was MH or LED instead of FL.