Effects of red and far-red fluorescent light on the growth of Gypsophila paniculata plants

The effects of red and far-red irradiation on the growth and flowering of Gypsophila paniculata L. plants were investigated. In the first experiment, plants were grown in phytotrons maintained at day (6:00-18:00)/night (18:00-6:00) temperatures of 17/12degC, 24/19degC, or 30/25degC under a 24-hr photoperiod with 8-hr of natural daylight and 16-hr of artificial lighting with incandescent lamps, far-red fluorescent lamps, or red fluorescent lamps. The plant height was greater and number of days to flowering was less in the case of plants grown under the far-red fluorescent lamp than in those grown under the red fluorescent lamp. Although far-red light accelerated flowering to a greater extent at high temperature (30/25degC) than at low temperature (17/12degC), the quality of the cut flowers was best at low temperature. In the second experiment, the effects of the intensity of far-red fluorescent light were investigated. Plants were grown at day/night temperatures of 17/12degC, 24/19degC, or 30/25degC under a 24-hr photoperiod with 8-hr of natural daylight and 16-hr of artificial lighting with 1, 2, or 4 far-red fluorescent lamps. Far-red light at a high intensity accelerated the increase in plant height and reduced the number of days to flowering, irrespective of temperature. It is expected that high-quality cut flowers can be obtained by cultivating the plants under overnight irradiation with intense far-red light at a low temperature of 17/12degC, although the number of days to flowering is less at high temperature of 30/25degC. In the first experiment, we observed that the number of days to flowering was less in the case of plants grown under the incandescent lamp than those grown under the far-red fluorescent lamp, irrespective of temperature ; this is because the intensity of light from incandescent lamps was stronger than that of light from fluorescent lamps. In the second experiment, the number of days to flowering was identical in the case of the plants grown under 4 fluorescent lamps and those under an incandescent lamp. However, considering the energy exchange efficiency and long life of far-red fluorescent lamps, it is expected that these lamps are a more effective light source.