Effects of Light Quality, Daylength and Growing Temperature on Flowering in Morning Glory (Pharbitis nil Choisy)

Abstract

Seedlings of a typical short-day plant, morning glory (Pharbitis nil Choisy cv. Violet) were exposed to different light qualities under a 16-h light period, which was longer than the critical daylength. Flowering occurred in blue light, but not at all under the light qualities of green, red or white. Irradiation with white light (consisting of 50% blue light) for 14h per d also promoted flowering, while white light supplemented with near ultraviolet (UV-A) light had no effect on flowering. These results suggest that cryptochromes, blue-light receptors, influences flowering in morning glory under long-day conditions. Phytochromes did not seem to have any relation to flowering. Besides, after the investigation on growing temperatures of 18, 23 or 28°C under a 12-h light period, it was found that light quality hardly influenced flowering at 18°C, and flowering responses under blue light were promoted at 23°C especially. Stem elongation was significantly inhibited under blue light and under white light supplemented with UV-A.