Effects of light quality on the flowering responses inKalanchoe blossfeldiana

Abstract

Light is one of the most important environmental factors and has at least three aspects; intensity, photoperiod and quality. There are many studies of the influences of light intensity and the photoperiod on flowering responses. Those results led to the development of novel practical technology for the control of flowering. However, there are many still unexplained phenomena on the light quality. Kalanchoe (Kalanchoe blossfeldiana Poellniz.) is well known as a typical qualitative (obligate) short-day (SD) plant and it has been used as experimental material for the flowering response. Thus, the flowering responses of two cultivars of kalanchoe, 'Arena' and 'Cora', were studied under the following light regimes: SD under four different light emitting diodes (LEDs), white, blue, green and red; SD under natural light + light extension (LE; 7 h from midnight); SD under natural light + photoperiod extension (12 h; 6:00-18:00) with supplementary LED lighting (four colours as above). In the case of LE, the flowering was completely inhibited under each light quality. Under SD, the earliest flowering occurred under red light. Blue light considerably delayed flowering. In contrast, photoperiod extension (to the critical photoperiod for kalanchoe) with blue light caused a distinct flowering response but there was no flowering under supplementary red and green light. It is concluded that the flowering of kalanchoe is mainly controlled by red light. The direct flowering response to blue light was weak but blue light had a secondary or indirect effect.