Photoperiodic responses of Kalanchoe and chrysanthemum to radiation by an infrared lamp

Abstract

This experiment was conducted to investigate the effect of a low intensity infrared radiation on the growth and photoperiodic responses of Kalanchoe blossfeldiana 'Kaluna' and 'Taos', and Dendranthema grandiflorum 'Lemon Eye' grown in growth chambers. In the first experiment, uniformly-rooted cuttings of 'Kaluna' and 'Lemon Eye' were selected and transplanted to 10 cm pots. After a week, pots were transferred from greenhouse to three environment-controlled growth chambers. All chambers were maintained at 25 +/- 1 and 70% RH with an 8 hours photoperiod (760 mu mol center dot m(-2)center dot s(-1)), provided by high pressure sodium and white fluorescent lamps. During the night period one chamber was left unlit (darkness), while the second and third ones were lit with an incandescent lamp (10 mu mol center dot m(-2)center dot s(-1)) or an infrared lamp (15 mu mol center dot m(-2)center dot s(-1)), respectively. Shoot length, root length, stem diameter, number of flowers, number of branches, fresh weight, and dry weight were measured after eight weeks. Flowering occurred on plants maintained in the unlit darkness and under an incandescent lamp during the night period, while only vegetative growth was observed under an infrared lamp. In the second experiment, cuttings of uniformly-rooted 'Taos' and 'Lemon Eye' were selected and transferred from the greenhouse to three environment-controlled growth chambers with the same environment setting as in the first experiment at a week after potting. During the night period one chamber was left unlit (darkness), the second and third ones were lit with an incandescent or an infrared heating lamp, both at a 0.3 mu mol center dot m(-2)center dot s(-1) PPFD level. After nine weeks, flowering in all treatments was observed, but was slightly delayed under an incandescent and an infrared heating lamp. Because both the incandescent lamp and the infrared lamp slightly delayed flowering in these two species, a more detailed experiment is necessary to find out at which intensity and light quality inhibits the flowering of these species.