Production of poinsettia (Euphorbia Pulcherrima) with light emitting diodes compared with the traditional high pressure sodium lamp

Abstract

Use of chemical are commonly used as tools for the commercial pot plant producers to grow strong, dwarfed, and compact plants. Although, these growth regulators have adverse effects on human health and the environment. So, this issue has motivated researchers to search for alternative methods for growth regulation. The aim of this study was to test light emitting diodes (LEDs) with different light qualities alone or in combination with high pressure sodium lamps (HPSs), to investigate their effects on compactness, flowering time and transpiration of poinsettia (Euphorbia pulcherrima). Similarly, to understand more of the growth regulation, hormone analysis was performed on some of the plant material. Two experiment, one in a growth chamber experiment and one in a greenhouse compartment were performed at SKP (Senter for Klimaregulert Planteforskning), Norwegian University of Life Science (NMBU). The growth chamber experiment was conducted to compare growth and hormonal content (auxin, abscisic acid, cytokinin and gibberellin) of shoots developed with HPS and compared with LED (20% blue and 80% red). However, LED with 20% blue and 80% red light used in the growth chamber experiment did not induce differences in morphology or hormonal content of poinsettia cv Christmas Eve compared to the traditionally HPS. In the greenhouse compartment experiment to assess effect of LEDs (blue LED and Green LED) alone or in combination with HPS towards compactness in cv Christmas Day HPS + blue (150 +50 µmol m-2 s-1) and HPS +green LED (150 + 50 µmol m-2 s-1) have a potential to reduce shoot length in poinsettia compared to HPS (200 µmol m-2 s-1) alone but the results were dependent on the background irradiance from natural light. Green light reduced transpiration, chlorophyll content in leaves and anocyanin content in bracts compared to blue light and reduce the external quality. Flowering time in poinsettia is very robust and no differences in flowering time was observed in any of the experiments. Thus it is concluded that blue LED in combination with HPS light are efficient in reduction of plant height without changing the flowering time and will to improve the external quality compared to green LED.