Flowering of Euphorbia pulcherrima Willd. ex Klotzsch var Valenciana under blue and red LED light

Abstract

Objective: To determine the effect of blue light (BL) and red light (RL), applied five hours at the end of the day (AED) and that of temperature, on the flowering of Euphorbia pulcherrima var Valenciana.

Design/Methodology/Approach: Three groups of plants were established under greenhouse conditions, all received sunlight (SL), AED one was under BL (460 nm) and another under RL (660 nm) with a photosynthetically active photon flux of 440 µmol m^-2 s^-1 and 550 µmol m^-2 s^-1 respectively; from the beginning of the experiment until 144 d later. In a second flowering cycle, residual effects of the treatments were evaluated.

Results: In the first flowering cycle, the appearance of cyathia and bract pigmentation under BL occurred on average at 177.5 d after initiation of the treatments, and under RL at 178 d. Compared to the application of SL alone (138 d) the process was delayed, on average 39 and 40 d, under BL and RL, respectively. No residual effects of the treatments on flowering were recorded.

Limitations on study/implications: It is necessary to evaluate other levels of temperature below and above the ones reported in this study, and also to increase and decrease the photoperiod.

Findings/conclusions: The prolonged delay in flowering can be attributed not only to the quality and intensity of light, but also to the photoperiod and the daytime temperature above that documented for flower initiation in var Valenciana.