Effect of Supplemental Light on Growth, Photosynthesis and Flower Quality of Phalaenopsis ‘Sogo Yukidian V3’

Abstract

Phalaenopsis orchid production is as a flowerpot plant for export and the domestic market in Thailand. Due to Phalaenopsis requires low-temperature condition for growing under temperature-controlled greenhouse, resulting in a high cost of production. Thus, orchid growers have developed the planting methods to save electrical energy by planting the vegetative stage of Phalaenopsis in a semi-open greenhouse under a rain-proof roof and shading net but caused irregular light intensity. Therefore, the objective of this research was to study the effect of supplemental light on the growth, photosynthesis parameters, flowering and flower quality of 14 months age Phalaenopsis ‘Sogo Yukidian V₃’ after deflasking and planting with pine bark. The experimental design was completely randomized design with 5 treatments, including supplemental white LEDs with 100 and 150 μmol m^-2s^-1 during 04:00 to 08:00 a.m. and 04:00 to 08:00 p.m. compared with control (only natural light) for 4 months. The results showed that supplemental light did not affect leaf growth, but caused the changes in the diurnal CO₂ exchange rate and stomatal conductance compared with control. Supplemental lighting at 04:00–08:00 a.m. resulted in earlier CO₂ exchange about 2–4 hours (12:00 p.m.–04:00 p.m.) in phase IV, while supplemental lighting at 04:00–08:00 p.m. increased CO₂ exchange in phase II, but decreased it in first 2 hours of phase I and inhibited it in phase IV. The 4 months supplemental lighting before induction of inflorescences did not affect time to flower, inflorescence number, flower number and flower size. However, the supplemental light at 150 μmol m^-2s^-1 light intensity had total CO₂ uptake higher than at 100 μmol m^-2s^-1.