Growth characteristics and flowering initiation of Phalaenopsis Queen Beer ‘Mantefon’ as affected by the daily light integral

Abstract

This study was conducted to determine the effects of daily light integral (DLI) levels with different photoperiods and light intensities on the growth and flowering initiation of Phalaenopsis plants. Five-month-old Phalaenopsis Queen Beer ‘Mantefon’ plants were treated with combinations of three photoperiods [8/16 (day/night, short day, SD), 12/12 (medium day, MD), and 16/8 h (long day, LD)] and three light intensities in the range of photosynthetically active radiation of 50, 100, and 200 μmol·m−2·s−1, resulting in DLI levels ranging from 1.44 to 11.52 mol·m−2·d−1 with warm-white LEDs at 28°C during the vegetative period. Additionally, 12-month-old plants were treated with combinations of three photoperiods [8/16 (day/night, SD), 8 + 8/8 (day-extension (DE); an extension with 10 μmol·m−2·s−1 for 8 h right after the SD), and 16/8 h (LD)] and three light intensities (75, 150, and 300 μmol·m−2·s−1), resulting in DLI levels ranging from 2.16 to 17.28 mol·m−2·d−1, at 20°C during the forcing period for flowering. During the vegetative period, plants showed a tendency of overgrowth in leaves, via the formation of long and narrow leaves, as the light intensity decreased, irrespective of the photoperiod. The number of new leaves, total leaf area, and shoot and root dry weights increased with increasing photoperiod and light intensity, implying an increase in the amount of light energy. During the forcing period, photoperiodic effects on flowering initiation were not observed, while increasing the light intensity increased the number of inflorescences and accelerated spiking. The DLI showed higher correlation coefficients with growth and flowering initiation characteristics than those of the photoperiod or light intensity alone. New leaf emergence, biomass accumulation, and spiking were enhanced as DLI levels increased, although these positive effects were gradually saturated. These findings indicated that the DLI is a major factor in the growth and flowering initiation of Phalaenopsis plants and increasing DLI levels can promote growth or flowering initiation of these plants. These findings will be useful in controlling light conditions to maximize the growth rate and shorten the cultivation time in Phalaenopsis cultivation.