Vegetative Growth and Inflorescence Emergence of Phalaenopsis 'Mantefon' as Affected by Photoperiod, Light Intensity, and Daily Light Integral

Abstract

This study was conducted to deterimne how photoperiod, light intensity, and daily light integral (DLI) influence vegetative growth (Experiment 1) and inflorescence emergence (Experiment 2) in Phalaenopsis. In Experiment 1, five-month-old plants were treated with a combination of three photoperiods [8 (short day, SD), 12 (medium day, MD), and 16 h (long day, LD)] and three light intensities (50, 100, and 200 μmol∙m-2∙s-1), resulting in 7 DLIs ranging from 1.44 to 11.52 mol∙m-2∙d-1. Each light treatment was maintained for 20 weeks at constant 28oC. It was observed that plants grown under longer photoperiod and high light intensity resulted in shorter, wider, and thicker leaves, respectively. Number of new leaves, total leaf area, and shoot and root weights were increased with increasing photoperiod and light intensity. DLI showed higher correlation coefficients with vegetative growth parameters than with photoperiod and light intensity. The regression analysis indicated that increased DLIs promoted vegetative growth. However, it was observed that when DLI reached 11.52 mol∙m-2∙d-1, response slope gradually decreased. In Experiment 2, twelve-month-old plants were used to investigate the effects of photoperiod, light intensity, and DLI on inflorescence emergence. Plants were treated with combinations of three photoperiods [8/16 (day/night, SD), 8+8 (DE

10 μmol∙m-2∙s-1 for 8 h extension right after the SD), and 16/8 h (LD)] and three light intensities (75, 150, and 300 μmol∙m-2∙s-1). Each light treatment was maintained for 12 weeks at constant 20oC. Inflorescence emergence percent, the days to emergence, and the number of inflorescences were generally more promoted under LD treatments than SD and DE treatments, indicating that the effect of photoperiod on flower induction of Phalaenopsis was insignificant. Comparing the light intensities, inflorescence emergence was generally promoted as the light intensity was increased. Correlation coefficients of DLIs with days to emergence and number of inflorescences showed the highest values. Regression analysis indicated that as DLI increase from 2 to 17 mol∙m-2∙d-1, the days to inflorescence emergence was shortened by about one month, and average number of the inflorescence was increased more than 2 times. However, they seemed not to be promoted beyond DLI of 12 mol∙m-2∙d-1, suggesting that the DLI reached the maximum (or saturation) point. Thus, inflorescence emergence was promoted with increasing DLI, but the DLI above 12 mol∙m-2∙d-1 was less promotive for inflorescence emergence.