The effect of light spectrum and thidiazuron plant regulator on embryogenesis and photosyntesis system of phalaenopsis orchid

Phalaenopsis (Phalaenopsis amabilis) is a kind of tropical orchids that in recent years has been very popular as a pot and cut flower plants in the Iranian market. Due to Specific methods of cultivating and inability of plantlet producing in our country, growers have to import Phalaenopsis seedlings from other countries. Despite many problems such as transport losses, hard quarantine, high prices and production costs, import of plantlets have always been increasing. Introducing of new cultivars with high quality, beauty and attractiveness to satisfy world markets, had led to strengthen and intensify of this permanently dependence. Finding a way to reproduce the cultivars of this plant is the first step to get rid of this dependency. therefore, goal of this research was assessment of the effects of light spectra, plant growth regulators and wounding effect to find suitable conditions for inducing somatic embryogenesis and mass clone production of this plant.

To conducted this research, after seed culture, 3-month-old in vitro protocorms were used as explant which cultured in cutted and intact form on a 1/2 MS medium containing 0 and 3 mg g-1 TDZ concentrations and were exposed to six Lighting treatments include (Blue, Red, White, Green, Blue-Red, Red+ Far-red that supply of LED lamps) and Dark condition too, for 4 mounth. subculture were repeated every 3 weeks. Twice imaging of fluorescence has done to evaluation of the maximum efficiency of photosynthetic II (QY-max).

The results showed that different light spectra and plant growth regulator affected the inducing and formation of embryos but wounding had no effect on embryo induction. Intact protocorms had The highest percentage of direct embryogenesis (100%) in treatment with 3 mg L-1 TDZ and Red+ Far-red spectrum without significantly difference compared to red spectrum. The lowest rate of embryogenesis was observed in Blue spectrum, Dark condition and Blue-Red spectra, respectively. In the first imaging the highest QY-max level was observed in blue light treatment and in the second imaging, the highest QY-max was observed in white and green light treatments.

use of the red-red optical spectrum with plant growth regulator (TDZ) is generally recommended for the successful induction of embryogenesis in this kind of orchid. According to the fluorescence measurement of chlorophyll in somatic embryos, blue spectrum for embryo inducing and then white or green spectrum for embryo development can be used to achieve the maximum efficiency of the photosynthetic system.