Effects of wavelength of LED-light on in vitro asymbiotic germination and seedling growth of Bletilla ochracea Schltr. (Orchidaceae)

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The effects of different light wavelengths on in vitro asymbiotic germination of mature seeds and seedling growth of Bletilla ochracea Schltr. were examined using five wavelengths from light emitting diodes with peak wavelengths of 470 nm (blue), 525 nm (green), 590 nm (orange), 625 nm (red), and from white light emitting diodes at 40 μmol m−2 s−1. Gellan gum solidified New Dogashima medium without plant growth regulators was used as germination medium. Cultures were maintained at 25°C under 24 h continuous lighting or darkness. The frequencies of seed germination three weeks after sowing reached more than 60% in all light conditions examined including continuous darkness. The highest frequencies of seed germination of 74% were achieved using lighting both with green and orange light emitting diodes, though strong inhibition of seed germination by the specific wavelength was not recognized. Seedling growth of this species was greatly inhibited by darkness. The most effective wavelength of light for rhizoid formation was revealed to be in the range of 590 nm (orange light) and 625 nm (red light), and almost no rhizoid was formed in the darkness. After 3 months of culture, leave width was expanded under white and blue light emitting diodes and was narrower under green, orange and red light. Seedlings grown under white and blue light emitting diodes resulted in thicker pseudobulbs.