LED Light Quality Drives In Vitro Development of Bletilla striata: Toward Sustainable Orchid Propagation

This study examined the effects of different LED light spectra on the in vitro development of plantlets of Bletilla striata (Orchidaceae), a frost-hardy ornamental orchid with increasing horticultural relevance outside its native East Asian range. The objective was to optimize growth conditions using energy-efficient lighting to support sustainable cultivation practices. Plantlets approximately 4 cm in length with 0.5 cm leaves were cultured on standard Orchimax medium in 200 mL Erlenmeyer flasks and exposed to five LED treatments: 100% blue (B), 100% red (R), red/blue at 70:30 (RB), 50% yellow + RB (7:3), and 50% green + RB (7:3). Fluorescent light served as controls. The photosynthetic photon flux density (PPFD) was maintained at approximately 40 µmol m−2 s−1 across all light treatments. After seven weeks, selected LED spectra improved plantlet performance compared with the control. Leaf number remained stable, while RB light promoted leaf expansion, resulting in the widest leaves. Root formation occurred under all LED treatments, supporting subsequent acclimatization. Light quality strongly affected photosynthetic pigments and secondary metabolism. The highest total chlorophyll content was recorded under RB illumination (581 µg g−1 FW), whereas monochromatic red light resulted in the lowest pigment levels. Carotenoid accumulation was significantly enhanced under RB and RBG spectra. Blue-containing treatments (B and RB) markedly stimulated the accumulation of phenolic compounds, including flavonols and anthocyanins, while red light suppressed phenolic biosynthesis. Total soluble sugars showed an organ-specific response, with red light promoting sugar accumulation in shoots and blue light in roots. These findings demonstrate that targeted LED lighting not only improves plant quality but also offers an environmentally sustainable and economically viable approach for commercial micropropagation and conservation of B. striata.