In vitro Propagation of Thuja occidentalis ‘Sunkist’, an Ornamental Tree of Cupressaceae

Thuja occidentalis ‘Sunkist’ (Cupressaceae) is one of the most commonly planted ornamental tree cultivars in parks, gardens or urban green areas due to its attractive appearance and low maintenance requirements. In this study, we optimized an efficient protocol for in vitro propagation of this cultivar. To establish the aseptic cultures, stem segments 1.5–2.0 cm long with axillary buds were inoculated on Murashige and Skoog (MS) medium supplemented with 0.2 mg L−1 1-naphthaleneacetic acid (NAA), 0.5 mg L−1 6-benzyladenine (6-BA), 500 mg L−1 polyvinylpyrrolidone (PVP), 30 g L−1 sucrose and 5.0 g L−1 agar and then grown under fluorescent lamps with a light intensity of 1800 lx, resulting in the in vitro shoot induction of 63.7%. In vitro shoots were successfully multiplied on modified MS medium supplemented with 0.5 mg L−1 kinetin (KT) and 0.1 mg L−1 indole-3-butyric acid (IBA) under light condition of mixed LEDs (Blue/Red 1 : 7) with a light intensity of 1200 lx, resulting in the shoot multiplication rate of 3.7 fold and the shoot vitrification rate of 0%. In vitro shoots were successfully rooted on 1/4 modified MS medium, resulting in the root induction rate of 70.5%. In vitro plantlet height suitable for greenhouse acclimatization was 2.5–3.5 cm, the adequate acclimatization medium was a mixture of vermiculite, carbonized rice husk, peat, coal ash and fermented sawdust (the volume ratio was 2 : 4 : 2 : 1 : 1), the appropriate sun light intensity and temperature were 5000 lx and 20–25°C, respectively, and the suitable light intensity and period for field-hardening were 30 000 lx and 7–9 d, respectively.