Ex vitro and in vitro Paphiopedilum delenatii Guillaumin stem elongation under light-emitting diodes and shoot regeneration via stem node culture

Paphiopedilum spp. are high value horticultural crops; however, success in Paphiopedilum spp. culture is still limited. It is therefore necessary to find out adequate solutions to improve the culture techniques of these recalcitrant species. In the present study, ex vitro shoots exposed to LEDs for shoot elongation and in vitro multiplication of P. delenatii from single nodes were investigated. One-month-old ex vitro shoots with 1.5–2.0 cm length were grown under various light conditions including monochromatic blue and red LEDs, mixtures of blue and red LEDs, and the darkness for investigations of the shoot elongation. The results indicated that the best stem elongation was obtained under monochromatic blue LED (100B) after 4 months of culture. The highest shoot regeneration rate (45 %) was also recorded in shoots cultured on liquid SH medium containing 30 g l-1 sucrose, 1.0 mg l-1 TDZ and 0.3 mg l-1 NAA with cotton wool plug as the substrate and exposed to 100B after 45 days. P. delenatii young shoots, which had formed 5 leaves, were placed into SH medium supplemented with 0.5 mg l-1 - BA, 0.5 mg l-1 NAA, 30 g l-1 sucrose, and 1 g l-1 activated charcoal in the darkness for stem node elongation before transferred into greenhouse. After 120 days, the average shoot length was 10.5 cm, and five new leaves and five single nodes per shoot were observed. These shoots then were maintained under fluorescent light for 60 days. Although the shoots regenerated new leaves, no new node was observed. After 180 days of culture, each shoot was cut into five single nodes, and cultured on fern fibers. These shoots showed to grow vigorously after 12 months.