Effect of germination media on in vitro symbiotic seed germination of three Dendrobium orchids

In vitro symbiotic seed germination has become increasingly popular for orchid propagation. With very few exceptions, in vitro symbiotic seed germination methods use oat meal agar (OMA) as the medium. However, effects of oat concentrations on symbiotic germination of orchid seeds have not been investigated. In our first experiment, effectiveness of three concentrations of ground oat (1, 5, or 10 g/l) in OMA inoculated with an orchid mycorrhizal fungus (Tulasnella deliquescens (Juel) Juel), uninoculated OMA (10 g/l of oat) and one fifth Murashige and Skoog medium containing 6 g/l of sucrose (1/5MS) on promoting seed germination of Dendrobium lindleyi Steud. were compared. Germination and protocorm development of D. lindleyi were found to be enhanced by higher oat concentrations. The OMA containing 10 g/l of oat with mycorrhizal inoculation also outperformed 1/5MS. In our second and third experiments, the use of common orchid cultivation substrates as alternative media for in vitro symbiotic orchid seed germination was investigated. For Dendrobium fimbriatum Hook., we demonstrated that sphagnum peat moss inoculated with T. deliquescens either isolate Da-KP-0-1 or Pv-PC-1-1 in plastic containers could be used to germinate the orchid to advanced seedling stage, although the germination percentages were low, probably due to the waterlogged characteristic of the peat moss and low ventilation of the plastic boxes. For Dendrobium findlayanum C.S.P. Parish & Rchb.f., we used the mixture of peat moss and coir dust packed in Petri dishes to solve the mentioned problems and compared the effectiveness of this system to OMA and 1/5MS. The three treatments resulted in similar germination percentages but the symbiotic methods were more effective than 1/5MS in promoting protocorm development of D. findlayanum. The findings of this study can be used to improve symbiotic germination media and they encourage the use of symbiotic germination method as mean for orchid seed propagation.