In vitro propagation and clonal fidelity assessment of Rhynchostylis retusa (L.) Blume: a threatened ornamental and medicinal orchid

Rhynchostylis retusa (L.) is an epiphytic orchid with high medicinal and ornamental potential. It is commonly known as ‘Queen of Orchid’ and ‘fox tail orchid’. The present study was designed to standardize an efficient protocol for the mass multiplication of R. retusa and to assess the clonal fidelity of the in vitro regenerated plants. The R. retusa seeds were inoculated into basal MS, half and quarter strength MS medium and showed maximum 89% germination in MS medium after 4-weeks of incubation. The protocorm like bodies were developed from seeds after 6-months of incubation. Protocorms inoculated into MS medium fortified with BAP (4.4 µM) and activated charcoal (2.0 g l⁻¹) were observed to be optimal medium for shoot proliferation in R. retusa and maximum 46.84 shoots with a 6.5 cm shoot length were obtained. The in vitro regenerated shoots exhibit maximum 97.64% root proliferation in half-strength MS medium enriched with activated charcoal (2.0 g l⁻¹) and 7.4 roots per shoot with 6.7 cm root length were obtained. The properly developed plantlets were successfully acclimatized with 80% survival. Clonal stability of the protocol was evaluated by using 20 RAPD markers, which proved true for the typesets of the in vitro raised plants. Thus, the present study optimized an in vitro propagation system for R. retusa which can be successfully applied for germplasm conservation, genetic improvement studies and commercial scale propagation of the species for medicinal and ornamental purposes.