Multiple shoot induction from axillary bud cultures of the medicinal orchid, Dendrobium longicornu

Background and aims Dendrobium longicornu, commonly known as the 'Long-horned Dendrobium', is an endangered and medicinally important epiphytic orchid. Over-exploitation and habitat destruction seriously threaten this orchid in Northeast India. Our objective was to develop an efficient protocol for the mass propagation of D. longicornu using axillary bud segments. Methodology and principal results Axillary buds cultured in Murashige and Skoog semi-solid medium supplemented with alpha-naphthalene acetic acid (NAA), 2,4-dichlorophenoxy acetic acid (2,4-D) and 6-benzylamino-purine (BAP) readily developed into plantlets. These formed either directly from shoot buds or from intermediary protocorm-like bodies (PLBs). The maximum explant response (86.6 %) was obtained in medium supplemented with NAA at 30 mu M, while the maximum number of shoots (4.42) and maximum bud-forming capacity (3.51) were observed in medium containing 15 mu M BAP and 5 mu M NAA in combination. Protocorm-like bodies were obtained when the medium contained 2,4-D. The maximum number of explants forming PLBs (41.48 %) was obtained in medium containing 15 mu M BAP and 15 mu M 2,4-D. Well-developed plantlets obtained after 20-25 weeks of culture were acclimatized and eventually transferred to the greenhouse. Over 60 % of these survived to form plants similar to 3-4 cm tall after 90 days in glasshouse conditions using a substrate of crushed brick and charcoal, shredded bark and moss. Conclusions The method described can readily be used for the rapid and large-scale regeneration of D. longicornu. Its commercial adoption would reduce the collection of this medicinally important and increasingly rare orchid from the wild.