The present study was undertaken to find out the optimum concentration and combination of plant growth regulators (PGRs) and their effects on in vitro growth and development of Dendrobium sp. orchid. Protocorm-like bodies (PLBs) were inoculated as explants on MS medium supplemented with four levels (0, 0.5, 2.5, and 5.0 mg/l) of auxin [Naphthalene acetic acid (NAA)] and cytokinin [6-Benzylaminopurine (BAP)] independently to proliferate and multiply the PLBs. Then, these multiplied PLBs were cultured on different concentrations and combinations of NAA (0, 0.5, 2.5, and 5.0 mg/l) and BAP (0, 0.5, 2.5, and 5.0 mg/l) along with 0.5 mg/l kinetin (Kn) for the growth and development of Dendrobium sp. plantlets. The significantly maximum fresh weight and the highest percentage of PLBs were observed from the MS medium supplemented with 2.5 mg/l NAA at both 30 and 60 days after culture (DAC). Similarly, the significantly maximum fresh weight and the highest percentage of PLBs were achieved when MS medium supplemented with 0.5 mg/l BAP and 2.5 mg/l BAP at both 30 DAC and 60 DAC, respectively. In this study, shoots and roots regeneration from PLBs were observed simultaneously at different concentrations and combinations of NAA and BAP with 0.5 mg/l Kn. The significantly highest numbers of leaves (8.3), the longest length of leaves (4.26 cm), and the highest percentage of shoot regeneration (85%) were found from the medium supplemented with 2.5 mg/l BAP + 0.5 mg/l NAA+ 0.5 mg/l Kn. On the other hand, MS medium with the same concentrations of BAP and Kn but a higher concentration of NAA (5.0 mg/l) produced the maximum number of roots (6.17), the longest length of roots (5.10 cm), and the highest percentage of root regeneration (76%). From the findings of this study, these two concentrations and combinations of PGRs (2.5 mg/l BAP+ 0.5 mg/l NAA+ 0.5 mg/l Kn and 2.5 mg/l BAP + 5.0 mg/l NAA+ 0.5 mg/l Kn) found optimum for in vitro culture of Dendrobium orchid. Therefore, these concentrations and combinations of PGRs can be supplemented with the culture medium for mass propagation and conservation of endangered species like Dendrobium orchid.
Key words: Plant growth regulators, In vitro, Dendrobium sp., Orchid, PLBs
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