Abstract
This study was carried out to find the optimal conditions for in vitro polyploid induction of Dendrobium draconis Rchb.f. Seed-derived protocorms of D. draconis were transferred to Murashige and Skoog (MS) medium containing different concentrations of colchicine (0-0.1%, in v/v) and maintained in the dark for 1, 2, 3 or 4 days at 25±2°C. The results showed that prolonged exposure (4 days) of the protocorms to high concentrations of colchicine (0.1%) produced a substantial reduction in their survival percentage and shoot regeneration capacity. Three-day exposure of the protocorms to 0.05% colchicine was most effective in polyploid induction. Only tetraploids were achieved, as suggested by squash technique. Levels of polyploidy induced in D. draconis were confirmed by DNA content and flow cytometry. The obtained polyploid plants had thicker, dark green leaves with larger guard cells when compared to diploid plants. The number of guard cells per unit area observed for the polyploid plants produced is however lower than that found in diploid plants, which might be due to the increase in the size of the guard cells.
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