In vitro asymbiotic seed germination of Dendrobium nobile varied significantly with fruit harvesting time and growth medium used for culturing seeds. Seeds harvested 129 days after pollination (DAP) possessing globular shaped embryos and a discontinuous cuticle layer showed a substantially greater germination on P668 medium. Alternatively, immature seeds harvested 96 and 116 DAP displayed a significantly lower germination response on various growth media. Most of the ovules at 96 DAP are in archesporial and megaspore mother cell stages, whereas the majority of ovules are mature and fertilized at 116 DAP. Mature seeds harvested 158 DAP also germinated at a higher frequency at Stage 5 (emergence of the first leaf) after 8 weeks of culture on different growth media indicating the absence of testa imposed dormancy in this endangered epiphytic orchid.

The effects of explant and cytokinin types on in vitro plant regeneration of Ansellia africana were investigated. The exogenous addition of cytokinins is not required for the proliferation of new protocorms from Trimmed protocorm cluster (TPC) explants. To the contrary, nodal and shoot-tip explants produced a single shoot in response to the addition of cytokinins. Overall plant growth in terms of shoot length, leaf number, frequency of root organogenesis, root length, and fresh weight/plant were significantly higher in media containing meta-Topolin Riboside (mTR) in both nodal and shoot-tip explants. Thidiazuron (TDZ) and 6-benzyladenine (BA) induced stunted and hypertrophied shoots at their highest level (15 lM). In addition root differentiation and root growth were significantly lower on P668 media with TDZ and BA. Zeatin was capable of inducing a significantly higher root organogenesis frequency and root length in TPC explants as compared to other cytokinins. However, TPC explants produced a significantly greater number of longer shoots ([3 cm) on P668 media with mTR. Hyperhydric shoots were produced from TPC explants. The occurrence of hyperhydricity is discussed with respect to the culture vessel used in this study.Keywords Adventitious shoot Á Ansellia africana Á Hyperhydricity Á meta-topolin riboside (mTR) Á Trimmed protocorm cluster (TPC) Abbreviations BA 6-benzyladenine DMRT Duncan's multiple range test mTR meta-topolin riboside P668Phytotechnology medium TDZ Thidiazuron TPC Trimmed protocorm cluster

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