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Rhododendron simsii 'Hellmut Vogel' was regenerated using different types of explants, auxins and cytokinins. After a callus induction phase, with 2,4-dichlorophenoxyacetic acid or a-naphthaleneacetic acid, adventitious shoot regeneration was obtained on a medium supplemented with thidiazuron or zeatin. With thidiazuron shoots were small and a subsequent elongation step was required before rooting. An elongation step was not required when zeatin was used. The duration of the callus induction phase was negatively correlated with the regeneration capacity.

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In vitro polyploidy induction offers the possibility of quick multiplication over in vivo methods, and is therefore particularly interesting for slowly growing plants. Three different in vitro protocols for the induction of tetraploid Rhododendron simsii hybrids were evaluated. The most successful technique was a daily application of mitotic poison on the apical meristem of seedlings. However, this technique was quite labour intensive. Direct sowing on media enriched with antimitotic agents requires less work but is less efficient. To induce ploidy chimeras starting from an existing genotype, mitotic inhibitors can be added to multiplication media. Abbreviations COL (colchicine), DAPI (4,6-diamidino-2-phenylindol), LSD (least significant difference), ORY (oryzalin), PAR (photosynthetic active radiation), TRI (trifluralin)

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