In vitro growth of Quercus robur L. buds taken from 1-7 month old seedlings or adult plant material was studied. The following were investigated for their effects on the establishment of explants and subsequent subcul~res: original position and lignification of the primary explant, conditioning and ageing of source plants, incorporation of N 6 benzyladenine (BA) and activated charcoal in the medium.For bud break the best results were obtained with explants from herbaceous twigs in all tested media. For shoot growth the results depended on the medium used. Medium containing activated charcoal produced episodic growth, leaf organogenesis was reduced, spontaneous rooting occurred, but subculturing from adult plant material failed. On medium containing more than 8.8/aM of BA, all the buds developed abnormally and elongation did not occur. At lower concentrations of BA (4.4/aM) shoots elongated, leaf organogenesis was increased and episodic growth tended to disappear on subcultured seedling explants. No spontaneous rooting was observed, but subculture from adult plant material was managed successfully.

Shoot growth, shoot multiplication in vitro, and rooting of shoots were compared in 6 clones derived from adult trees originating from a single plot in a french forest and in 16 clones derived from seedlings originating in the NE of France or in the Netherlands. The results showed strong within-provenance variations affecting shoot growth, multiplication factor, number of subcultures that could be achieved and, for the clones from adult trees only, frequency of shoots that rooted. In contrast, significant between-provenance differences could not be shown.

Summary — This paper describes a method of in vitro culture establishment from shoot-tip explants taken from juvenile and mature plant material for oak (table I). The cultures established from shoot-tips were then compared with cultures derived from nodal explants for decontamination, their initial reactivity and their potential for long-term propagation. For the decontamination, the results showed that the use of shoot-tip explants is useful only when culture establishement must be made directly from source-plants growing in situ (table II). Otherwise, the use of nodal explants taken from source-plants that are maintained under active growth and controlled sanitary conditions is more advisable due to a better initial reactivity. As regards the potential for long-term propagation, the culture establishment from shoot-tips appeared truly interesting only in the case of recalcitrant clones and/or insufficient optimization of the culture methods (fig 1). However, this positive effect attenuated after a 6-7 month culture period, and the clonal effects and the management of the media became the determining factors of the culture behaviour whatever the initial explant used (fig 2).

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