Résumé
The advantages of clonai plantations are obvious for a lot of tree species. Somatic embryogenesis is a clonai propagation method with the greatest potential for achieving this goal, especially if combined to genetic engineering. However, more than for other vegetative propagation techniques, the practical use of somatic embryogenesis remains strongly impeded by the genetic identity and the physiological age of the mature selected trees to be cloned. So far, somatic embryogenesis has been successfully obtained from mature individuals only for a very limited number of broad-leaved or deciduous species using as primary explants leaves in a proper physiological condition and also sporophytic tissues from the reproductive organs. It is currently still limited to the embryonic phase of the ageing process for many evergreen coniferous species of high industrial impact. Shoot apical meristems owing to their key role in phase change warrant special consideration for attempting to clone mature trees by somatic embryogenesis. If direct induction from in situ collections is still hazardous in the absence of reliable indicators for the more responsive physiological stage, preconditioning in vitro procedures are worth considering when attempting to succeed in somatic embryogenesis from mature trees. These in vitro techniques include serial microcutting in subcultures as well as meristem culture and micrografting. With these techniques meaningful results have been obtained for different tree species in terms of rejuvenation. If some are limited to in vitro conditions, others are more unequivocal. (Résumé d'auteur)