Effect of technique and darkness on the success of meristem micrografting of Picea abies

The possibility of micrografting in vitro shoot meristems of #Picea abies# were investigated on a 18 year-old Norway spruce clone. The rates of success were shown to be greatly influenced by the grafting technique used and by light, with a positive effect of a 2 to 3 week darkness period applied to the stocks just after they had been grafted. Average scores of more than 50% of success were obtained. However, substantial variability in terms of shoot expansion among the grafted plants existed in vitro, as well as after transfer to ex-vitro conditions. (Résumé d'auteur

Rubber tree clonal plantations: Grafted vs self-rooted plant material

The forest tree species Hevea brasiliensis is extensively planted in the humid tropics to meet the increasing demand for natural rubber. Huge quantities of planting stock are therefore needed. The seed option remains the easiest and cheapest way to establish plantations of rubber trees but those show a great variability for vigor and also for latex yield. The rationale of producing clones for overcoming this variability was already obvious in the early 1910's but due to the difficulties encountered at that time for rooting shoots, grafting was used as an alternative cloning method. The striking increase in yield noticed from the graft-derived clonal plantations warranted their large scale development. Eventually, the budded clones by virtue of their much higher and uniform productivity supplanted the seedlings in most industrial plantations. However, grafting is also associated with drawbacks and for decades efforts aiming at mass producing selected rubber tree clones on their own roots by rooted cuttings have been pursued. However, this approach was progressively abandoned due to disappointing rooting results and, from the 70's onwards, priority has been given to in vitro methods which were booming during this period. But despite 40 years of heavy investments, industrial H. brasiliensis clones could still not be mass micropropagated in vitro efficiently enough to meet the requirements of large scale production. The situation may change radically soon, however, due to the development of new nursery techniques adapted to the mass clonal production by rooted cuttings of any H. brasiliensis selected genotype. Efforts to improve the techniques as well as the establishment of new field trials are underway in order to determine if self-rooted rubber tree clones are more productive than grafted ones. This old issue is becoming of overriding importance considering the increasing pressure on land availability reducing thereby the prospects for expanding rubber tree plantations. (Résumé d'auteur

Possible mass production options for Acacia mangium plantations in Sabah (Malaysia)

Acacia mangium est considéré comme une espèce majeure de reboisement au Sahab pour ses capacités à réhabiliter les sites dégradés et sa croissance remarquable. En conséquence, il est urgent de déterminer les options les plus appropriées de production de masse pour remplir les besoins immédiats et la demande croissante de plants de reboisement. Malgré une absence totale d'information sur les modalités d'hybridation de l'espèce due à sa très récente domestication, des gains substanciels peuvent être attendus de stratégies simples basées sur la reproduction sexuée, prennant en compte le fait qu'Acacia mangium est une espèce se reproduisant très tôt et abondamment et répondant de façon satisfaisante à la sélection de provenance. D'autre part, la propagation clonale est handicapée par des effets négatifs de la maturation sur les possibilités de clonage des génotypes sélectionnés. Une solution intéressante pourrait consister en la sélection de familles-plus parmi des familles de la meilleure provenance aux races définies par des tests de descendance, puis utiliser la multiplication végétative pour établir des vergers de clones comme populations de production des arbres d'élite sélectionné

Microgreffage du séquoia géant

Différents aspects du microgreffage de Sequoiadendron giganteum sont analysés. La mise au point d'une technique détaillée permet de greffer des méristèmes d'individus centenaires sur de jeunes semis cultivés in vitro. Les résultats obtenus sont discutés en relation avec les phénomènes de rajeunissement. La technique proposée paraît applicable à de nombreux secteurs de la biologie, aussi bien en recherche fondamentale que dans des domaines plus appliqués. (Résumé d'auteur

Micropropagation and production of forest trees

Forest tree species have been micropropagated in vitro for nearly 50 years by axillary budding first, then with increasing interest by de novo organogenesis, i.e., adventitious budding and somatic embryogenesis. The particularities of these three main techniques and more generally of in vitro micropropagation are reviewed, analyzing their respective pros and cons as well as their effectiveness and limitations for mass producing improved quality planting stock by comparison with more conventional propagation methods. (Résumé d'auteur