Biotechnologies in rubber tree (Hevea brasiliensis) : [Draft]

Rubber tree breeding and the dissemination of planting material for plantations are closely linked to propagation methods. Since the progress made by switching from multiplication by seed to propagation by budding, the development of new techniques, such as micropropagation, has been awaited. An analysis of genetic diversity sets out to identify the agronomic traits to be incorporated into the best clones. More widely, genetic modification is a tool that will enable the introduction of new agronomic traits that are not available in the genetic diversity being assessed, and also to optimize the metabolism of the best cultivated clones in a targeted manner. In the next twenty years, a whole raft of innovations is set to contribute to better quality planting material through more efficient rubber tree breeding and propagation processes. Among those innovations, the establishment of a new generation of so-called juvenile budwood gardens is a possibility within the next five years. That transfer will be decisive for assessing the degree to which new technologies are taken on board in modern rubber growing. The involvement of growers and agro-industrialists upstream of the innovation process is decisive for the success of such an undertaking, as for the progress made last century. In vitro culture research has led to three types of micropropagation techniques and genetic modification. Microcuttings. This technique was developed from juvenile seedling material and rejuvenated clonal material by reiterated grafting on young seedling or somatic embryogenesis (Carron et al., 2003). The capacity of that technique therefore depends on the juvenility of the material treated in vitro. Although this procedure is labour consuming, it offers a strong advantage for true-to-type multiplication. Short-term somatic embryogenesis. This technique is now available for about 18 clones worldwide. Although the quality of the emblings is good, the multiplication rate is limited with this method. Long-term maintained somatic embryogenesis. This was the only technique by which mass propagation can be envisaged (Carron et al., 1995b). Although recent work shows this avenue to be highly promising, it is necessary to assess the emblings produced, since the risks of somaclonal variations can be detrimental to the quality of the plant material produced. Genetic modification. This technique combines gene transfer and plant regeneration techniques by micropropagation. In Hevea, gene transfer is possible by particle bombardment, but Agrobacterium tumefaciens is more commonly used, combined with regeneration by somatic embryogenesis (Blanc et al., 2006; Montoro et al., 2000; Montoro et al., 2003). Several cloning strategies can be considered, based on those different micropropagation techniques (Carron et al., 2005). - One-part-tree or self-rooted clones. Clones propagate directly by long-term maintained somatic embryogenesis, or indirectly by microcuttings from emblings produced by short-term embryogenesis (Carron et al., 1995a). (Texte intégral