The rootstock clones in rubber tree: a new varietal type toward the rejuvenated bi-clone

Cloning rubber rootstocks by microcutting will remove the genetic variability of the seedling rootstocks; Moreover, it will open the way to the breeding of rootstock clones regarding main challenges as the growth-vigor of the trees, the water stress tolerance or the root diseases tolerance. In other respects, using rejuvenated selected clones for budding will counteract the weakening effect of ageing. The conventional rubber clones are two-parts trees built up by budding mature budwood of selected clones [trunk and canopy] on unselected and uncloned seedling rootstocks [root system]. Outputs from biotechnology on Hevea brasiliensis, make it possible now to create the "rejuvenated biclone" associating a new rootstock clone A with a rejuvenated budded clone B. Such "bi-clone" will allow to optimize each part of the tree and their specific interaction; thus making the propagation more reliable and with higher quality regarding growth and rubber yield. This paper gathers laboratory and field data which grounded this project. The cloning of young seedlings by microcutting was previously defined by the CIRAD team in France since 1988 and more than 50.000 vitroplants were produced then. Field development of such self-rooted vitroplants was analysed at the CNRA research centre, in Ivory Coast, during ten years for growth and rubber yield. Results give evidence for the conformity of the root system and for the vigorous development of these trees which could have been used as clonal rootstocks. Work in progress with Michelin shows that rejuvenated budded clones, issued from primary somatic embryogenesis, display higher growth speed than the conventional mature clones. Currently, the IBRIEC and IRRI teams, in Indonesia, are successfully implementing the same microcutting process. The first "bi-clones" have been built and planted at Bogor early in 2008, showing the feasibility of it. (Résumé d'auteur