Innovation and scaling-up in micropropagation: lessons from the oil palm experience

In the mid-seventies, the first results obtained by the strategy of reciprocal recurrent selection (RRS) of oil palm (Elaeis guineensis Jacq) and the emergence of the methods of cloning by in vitro culture led to the development of a technique of micropropagation through somatic embryogenesis which was tested initially in Côte d'Ivoire, then in Malaysia and Indonesia. This work established the utility of clonal micropropagation which was found to enable the production of high yielding clones. In addition, this development phase highlighted the difficulties related to scaling-up in relation to, on the one hand, mass production required to meet the needs of planters and, on the other hand, the genetic fidelity of the regenerated plant material. These two concerns led us to look further into the underlying mechanisms involved in somatic embryogenesis and the somaclonal variation events induced by the regeneration techniques. The development of a regeneration protocol based on the use of embryogenic suspensions has generated a method which allows production on a large scale of single somatic embryos. This method is now widely used for commercial micropropagation and it is currently field tested by several companies. In order to tackle the problem of the mantled flowering abnormality which is induced during the oil palm micropropagation process we have carried out studies of gene expression in tissue cultures as a means of establishing an early clonal conformity testing procedure. More, our studies on genomic DNA methylation changes induced by tissue culture suggest that the latter may play a key role in the determination of the mantled abnormality. We demonstrated, by the use of two complementary methods for evaluating methylation rates at the genome-wide level, that there is a highly significant DNA hypomethylation in leaves of abnormal regenerants and calli, compared to their normal counterparts. New investigations are now aimed at elucidating the mechanisms and/or sequences through which epigenetic misregulation could provoke the onset of the mantled phenotype in oil palm. Our experience in oil palm micropropagation revealed the pivotal importance of the pilot stage in the identification of both biological and technological bottlenecks for the large scale production. Once transformed in adequate questions to research, the identified problems are able to stimulate innovation and improve our knowledge on the biology and physiology of palms. (Texte intégral