Résumé
The Plant Biotechnologies and Genetic Resources Programme at CIRAD uses the latest technologies to make optimum use of plant genetic diversity, and thus to boost variety improvement operations of a wide range of tropical crops in a large array of environments. Biotechnology research for tropical crops develops new methods for optimum genetic resource management, facilitates the creation and identification of elite genotypes and participates in the rapid dissemination of selected varieties. The essential basis is a rational use of genetic diversity available from germplasm collections and the refinement of gene incorporation or introgression methodologies through accurate genome mapping, marker-assisted selection and/or cloning and genetic transformation. The strength of these activities rests on efficient collaborations with partners from the South, in both the public and private sectors, and integrated research on stations in the tropics. Such research is mainly successful because it is demand-oriented, based on a multidisciplinary approach, and often conducted, within a frame of international collaborations, in close involvement with other genotyping, transgenesis, robotics and cellular imagery units, and serve as a basis for innovative research, for adaptation before effective transfer to the research stations overseas, and for training. - Molecular analysis of genetic diversity being used for the constitution of core collections permits a better characterisation of the genomic richness of the species, including its cytoplasmic components, and a linkage to genetic mapping. Genome dosage, interspecific recombination and gene introgression are often the key to quality materials and breeding efficiency of a number of tropical crops which are derived from interspecific hybrids, both of natural and artificial origin. In situ hybridization on plant chromosomes was developed in order to study these aspects in particular crops such as sugarcane and banana-plantain. - Genome mapping and tagging of genes involved in traits of agricultural interest are performed thanks to the virtually unlimited number of tags offered by molecular markers. Original saturated maps have been developed for banana, cocoa, eucalyptus, rubber tree, oil palm, sorghum and sugarcane. Research is connected to field experiments in the tropics and under laboratory controlled conditions for dissecting the genetic control of the major breeding target traits. A major effort is directed towards studying the resistance to biotic stresses, in connection with molecular analyses of the pest and pathogen diversity also performed. Depending on the genetic control of traits, these studies evolve more or less rapidly towards fine mapping and gene cloning. In the most advanced cases, genetic analysis is relayed by physical mapping using BAC libraries within collaborative projects. - Micropropagation is of a special interest in this case of woody species predominantly allogamous where the "elite plants" cannot be multiplied through seeds or even through classical horticulture. Somatic embryogenesis, especially with cell suspensions, offers a powerful tool for multiplication. Mastering the whole process for a true-to-type multiplication, taking into account the risk of somaclonal variation, and using embryogenic cell suspensions as targets for genetic transformation are actual priorities for tropical crops. - Genetic transformation experiments have started on several plants: banana, coffee, cotton and rice. These systems are being used for testing promoter and gene action. Besides the efforts aimed at cloning genes from the target plants, CIRAD has developed activities using the bacteria Bacillus thuringiensis (Bt) to try and control important pests. A particular effort has been placed on screening toxins (and genes) available from the many different strains of Bt and constructions especially adapted for genetic transformation of monocots or dicots have been made up. (Texte int