Résumé
The Mediterranean citrus industry face up to an increasing combination of biotic and abiotic constraints. Soon the spread of Citrus Tristeza Virus and its vector Toxoptera citricida all over the area will prohibit the current use of the traditional sour orange rootstock, that provide adequate tolerance to salinity and alkalinity. Therefore, there is an urgent need to select new citrus rootstocks. All the required tolerance traits are present in citrus germplasm. An Euromediterranean MPC INCO project has started in 2006, between Spain, Morocco, Tunisia, Turkey and France to enhance the efficiency of citrus germplasm exploitation for rootstock breeding. Beside applied aspects (implementation of two regional networks for germplasm management and agronomical evaluation of new rootstocks), genomic and molecular physiology are two main components of the project, focusing on tolerances to salinity and iron deficiency associated with alkaline soils. Candidate genes are searched from ESTs data base (ionic transport, osmotic protection, oxidative stress protection...) and by the study of gene expression of tolerant and susceptible genotypes by microarrays and cDNA-AFLP analysis. Specific macroarrays for tolerance will be made to analyse candidate gene expression for a larger range of genotypes. Allelic diversity of candidate genes is studied by SSCP, ecotilling and sequencing. Finally, the candidate genes will be positioned on genetic maps of Citrus and Poncirus and physical map of Clementine. (Texte intégral)