Résumé
The predominance of sour orange rootstock in the Southern and Eastern part of the Mediterranean Basin is presently threatened by the spread of Citrus Tristeza Virus (CfV) and the dispersion of its main vector Toxoptera citricida. As a result the search for alternative rootstocks resistant to CTV and standing other constraints such as drough, alcalinity, salinity, phytophthora and nematods problems is now considered an urgent priority. Complementary genitors should be found in citrus germplasm to combine the desired traits particularly between Ponciros or trifoliate hybrids (citrange. citrumello) for resistances to pest and diseases and Citrus species for abiotic tolerances. The creation of somatic hybrids allows cumulating all dominant genes for tolerance to biotic and abiotic factors of the two parents, irrespective to their heterozygozity level. Moreover tetraploid level per se seems to irnprove toterances to salt and osmotic stress. Thus, the creation of new intergenetic and interspecific somatic hybrids has been included as one of the objectives in the 6th PCRD European Project 'ClBEWU' aiming to face the Mediterranean citrus rootstock challenge. New embryogenic callus lines to be used for somatic hybridization have been induced by INRAM (Morocco), lNRAT (Tunisia), Cukurova University (Turkey), IVIA (Spain) and CIRAD (France). Somatic hybridizations have been realized at CIRAD and IVIA with special emphasis in intergeneric (Citrus + Poncirus) combinations. Plants have been regenerated from 6 intergeneric and 1 interspecific combinations. Analysis of ploidy by flow cytometry and SSR markers studies are going on. The obtainment of interesting new tetraploid somatic hybrids has already been confirmed for 4 intergeneric (CIRAD: C. reshni + C35 citrange, C. sinensis + P. trifoliata; C. sinensis + C35 citrange; IVIA: C. macrophylla + Carrizo citrange) combinations and 1 interspecific combinations (IVIA: C. aurantium + C. taiwanica). Diploid cybrids with trifoliate hybrid nucleus and C. deliciosa or C. macrophylfa mitochondria have also been identified for 3 intergeneric combinations (CIR.AD: C. deliciosa + 4475 citrumello; C. deliciosa + C35 citrange; IVIA: C. macrophylla + Carrizo citrange). Methodological transfer to lNRAM (Morocco), INRAT (Tunisia) and Cukurova University (Turkey) has been done. (Texte intégral)