Résumé
In situ hybridization is an interesting technique for interspecific genome analysis particularly for polyploid species. In citrus, it should find applications to describe the genome structures of polyploid or aneuploid plants arising from sexual or somatic hybridization. In order to check the potential of these techniques in citrus, 3 diploid species of Citrus (C. medica, C. deliciosa, and C. maxima), Poncirus trifoliata, and Fortunella japonica have been studied by genomic in situ hybridization (GISH) and in situ hybridization with rDNA 18S-26S. GISH does not color the complete set of chromosomes. In most cases, only 5 pairs from 9 of the haploid set are colored. Moreover, the staining appears limiled to the extremity of chromosome and some central rDNA site. These results should be related to the small size of the nuclear citrus genome. The double staining of two intergeneric hybrids (C. deliciosa + P. trifoliata and C. deliciosa + F. japonica), with genomic DNA of each parent marked with different colors, shows that genomic differentiation between C. deliciosa on one hand and P. trifoliala or F . japonica on the other hand is sufficient to identify the stained chromosomes of each species. The differentiation of chromosomes at the infra-generic level, studied in a sexual hybrid between C. déliciosa and C. maxima, appears much more difficult. The number of chromosomes marked with rDNA probe (pTA71) per haploid set varies between 2 for C. medica to 6 for P. trifoliata. The perspective of applications and limits of these techniques foi polyploid or aneuploid citrus analysis are discussed. (Résumé d'auteur)