Résumé
Citrus triploid hybrids can be recovered by 2x X 2x hybridisations as a consequence of 2n gamete formation. Two main meiotic processes are at the origin of such gametes, the first division restitution (FDR) and the second division restitution (SDR). These two mechanisms lead to very different gamete genetic structures. Particularly, the opposite feature of parental heterozygosity restitution (PHR) is observed in relation with the distance to the centromere. Without previous knowledge on centromere location, the determination of the restitution mechanism requires an analysis of the frequency of PHR within a large population with numerous codominant markers. With this method we determined that SDR is the mechanism involved in clementines and 'Fortune' mandarin. With SDR, PHR is a direct function of the distance of the considered locus to the centromere. Therefore the analysis of the evolution of PHR, within a linkage group (LG) allows mapping of the centromere position. Centromere has been located in the 9 LGs of the clementine genetic map by genotyping triploid hybrids with SSR and SNP markers. Analysis of the 2n gamete allelic configuration with loci close to the centromere can shed light on the restitution mechanism at the individual level and open the way for simplified study of this mechanism in a large range of genotypes. We are applying this approach to analyse the 2n gamete origin in several genotypes of mandarin and one genotype of sweet orange. (Texte intégral)