Abstract: Chromosome localization of 45S rDNA was studied bymeans of fluorescence in situ hybridiza
tion ( FISH) on metaphase chromosomes of different p loidy Citrus grandis. NOR loci of different materials
showed obvious polymorphism and heterozygosity. There were four 45S rDNA loci in diploid, while there were
ten loci in tetrap loid t₁ and eight loci in tetrap loid t₂. Chromosomal location of rDNA loci included five types,
i1e. the telomeric region of the short arm, centromere to the short arm region, the centromeric region, centro
mere to the long arm region, the telomeric region of the long arm. Different materials had incomp lete same
rDNA loci types. The number of loci was not the same in different situations, the most were types of centro
mere to short arm region and centromeric region, next was the telomeric region of the short arm. There was a
variation in DNA among the homologous tetrap loids with the corresponding dip loid. Meanwhile, the citrus
chromosome slides used for F ISH and rDNA loci situation on chromosome, genetic variation analysis among the
homologous tetrap loids and dip loids, repeated sequence of chromosome in situ hybridization (CISH) for chro
mosome identification and species evolvementwere discussed.

Key words: Citrus grandis, Chromosome, Ploidy, Fluorescence in situ hybridization ( FISH)