Abstract: The materials of experiment were natural triploids, natural tetraploids selected in seeds and diploids of Citrus sinensis Osbeck. 'Hongjiangcheng'. Making use of the technique of 45S rDNA-FISH, the FISH karyotypes of these materials were studied and the results were analysized. Three hybridized signals were detected on NORs(nuclear organization region) on chromosomes number 1 and all regions of satellite of chromosome number 8 in the mitotic metaphase. Four hybridized signals located on the mitotic metaphase chromosomes of triploid. One signal was detected on NOR of chromosome number 3, and the other three were same as diploid. There were six hybridized signals on the mitotic metaphase chromosomes of tetraploid, and these signals were same as diploid. And same hybridized signals were detected on mitotic interphase. According to the results, the formation of triploids should be relative to 2n female gametes with recombination of foreign genes. Tetraploids should be relative to the chromosome doubling of nucellus cells, and a few chromosomes breakage and translocation were found.

Key words: Citrus sinensis Osbeck., polyploid, fluorescence in situ hybridization, signal