VARIABILITY IN RDNA LOCI IN THE GENUS ORYZA DETECTED THROUGH FLUORESCENCE IN-SITU HYBRIDIZATION

The 17s-5.8s-25s ribosomal RNA gene (rDNA) loci in Oryza spp. were ide ntified by the fluorescence in-situ hybridization (FISH) method. The r DNA loci were located on one-to-three chromosomes (two-to-six sites) w ithin the eight diploid Oryza spp. One of the rDNA loci gave the weake st hybridization signal. This locus is reported for the first time in the genus Oryza. The chromosomes containing the rDNA loci were determi ned to be numbers 9, 10 and 11 in descending order of the copy number of rDNA. The application of image analysis methods, after slide prepar ation treatments (post-treatments), and the use of a thermal cycler, g reatly improved the reproducibility of the results. The evolutionary s ignificance of the variability of rDNA loci among the Oryza spp. is di scussed.