Comparative physical mapping of the 18S-5.8S-26S rDNA in three sorghum species

The physical locations of the 18S-5.8S-26S rDNA sequences were examined in three sorghum species by fluorescence in situ hybridization (FISH) using bi otin-labeled heterologous 18S-5.8S-26S rDNA probe (pTa71). Each 18S-5.8S-26 S rDNA locus occurred at two sites on the chromosomes in Sorghum bicolor (2 n = 20) and S. versicolor (2n = 10), but at four sites on the chromosomes o f S. halepense (2n = 40) and the tetraploid S. versicolor (2n = 20). Positi ons of the rDNA loci varied from the interstitial to terminal position amon g the four accessions of the three sorghum species. The rDNA data are usefu l for investigation of chromosome evolution and phylogeny. This study exclu ded S. versicolor as the possible progenitor of S. bicolor.