Phylogenetic Relationships of Sorghum and Related Species Inferred from Sequence Analysis of the nrDNA ITS Region

Analysis of phylogenetic and evolution in six species of Sorghum was based on internal transcribed spacer (ITS) sequences in nuclear ribosomal DNA. Results showed that the length of the ITS regions among the six species ranged from 588 to 589 bp and the contents of G + C in ITS (ITS1+5.8S+ITS2) regions ranged from 60.27 to 61.05%; the length of ITS1 ranged from 207 to 208 bp and the contents of G + C in the ITS1 regions ranged from 53.91 to 61.54%. The length of the 5.8S rDNA and ITS2 regions in the six species was 164 and 217 bp respectively, and the contents of G + C ranged from 56.10 to 58.54% in the 5.8S rDNA region and 66.36 to 67.28% in the ITS2 region. Among regions of ITS, ITS1, ITS2, and 5.8S, the best sequence for genetic relationship analysis in the six species was the ITS region. On the basis of the Jaccard coefficient and phylogentic tree, S. sp. was more related to S. propinguum than to other species. This was consistent with the fact that S. sp. is derived from S. propinguum. From the phylogenetic tree based on ITS1, S. halepense, silk sorghum and S. sudanense, are identical in the ITS1 sequence, whereas the phylogenetic tree based one shows that S. sudanense has a closer genetic association with S. almum rather than with S. halepense and silk sorghum.