Abstract:

The cultivated rice has been differentiated and became not only two distinctly discriminative subspecies, i. e. O. sativa ssp. indica and O. sativa ssp. japonica but also many ecotypes of these two subspecies respectively. What is the variation law of the ITS1 and ITS2 sequences in varieties of a certain species with high biological diversity? Can the ITS region be a useful tool to study the phylogenetic relationships among these cultivars? Both of these are worthy of investigation. In this study, a comparative analysis of the rDNA internal transcribed spacers (ITS) entire sequences of 18 cultivars in Oryza sativa L. was carried out with O. rufipogon as outgroup. In the 18 cultivars, there were 9 O. sativa ssp. indica varieties, 6 typical O. sativa ssp. japonica, 2 O. sativa ssp. javanica and 1 upland rice. The result indicated that there were 23 variational loci which were 5.41% of entire bases and 8 informative loci which were 1.82% of entire bases in Oryza sativa. The length range of ITS sequence in O. sativa ssp. indica was from 425 to 430 bp; the percentage of G+C content varied from 74.25% to 75.59%. The length of ITS sequence in O. sativa ssp. japonica was 425 bp and the percentage of G+C content varied from 74.25% to 75.59%. The phylogenetic tree constructed on the basis of the ITS sequences showed that Oryza sativa was discriminated indica and japonica subspecies clearly, meanwhile, Oryza sativa ssp. javanica had closer relationships with O. sativa ssp. indica. The study shows that the sequences analysis of the internal transcribed spacer is a good tool to discriminate between subspecies of Oryza sativa and was significant in research the of Oryza sativa evolution.

Key words: Rice (Oryza sativa L.), Ribosome DNA (rDNA), Internal transcribed spacer (ITS), Phylogenetic tree