Natural Hybridization Study Between Two Species Of Nitraria In Inner Mongolia By Molecular Markers

Nitraria L. is an old small genus of Zygophyllaceae. In its natural distribution area of Western Inner Mongolia, extensive overlapping distributions of Nitraria roborowskii and N.tangutorum are found, many plants showed continuous transitions of shape variations. Its category can not be defined by morphology independently. It is speculated that the continuous transitions may be caused by the extensive hybridization or strong introgression between Nitraria roborowskii and N.tangutorum. The study on introgressive hybridization between two species of Nitraria will not only lead to a deeper understanding of the mechanisms of formation and evolution of species, but also play significant impact on probe of species differentiation process, the conservation and utilization of germplasm resources of Nitraria. In this paper, ISSR molecular labeling technique, the sequence comparison of the internal transcribed spacer (ITS) regions of nuclear ribosomal and trnL-F intergenic spacer region of the chloroplast DNA from N.roborowskii, N.tangutorum and the suspected hybrids were performed. The main results are as follows: 1. In this paper, orthogonal design was used to obtain optimum scheme on reaction system for ISSR of species in Nitraria L.2. Eleven ISSR random primers amplified a total of 95 DNA loci, percentage of polymorphic loci is 96.84%. Shannon's information index of hybrids was 0.4633±0.2067. The value was higher than N.roborowskii (0.3576±0.2762), and the value of N.roborowskii was higher than that of N.tangutorum (0.3477±0.2925). High level Nm suggested a sufficient genetic exchange and low genetic divergence among populations. The mean value of heterozygosity between populations was higher than that found within populations. Above show that hybridizations exist between N.roborowskii and N.tangutorum.3. The three populations of Nitraria had high genetic polymorphism. Nei's gene diversity index (H) and Shannon index (I) in population level, the sequence all were:Hybrids> Nitraria roborowiskii> N.tangutorum. Percentage of polymorphic loci follow the same sequence.4. The cluster analysis on all populations demonstrated that the branch of five populations of the hybrids were clustered together with the branch of six populations of Nitraria roborowiskii firstly, and then with the populations of N.tangutorum. It indicated that kinships were nearer between the hybrids and Nitraria roborowiskii.5. The sequence comparison of the trnL-F intergenic spacer region of the chloroplast DNA from N.roborowskii, N.tangutorum and the hybrids was performed. The 73.3 percent of the locus were the same between hybrids and N.roborowskii,26.7 percent were the same between hybrids and N.tangutorum.6. The sequence comparison of the internal transcribed spacer (ITS) regions of nuclear ribosomal from N.roborowskii, N.tangutorum and the hybrids was conducted. The 37.5 percent of the locus had two different ITS sequence copies in each individual of hybrids. The 25 percent were the same between hybrids and N.roborowskii and the 37.5 percent were the same between hybrids and N.tangutorum. The results suggested that all intermediate individuals were the introgressive hybrids between N.roborowskii and N.tangutorum.