Studies On Molecular Systematics And Genetic Diversity Of Genus Nitraria L.

The genus Nitraria L. consists of 12 species, distributed in desert areas of Asia, European, African and Australian. There are 7 species in China and 5 species in Gansu province. In China, species of Nitraria mainly distributes in northwestern desert and form the dominant species in desert and semidesert vegetation. They possess the characteristics of toleration of dry and cold, salt and base, wind blow and sand bury, they also grow fast and reproduce easily, so they are excellent pioneer for revegetating of desert. In this paper, the molecular systematics, genetic diversity, drought resistant physiology of the species of Nitraria were studied, based on the 5 species of Nitraria distributed in Hexi Corridor. The results were as follows.1. The plastid gene rbcL, trnL-F and their combination for 5 species of Nitraria L. and 43 taxa representative of several putatively related families were studied using maximum parsimony analysis. A far distance was detected between Nitraria and other genera of Zygophyllaceae, but Nitraria had close affinity with Peganum. In trnL-F tree, Nitraria appeared as sister group to Sapindaceae of Sapindales. In rbcL tree, trnL-F and rbcL combined tree, Nitraria and Sapindaceae were paraphyletic with high bootstrap value (99-100%). The phylogenetic analysis indicated that Nitraria should be separated from Zygophyllaceae and constituted a separate family, Nitrariaceae. The results also demonstrated that Nitraria had close affinity with Peganum, but in view of many differences in morphology, biochemistry, embryology between them, Nitraria and Peganum should probably constitute separate families, Nitrariaceae and Peganaceae. Meanwhile, in ordor status, molecular data supported to place Nitrariaceae in Order Sapindales.2. The sequences of the ITS region (including ITS-1, 5.8S rDNA and ITS-2) of nuclear ribosomal DNA from 5 species of the genus Nitraria L. in Gansu were determined. The result showed that the size of the ITS region of Nitraria was from 630 to 674 bp. The varieties of ITS region had classification significations in Nitraria. On the basis of phylogenetic analysis of nucleotide sequences, the species of Nitraria in Gansu could be devided into tree groups, group I consisted of N. sibirica; group II consisted of N. sphaerocarpa; group III includeed N. praevisa, N. roborowskii and N. tangutorum.