| Dipteronia Oliv., an endemic genus to China, belongs to the family Aceraceae. It only includes two species, namely D. dyeriana Henry and D. sinensis Oliv., which are respectively listed among Grade II and Grade III National Protected Rare and Endangered Plants. To better protect this germplasm resource, this paper has for the first time performed conservation genetic and molecular phylogeographical researches on the basis of large-scale collecting of plant materials of Dipteronia Oliv..Firstly, by referring to specimens, looking up related literature and visiting specialists, and through field surveys in 33 representative sites across nine provinces and cities such as Yunnan, Hubei and Chongqing, this paper has for the first time given a relatively comprehensive and timely report about Dipteronia Oliv.'s situation such as its growth status, habitats and artificial disturbances. All these have provided fundamental materials for the performance of related comprehensive researches.Secondly, a comparative study upon the genetic diversity and genetic differentiation of D. sinensis Oliv. and D. dyeriana Henry has been carried out by means of RAPD markers. 128 loci, with 119 of them polymorphic, have been detected in 226 individuals corresponding to 17 D. sinensis Oliv. populations by using 18 random primers. The proportion of polymorphic loci (PPB) is 92.97%, indicating that D. sinensis Oliv. has a relatively high level of genetic diversity. Shannon diversity index (0.5563), Net's gene diversity index (0.3864) and gene differentiation coefficient (GST=0.4470) together reveal a relatively high level of interpopulational genetic differentiation despite the existence of most genetic variation within populations. Results of AMOVA analysis show that D. sinensis Oliv.'s intrapopulational and interpopulational genetic variations account for 58.89% and 43.11% of the total amount of genetic variation respectively, which further supports the above-mentioned results. A deficiency in gene flow among D'. sinensis Oliv. populations has also been revealed (Nm=0.6685, Nm<1). Results of correlation analysis between interpopulational geographical distances (longitude, latitude and altitude) and interpopulational genetic distances show a remarkably significant positive correlation between genetic distancesand longitude differences (P<0.01). Results of clustering analysis and principal component analysis (PCA) also show a trend of correlation between each cluster group and geographical differences. By applying the same 18 primers to 45 individuals corresponding to 4 D. dyerlana Henry populations, RAPD analysis detects 103 loci, with 84 of them polymorphic, and reveals that its proportion of polymorphic loci (PPE) on the specific level is 81.55%. Results of AMOVA analysis show that D. dyeriana Henry's intrapopulational and interpopulational genetic variations account for 57.86% and 42.14% of the total amount of genetic variation respectively, which basically complies with the results of gene differentiation coefficient analysis (G.s7=0.4267). A limited gene flow among D. dyeriana Henry populations has also been revealed (Nm=0.6719, Nm<1). Results of correlation analysis show that there exists no significant correlation between interpopulational genetic distances and geographical isolation. By comparing the genetic diversity and genetic differentiation of D. dyeriana Henry and D. sinensis Oliv., it reveals that: (1) D. sinensis Oliv. has a higher level of genetic diversity than D. dyeriana Henry does, which follows the rule that the genetic diversity of cosmopolitan species is higher than that of stenochoric species; (2) both D. dyeriana Henry and D. sinensis Oliv. display a relatively high level of interpopulational genetic differentiation and a deficiency in gene flow among populations; (3) there exists a correlation between genetic and geographical distances on a large scale (D. sinensis Oliv.), but not on a small scale (D. dyeriana Henry), which may has something to do with the selection pressure exerted on species by their habitats...
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