Genetic Diversity And Population Structure Study Of Ntural Pteroceltis Tatarinowii Populations

Pteroceltis is a monotypic genus belonging to Ulmaceae and is endemic to China. As an ancient Tertiary relic plant, P. tatarinowii was recorded to distribute continuously across temperate to sub-tropical limestone region. In view of its importance in classification and high economic value, P. tatarinowii was listed as an endangered species and of the third nationally protected plant in Chinese Plant Red Data Book-Rare and Endangered Plants. However, its geographical range is shrinking and population fragmentation is becoming increasingly serious at present because of the degradation of biotope and extensive deforestation. In this study, two molecular markers containing fluorescently labeled AFLP and SRAP were used to assess the amount of genetic diversity and the magnitude of its genetic divergence of P. tatarinowii, which will contribute to provide the scientific basis for valuation, collection and protection of P. tatarinowii. The results are as follows:Genetic diversity : A total of 159 bands ranging from 50 to 500 were identified by AFLP, among which 142 were regarded as polymorphic. Eight SRAP primer combinations produced 125 bands across all individuals, of which 113 were polymorphic. At species level, expected heterozygosity(HE) was 0.2239 as estimated by AFLP and 0.2544 by SRAP, Shannon′s information index(IS) was 0.3550/0.3941, the percentage of polymorphic loci(PPL) was 89.31/90.40. Both of the two molecular markers are suiTab. to test the genetic diversity of P. tatarinowii.Genetic differentiation and genetic structure of populations: Coefficient of differentiation Gst was 0.2073 and 0.2607, implying 20.73% and 26.07% variations existed among populations by AFLP and SRAP respectively. Relationship among populations was further illustrated by a NJ dendrogram for AFLP based on Nei′s genetic distance, while population clustering with UPGMA for SRAP based on Nei′s genetic distance. Three populations which were collected from Beijing and Henan were clustered together in both NJ and UPGMA analysis, the same situation was also existed in three populations which were collected from Shandong, Anhui and Hubei. Slightly difference happened to the clustering of the remaining five populations which were collected from Jiangsu, Jiangxi, Hunan, Guizhou and Guangxi. Coherent trend by different markers ensured the reliability. Mantel test revealed no significant relationship between genetic distance and geographical distance(r = 0.28, p= 0.96 for AFLP; r= 0.33, p = 0.99 by SRAP). In the STRUCTURE analysis of AFLP data, the highest K was obtained when K = 2, indicating the existence of two genetic groups A and B. In group A, there contained six populations which were collected from Beijing, Henan, Shandong, Anhui and Hubei. The remainder populations which were collected from Jiangsu, Jiangxi, Hunan, Guizhou and Guangxi were placed in group B. This result is consistent with UPGMA cluster analysis. Relationship among individuals analyzed by PCoA show that only 13.99% of the total variance was explained by the first three components. From the 3D plot, four groups can be captured roughly despite of the overlapping of some individuals and this result also corresponded with UPGMA cluster analysis.Conservation consideration: The result in the present study demonstrated P. tatarinowii retained a high level genetic diversity and moderate level of genetic differentiation. Since the moderate genetic differentiation revealed and considering the special habitat of this species, in situ conservation is first recommended. Secondly, population which was collected from Guizhou was genetically distant from other populations and so should be paid enough attention for ex situ conservation. This will ensure the maintenance of most species′ genetic variance. Finally, small plant populations are more prone to extinction due to the loss of genetic variation through random genetic drift, increased selfing, and mating among related individuals. From our investigation, populations which were collected from Guizhou and Hunan relatively have low genetic diversity as a result of small population size, so the two populations should be taken into account both in situ and ex situ conservation.