| Styrax obassia Sieb.et Zucc is an industrially important landscape tree that produces storax, a resin with pharmacological properties. Previous studies on S. obassia have only focused on extraction, seedling characteristics and cultivation techniques. The genetic diversity and relationships of S. obassia germplasm remain unknown. Evaluation of the diversity and patterns of genetic variation of S. obassia is needed to assist protection and utilization of this plant resource. Because human disturbance has caused a sharp decline in natural populations of S. obassia, the adoption of effective conservation strategy for this species is also urgently needed. In the present study, AFLP markers were used to characterize the genetic diversity and relationships of 76 individuals from five different populations of S. obassia. To provide basic recommendations for the development of conservation strategies for natural S. obassia resources, we evaluated genetic diversity at population and species levels, examined genetic differentiation among populations, and identified individuals and populations characterized by high polymorphism levels.1.Genetic diversity: Eight AFLP primers selected from 64 primers were used to generate 1343 discernible DNA bands, of which 1338(99.60%) were polymorphic. High genetic diversitywas revealed at the species level(number of different alleles Na= 1.9960, number of effective alleles Ne=1.2782, Nei's gene diversity H = 0.1764, Shannon's information index I = 0.2883). 218 specific bands including 1 absent band were amplified from 76 individuals, which account for 16.29 % of total polymorphic bands. Genetic similarity coefficient of 76 individuals changed from 0.4033 to 0.7492 with the average was 0.5844. At a similarity coefficient threshold of 0.55, all individuals were divided into two clusters, and most individuals from the same population grouped together in a single cluster. At the population level, percentage ofpolymorphic bands(PPB) per population ranged from 42.3% to 76.6%, with an average of 57.2%. Assuming Hardye Weinberg equilibrium, Nei's gene diversity(H) was estimated to be 0.1451. The value of Shannon's information index(I) ranged from 0.1932 to 0.2659, with an average of 0.2289. The order of polymorphism percentage from high to low was: KY3 >HC > KY1>JX >LS.2. Genetic relationship: Among populations, Nei's unbiased genetic identity(In) varied from 0.9520(between JX and LS) to 0.9831(between KY1 and KY3), with an average of 0.9674. The smallest genetic distance(D = 0.0171) was detected between population KY1 and KY3, and the largest genetic distance(D = 0.0510) was founded between population LS and JX. As shown in the dendrogram, relationships among the five populations were analyzed based on Nei's genetic distance(D) using UPGMA clustering method. Populations KY1 and KY2 were first grouped into a cluster, then gathered together with population HC, and finally with populations JX and LS. The Mantel test revealed no significant correlation between pairwise genetic distance and geographical distance among all the populations(r = 0.4727, p = 0.9106).3. Genetic structure: In the present study, a high level of genetic differentiation among population was detected(Gst=0.1576, ?PT=0.1152), and Nm was estimated to be 3.1404, which suggested the existence of a strong gene exchange among these five populations.4.Construction of the core collection of S. obassia: The core collection of ancient ginkgo trees with 23 individuals account for 30% of original collection. The results of t-test showed that no significant different was found in genetic diversity indexes between the core collection and original collection. These results demonstrated that the core collection could stand for original collection excellently. The finger-print of S. obassia was built by AFLP result.On the basis of these results, a strategy for the conservation of S. obassia germplasm was proposed. |
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