Abstract: The genetic diversity and the genetic structure of four in situ populations and one ex situ conservation population of riparian plant Distylium chinense in Hubei province was investigated using sequence-related amplified polymorphism (SRAP) molecular marker technique. A high level of genetic diversity at the species level was observed with the selected 7 SRAP primer combinations generating 46 discernible DNA fragments, of which 37 (80.43%) were polymorphic. The observed number of alleles (A), the mean effective number of alleles (A_e), Nei’s gene diversity index (H_p) and Shannon’s information index (I) was 2.00, 1.34, 0.215 9 and 0.350 9, respectively. Within populations, the genetic variation was found to be mainly caused by the variation within populations, accounting for 88.39% of the total genetic variation and only 11.61% among the populations. The gene flow of D.chinense between populations was 3.807 2, which was a relative high gene flow and could efficiently prevent gene drift and maintain current genetic structure. Based on unweighted pair-group method with arithmetic averages (UPGMA) dendrogram and principal coordinates analysis (PCA) diagram, the five populations studied may be divided into two groups. Most accessions along riversides in Hubei province including Letianxi, Xiangxi and Gaojiayan populations were found in one group, which was further divided into two subgroups that corresponded to the their geographic distance. Yanduhe and Three Gorges Botanical Garden populations were clustered into another group, showing that the accessions of ex situ conservation population had relatively high relatedness with those from Yanduhe population. The mean genetic diversity in ex situ conservation population was higher than those in situ populations. Hence, the ex situ conservation program of Three Gorges Botanical Garden was considered to be successful in preserving genetic diversity of D.chinense. Moreover, combining the analysis of the genetic diversity with available information on breeding system, status of natural habitat and evolutionary history, we also evaluated the current ex situ conservation program and proposed some effective strategies to further conserve the species. The results also suggested that SRAP molecular marker technique is valuable and reliable for evaluation of the genetic diversity estimation in D.chinense and this is the first report on the application of SRAP molecular marker technique in D.chinense.

Key words: Distylium chinense, SRAP markers, genetic diversity, genetic structure, conservation strategy