High Levels of Genetic Diversity within One Population of Rheum tanguti- cum on the Qinghai-Tibet Plateau have Implications for Germplasm Conservation

Rheum tanguticum, a source plant for the traditional Chinese medicine Dahuang (rhubarb), is an endangered species. In this study, we first assessed genetic diversity using 102 internal transcribed spacer (ITS) sequences cloned from one population of R. tanguticum on the Qinghai-Tibet Plateau. In total, 1773 polymorphic sites were identified, including 707 sites in the ITS1 region, 773 sites in the ITS2 region, and 293 sites on the 5.8S gene. Overall, transitions were the most common type of mutation and represented 77% of all base substitutions found within the ITS regions of R. tanguticum. We found that the average intra-specific genetic distance was 0.1260±0.0755 and ranged from 0 to 0.3618. Furthermore, a neighbor-joining phylogenetic tree constructed using these sequences strongly supported the conclusion that abundant intra-specific variation exists within the ITS regions of R. tanguticum. Interestingly, we found that eightyseven clones of R. tanguticum had high similarity to the ITS sequence of R. rhabarbarum and ten clones had high similarity to the ITS sequence of R. officinale; however, five clones of R. tanguticum had similarity to Fagopyrum esculentum. Therefore, we observed a significant amount of ITS sequence variation at both the intra-genomic and intra-specific levels in R. tanguticum. Based on these results, we suggest that in situ conservation is preferable for R. tanguticum protection.