| The genus Rhodiola (Crassulaceae), a perennial herbaceous plant, consists of about 90 species all over the world, distributed mostly in the high cold region of the Northern Hemisphere. In China, there are 73 species, mainly growing in the Qinghai-Tibet Plateau.Rhodiola are one of important herbal medicine resources, the main effective chemical constituents from rhizomes of Rhodiola including salidroside, tyrosol, gallic acid and essential oils. They have long been used in the treatment of long-term illness and weakness due to infection in Tibet for over 1000 years. Recent pharmacological studies have shown that they have strong activities of anti-anoxia, anti-fatigue, anti-toxic, anti-radiation, anti-tumour, anti-aging, and active-oxygen scavenging. They are also used as a multipurpose medicinal plant with adaptogenic properties by effectively enhancing the body's ability to resist diseases and maintaining healthy. Recently, natural resources of Rhodiola have decreased remarkably owning to overexploitation for medicine and shrinkage of natural environment, so they have been considered as National Class One Endangered Species. Among them, Rhodiola crenulata is of significant medical value used by Tibetan hundreds of years ago, containing large amount of salidroside. It is mainly distributed in Tibet, Yunnan, Sichuan, and Qinghai, at high altitude of 2800-5600 m.In the present study, we used inter-simple sequence repeats ( ISSR ) to examine the genetic diversity of R. crenulata populations. We sampled 144 individuals from nine natural populations, of which seven from Yunnan and two from Tibet. Eleven ISSR primers were selected for PCR and produced 184 band loci, of which 180 ( P = 97.8 %) were polymorphic, across a total of 144 individuals. The average number of bands per prime was 15.3 and the size of the amplified DNA fragments ranged from 190 bp to 2600 bp. At species level, the gene diversity ( H ) was 0.297 and Shannon Index of diversity ( I ) is 0.4536. At populations level, the percentage of polymorphic loci ( P) is 30.98 % - 72.28 %, the gene diversity ( H ) was 0.1206 - 0.2218 and Shannon Index ( I ) is 0.1765 - 0.3383. The population from Shangrila, Yunnan demonstrated higher genetic diversity than the other populations. Compared with other species with the same traits, the pattern of genetic diversity in Rhodiola crenulata showed relatively higher level of genetic differentiation (GST were 0.404) and lower gene flow ( Nm were 0.7377 ). The coefficient of Gst of seven populations from Yunnan is 0.3743 and Nm is 0.8358, while as to the two populations from Tibet, GST is relatively lower compared with Yunnan, only 0.2312, and Nm is much higher, 1.6627. AMOVA analysis has indicated that 12.96 % of genetic variation existed among the different locations, 32.17 % of variation among populations within locations and 54.87 % among individuals within populations. The coefficient of Jaccard genetic similarity ranged from 0.241 to 0.967 among the nine populations, with the average of 0.443. The UPGMA dendrogram based on genetic distances among populations illustrated a strong relationship with geographical distribution. Nine populations were divided into three groups, with the two populations from Tibet clustering together, the two from Deqing, Yunnan grouping together and the rest from Lijiang and Shangrila, Yunnan forming a group. The results also indicated that ISSR is an effective approach to investigate the genetic diversity and genetic structure of R. crenulata.The chemical composition of essential oils from rhizomes of R.crenulata was analyzed by GC-MS qualitatively and quantitatively. 65 compounds were extracted from essential oils from eight populations in Tibet and Yunnan, among which 42 were identified. The main chemical constituents of R.crenulata included geraniol (14.78 - 55.11%),n-octanol (13.39 - 39.45%),2-methyl-3-buten-2-ol (0.82 - 24.15%), citronellol (2.18 - 8.86%),3-methyl-2-buten-1-ol (0.49 - 9.22%),mytenol (trace - 9.41%), linalool (1.41 - 4.05%) and so forth. The principal componen...
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