Analysis of genetic diversity in the endangered Hucho taimen from China

Hucho taimen are listed as endangered in China. The population size has declined recently, prompting an increase in the level of listing from grade three in 2002 to grade five in 2006. We analyzed the genetic diversity of wild populations using 17 microsatellite markers to establish a scientific basis for conservation of this species. We collected tissue samples from four populations in the Heilongjiang River basin: Huma River (HM), Hutou (HT), Haiqing (HQ), and Zhuaji (ZJ). A total of 21 loci were amplified, 18 of which were polymorphic. The number of alleles per locus ranged from 2 to 9 (mean: 4.1905). There were 13 highly polymorphic loci and 5 moderately polymorphic loci. Analysis of five genetic diversity parameters (Na, Ne, Ho, He, and PIC) suggested moderate levels of diversity within the populations. The populations were ranked HT > HQ > ZJ > HM, but the differences in diversity were not statistically significant (P > 0.05). A comparison of variation among all four populations suggested Hardy–Weinberg disequilibrium at 20% of the loci. Genetic differentiation (Fst) was 0.0644 and the gene flow among populations was estimated at 3.36 individuals per generation. The majority of diversity (93.88%) occurred among individuals within a population. In contrast, relatively little (6.12%) of the genetic diversity was distributed between the populations. An analysis of genetic differentiation and genetic distance between pairs of populations revealed that both parameters were higher in comparisons of the HM population to the HT, HQ, and ZJ populations than among the three latter populations. This suggests that the HM population has a distinct genetic structure. We hypothesize that habitat degradation and excessive fishing, not low genetic diversity, has caused the decline in H. taimen populations. However, this species should be protected from further declines in genetic diversity.     

Analysis of genetic diversity in the endangered Hucho taimen from China

Hucho taimen are listed as endangered in China. The population size has declined recently, prompting an increase in the level of listing from grade three in 2002 to grade five in 2006. We analyzed the genetic diversity of wild populations using 17 microsatellite markers to establish a scientific basis for conservation of this species. We collected tissue samples from four populations in the Heilongjiang River basin: Huma River (HM), Hutou (HT), Haiqing (HQ), and Zhuaji (ZJ). A total of 21 loci were amplified, 18 of which were polymorphic. The number of alleles per locus ranged from 2 to 9 (mean: 4.1905). There were 13 highly polymorphic loci and 5 moderately polymorphic loci. Analysis of five genetic diversity parameters (Na, Ne, Ho, He, and PIC) suggested moderate levels of diversity within the populations. The populations were ranked HT > HQ > ZJ > HM, but the differences in diversity were not statistically significant (P > 0.05). A comparison of variation among all four populations suggested Hardy–Weinberg disequilibrium at 20% of the loci. Genetic differentiation (Fst) was 0.0644 and the gene flow among populations was estimated at 3.36 individuals per generation. The majority of diversity (93.88%) occurred among individuals within a population. In contrast, relatively little (6.12%) of the genetic diversity was distributed between the populations. An analysis of genetic differentiation and genetic distance between pairs of populations revealed that both parameters were higher in comparisons of the HM population to the HT, HQ, and ZJ populations than among the three latter populations. This suggests that the HM population has a distinct genetic structure. We hypothesize that habitat degradation and excessive fishing, not low genetic diversity, has caused the decline in H. taimen populations. However, this species should be protected from further declines in genetic diversity.     

Development and Characterization of Fifteen Polymorphic Microsatellites for Extremely Endangered Salamander,Echinotriton chinhaiensis

Echinotriton chinhaiensis is a critically endangered salamander and its distribution is restricted to Ningbo, Zhejiang Province of China. In this study, we developed and characterized fifteen polymorphic microsatellite loci for E. ehinhaiensis from dinucleotide- and tetranucleotide- enriched library. The number of alleles ranges from 4 to 12 with an average of 7.27 alleles per locus. The observed and expected heterozygosities values were from 0.250 to 0.844 and 0.511 to 0.872 with an average value of 0.596 and 0.722; respectively. The polymorphic microsatellite loci described in this paper are useful in the further study on genetic diversity and gene flow, which would be helpful to formulate effective conservation strategies for the E. chinhaiensis.     

Microsatellite analysis of genetic diversity and population structure of Chinese mitten crab （Eriocheir sinensis）

Chinese mitten crab (Eriocheir sinensis) has higher commercial value as food source than any other species of Eriocheir in China.To evaluate the germplasm resources and characterize the genetic diversity and population structure of the crabs in different water systems,two stocks and two farming populations were assessed with 25 polymorphic microsallite loci available in public GenBank.Basic statistics showed that the average observed heterozygosity (Ho) amongst populations ranged from 0.5789 to 0.6824.However,a remarkable presence of inbreeding and heterozygote deficiencies were observed.To analyze population structure,pairwise FST coefficients explained only ～10.3% variability from the subdivision of mitten crab populations,the remaining variability stems from the subdivision within subpopulations.Although the four populations had slight differentiation,different allelic frequencies resulted in distinct population structures.Two stocks and one farming population were clustered together to the phylogenetic branch of Yangtze crab,with an approximate membership of 95%.Whereas,another fanning population was clustered singly to the phylogenetic branch of the Liaohe crab,with a membership of 97.1%.The tests for individual admixture showed that Yangtze crab had probably been contaminated with individuals from other water systems.Genetic relationships between populations also supported the conclusion that Yangtze crab and Liaohe crab had different gene pools in spite of the origins of the same species.     

Characterization of 12 polymorphic microsatellite markers in the Chinese tree shrew (Tupaia belangeri chinensis)

The Chinese tree shrew (Tupaia belangeri chinensis) is a small experimental animal with a close affinity to primates. This species has long been proposed to be an alternative experimental animal to primates in biomedical research. Despite decades of study, there is no pure breed for this animal, and the overall genetic diversity of wild tree shrews remains largely unknown. In order to obtain a set of genetic markers for evaluating the genetic diversity of tree shrew wild populations and tracing the lineages in inbreeding populations, we developed 12 polymorphic microsatellite markers from the genomic DNA of the tree shrew. An analysis of a wild population of 117 individuals collected from the suburb of Kunming, China, showed that these loci exhibited a highly expected heterozygosity (0.616). These 12 microsatellites were sufficient for individual identification and parentage analysis. The microsatellite markers developed in this study will be of use in evaluating genetic diversity and lineage tracing for the tree shrew.     

Genetic diversity of the endangered species Rosa rugosa Thunb. in China and implications for conservation strategies

Rosa rugosa Thunb. is one of the dominant and important shrub species in estuary dunes and shingle beaches of northern China. However, its area of distribution, the number of populations, and the size of each population have decreased rapidly in the past two decades because of habitat degradation and loss. Random amplified polymorphic DNA markers were used to determine the genetic diversity of four remaining large natural populations of R. rugosa and to discuss an effective conservation strategy for this endangered species in China. High genetic variations were detected in R. rugosa populations in China. The mean percentage of polymorphic loci （P%） within four local populations was 57.99%, with the P% of the total population being 75.30%. Mean Shannon＇s information index （H0） was 0.2826, whereas total Ho was 0.3513. The genetic differentiation among populations was 0.1878, which indicates that most genetic diversity occurs within populations. Population Tumenjiang （TMJ） showed the highest genetic diversity （P% = 66.27%; H0 = 0.3117） and contained two exclusive bands. Population Changshandao （CSD） showed higher genetic diversity （P% =59.04%; H0 = 0.3065）. Populations TMJ and CSD contained 95.33% and 99.33%, respectively, of loci with moderate to high frequency （P〉0.05） of the total population. These results indicate that populations TMJ and CSD should be given priority for in situ conservation and regarded as seed or propagule sources for ex situ conservation. The results of the present study also suggest that R. rugosa in China has become endangered as a result of human actions rather than genetic depression of populations; thus, human interference should be absolutely forbidden in R. rugosa habitats.     

The analysis of genetic diversity and differentiation of six Chinese cattle populations using microsatellite markers

A total of 321 individuals from six cattle populations of four species in a bovine subfamily in China were studied using 12 pairs of microsatellite markers. The genetic diversities within and between populations were calculated. The phylogenetic trees were constructed by （δμ）^2 and DA distances, and the divergence times between populations were estimated by （δμ）^2. Altogether, 144 microsatellite alleles were detected including 24 private alleles and nine shared alleles. Chinese Holstein had the largest number of private alleles （10）, whereas Bohai black and Buffalo had the smallest number of private alleles （2）. Chinese Holstein showed the highest genetic variability. Its observed number of alleles （Na）, mean effective number of alleles （MNA）, and mean heterozygosity （He） were 7.7500, 4.9722, and 0.7719, respectively, whereas, the Buffalo and Yak showed low genetic variability. In the phylogenetic trees, Luxi and Holstein grouped first, followed by Bohai and Minnan. Yak branched next and buffalo emerged as the most divergent population from other cattle populations. Luxi and Bohai were estimated to have diverged 0.039-0.105 million years ago （MYA）, however, buffalo and Holstein diverged 0.501-1.337 MYA. The divergence time of Yak versus Minnan, Holstein and buffalo was 0.136-0.363, 0.273-0.729, and 0.326-0.600 MYA, respectively.     

Genetic diversity and differentiation of masu salmon (Oncorhynchus masou masou) between and within cultured populations inferred from microsatellite DNA analysis

Masu salmon,Oncorhynchus masou masou,is one of the most valuable fishery species that has been introduced to China,though to date no studies on the genetic diversity and genetic relationship among hatchery populations has been performed with molecular markers.We undertook such a study and sampled 120 individuals from three hatchery stocks and analyzed 20 microsatellite loci.All loci were polymorphic and a total of 91 alleles were detected.A relatively low level of genetic diversity was revealed with effective number of allele of 3.1094,3.3299 and 3.1894 and expected heterozygosity of 0.6600,0.6648 and 0.6638 in the three stocks,respectively.Deviations from Hardy-Weinberg equilibrium were found due to heterozygote deficit.Accordingly,evidence of genetic bottlenecks were found in the three stocks.An individual assignment test demonstrated that 85% of individuals were correctly assigned into their original stocks.Pairwise Fst revealed that significant differentiation occurred between these three stocks.The results of the study indicated that disequilibrium of genetic structure and differentiation has occurred in all three stocks.This information collectively provides a basis for measures to avoid of loss of genetic diversity and introgression in Chinese aquaculture.     

栓皮栎天然群体SSR遗传多样性研究

利用微卫星(SSR)标记对我国4个省内的5个栓皮栎（Quercus variabilis Bl.）天然群体的遗传多样性进行了研究。16对SSR标记揭示了栓皮栎丰富的遗传多样性：等位基因数（A）平均8.4375个,有效等位基因数(Ne)平均为5.9512个,平均期望杂合度(He)0.8059,Nei多样性指数(h)为0.8041。栓皮栎自然分布区中心地带的群体具有较高的遗传多样性,而人为对森林的破坏将降低林木群体的遗传多样性。栓皮栎群体的变异主要来源于群体内,群体间分化较小,遗传分化系数仅为0.0455。此外,栓皮栎群体间的遗传距离与地理距离之间存在显著的正相关。这些遗传信息为栓皮栎遗传多样性的保护和利用提供了一定依据。Abstract: Genetic diversity of five Quercus variabilis natural populations in four provinces of China was studied with microsatellite (SSR) markers. A relatively high level of genetic diversity was detected in Q. variabilis species with 16 polymorphic microsatellite loci. Average number of alleles (A) and effective number of alleles (Ne) were 8.4375 and 5.9512 respectively. The mean expected heterozygosity (He) was 0.8059 and Nei diversity index (h) was 0.8041. Higher diversity was found with the populations from the central range of the species in contrast to those from peripheral areas and human activities might decrease the genetic diversity of populations. The majority of genetic variation occurred within populations, which could be concluded from the low coefficient of genetic differentiation (Fst=0.0455). In addition, significant correlation was found between geographical distance and genetic distance. All these results present a basis to the conservation and utilization of genetic diversity of Quercus variabilis.     

Isolation and Characterization of Nine Microsatellite Markers for Red-backed Ratsnake,Elaphe rufodorsata

The red-backed ratsnake(Elaphe rufodorsata) is widely distributed in East Asia, especially China. This species is a common snake in plain river network region. In the past several decades, E. rufodorsata has dramatically declined due to the effect of human activities and over hunting for traditional Chinese medicine. We developed nine species-specific microsatellite loci in 190 individuals collected from Huzhou, Zhejiang province in China. These markers revealed a high degree of genetic diversity(13–41 alleles per locus) and heterozygosity(H O ranged from 0.266 to 0.941, and H E ranged from 0.851 to 0.937). No locus exhibited significant deviations from Hardy–Weinberg equilibrium. There was no evidence of linkage disequilibrium among pairs of loci. These microsatellite markers were described in our study will be valuable tools for the long term management and population-level studies(e.g. the population structure, genetic diversity and variation, individual paternity and evolutionary history) of the species.     

湖羊、同羊12个同工酶座位的检测

Gene frequencies of Hu sheep and Tong sheep were obtained with “Random sampling in typical colonies of a central area“.of the 12 loci tested in Hu shpee.11 loci were polymorphic.Reliability of the estimated frequencies of 27 alleles reached 0.95 except for Po^F,Tf^A,Tfd,Hb-β^A and CAF which had reliabilities of 0.5222,0.7478,0.5222,0.6212 and 0.899,respectively,Of the 12 loci tested in Tong sheep,11 loci were polymorphic.Reliability of the estimated frequency of 25 alleles reached 0.95 except for Tf^A,Tf^E and CAF which had reliabilities of 0.931,0.6922 and 0.7924,respectively.The average heterozygosity(H) and average homozygosity(J) was computed and the J of the two sheep colonies was 0.6619 and 0.6448,respectively.Consistent with our conclusions based on genetic data,previous research divided the native sheep populations of East and South Central Asia into three group:the “mongolian group“ “south-Asian group“and “European group“ .Consequently,the degree of genetic similarity between populations and known groups would seem to provide a reliable means of determining the genetic relationships between populations and may reflect the true genetic origin of Hu sheep and Tong sheep in China.     

Examining the genetic diversity of Stipa grandis under various grazing pressures

The Stipa grandis steppe in the Inner Mongolia Autonomous Region occupies an area of 2798081 hm2. On the basis of the genetic variation, it was found that its adaptability to the environmental conditions under grazing pressure was significant. Using the Inter-Simple Sequence Repeat (ISSR) procedure, the changes to the genetic diversity of the Stipa grandis population under different grazing pressures were observed. Plant samples were collected from a series of grazing gradients of the Stipa grandis steppe in Dalinuoer National Nature Reserve in the Inner Mongolia (located at 116°38′–116°41′E and 43°25′–43°27′N.), which has the following vegetation types in abundance: Leymus chinensis is the constructive species; the dominant species include Stipa grandis, Cleistogenes squarrosa, and Artemisia frigida; the companion species is Potentilla acaulis and others. According to the grazing pressure, the following four grazing gradients were identified from the dwellings of the herdsmen to the enclosure site: (1) no grazing (CK enclosure site); (2) light grazing (LG); (3) moderate grazing (MG); (4) heavy grazing (HG). Young leaves of each Stipa grandis were collected during the growing season. The results showed that the Stipa grandis showed abundant genetic diversity despite the fact that certain polymorphic loci were lost; at the same time, new polymorphic loci emerged when grazing pressure increased; a total of 10 primers were used, and 74 bands were produced in total, of which 65 bands were polymorphic; the total percentage of polymorphism was 89%; the percentage of polymorphic loci of the Stipa grandis population decreased with the increase of grazing pressure; the percentage of polymorphic loci was 62.2% in the no-grazing (CK) population, 64.9% in the light-grazing (LG) population, 58.1% in the moderate-grazing (MG) population, and 56.8% in the heavy-grazing (HG) population; the genetic diversity of the population in the descending order using the Shannon's information index is as follows: (1) light grazing (0.3486); (2) no grazing (0.3339); (3) moderate grazing (0.3249); (4) heavy grazing (0.2735) with the same distributional pattern as the Nei's genetic diversity index. The test showed the following: As the grazing pressures increased, the change of genetic diversity decreased; the genetic differentiation coefficient among the population (Gst) was 0.1984, which showed the presence of small partial genetic diversity (19.8%) among populations; gene flow (Nm*) between primers varied from 0.9806 to 3.4463, and the mean gene flow (Nm*) was 2.0202; the UPGMA cluster figure that was constructed on the basis of the genetic distance matrix showed four populations that became genetically closer at each step: (1) The first group was the moderate-grazing (MG) population and the heavy- grazing (HG) population; (2) The second group consisted of the no-grazing (CK) population and the light-grazing (LG) population; (3) The two groups gathered together.     

RAPD analysis of natural populations of Acanthopanax brachypus

Random amplified Polymorphic DNA(RAPD) analysis is a new technology of molecular marking which has proved very powerful in detecting genetic diversity at the level of population.The genomic DNAs used in our experiment were extracted from fresh leaves taken from 59 individuals sampled from three natural populations in Yan an,Shanxi Province.Through more than 2,000 PCRs,deep-going RAPD analysis was carried out on DNA samples from 49 inviduals.The percentage of polymorphic RAPD loci found in these three populations were respectively 27.2%,18.6% and 5.4%;the average genetic distances within population,0.055,0.026 and 0.008;the average genetic distances between populations (I-II),(I-III) and (II-III),0.105,0.096 and 0.060.The genetic diversity of A.brachypus within and between populations was found,for the first time,to be rather poor,thus revealing innate factors as the cause contributing to its endangered status.In addition,our work also provides basic materials for elucidating the underlying cause of its endangerment and for its protection biology.     

Genetic structure of Himalayan marmot (Marmota himalayana) population alongside the Qinghai–Tibet Railway

In order to verify the effect of social behavior and geographical isolation on the genetic structure of the Himalayan marmot (Marmota himalayana) population, we examined the genetic diversity of Himalayan marmots alongside the Qinghai–Tibet Railway using microsatellite markers. Eight microsatellite loci were used to examine 120 animals of 4 populations: Ulan (U), Delhi (D), Tuotuohe (T) and Ando (A). The results show that: (1) Himalayan marmots alongside the Qinghai–Tibet Railway are highly genetically diversified. The allele number (Na), effective allele number (Ne), observed heterozygosity (Ho), Nei’s expected heterozygosity (He) and polymorphism information content (PIC) of the total Himalayan marmot population were 4.75, 3.0332, 0.6990, 0.6672, 0.6102, respectively. (2) Himalayan marmots may be able to avoid inbreeding by a mechanism that will prevent the genetic diversity reduction caused by their social lifestyle. Heterozygote excess was observed at most loci. The inbreeding coefficients within the subpopulation (F_IS), in the total population (F_IT), the differentiation index of population (F_ST), and the gene flow (Nm) were ?0.2265, ?0.0477, 0.1458, and 1.4646, respectively. (3) The genetic differentiation of the Himalayan marmot population was in accordance with Wright’s “isolation by distance” theory. The Mantel test indicates that the correlation between genetic distance and geographic distance was significant (P < 0.05, r = 0.698). (4) Each of the four geographical populations had moderate differentiation. Both geographic distance and isolation could affect the population genetic structure of the Himalayan marmot. The maximum gene flow (3.5915), the smallest genetic differentiation index (0.0651), the lowest genetic distance (0.0700) and the highest genetic identity (0.9526) were all between the Ulan population and Delhi populations. (5) The cluster analysis, based on Nei’s standard genetic distance, showed that the populations of Delhi and Ulan were first merged in a cluster, and then Tuotuohe population was merged in the clustering. The Ando population was the last element in the clustering.     

Genetic structure of Himalayan marmot (Marmota himalayana) population alongside the Qinghai–Tibet Railway

In order to verify the effect of social behavior and geographical isolation on the genetic structure of the Himalayan marmot (Marmota himalayana) population, we examined the genetic diversity of Himalayan marmots alongside the Qinghai–Tibet Railway using microsatellite markers. Eight microsatellite loci were used to examine 120 animals of 4 populations: Ulan (U), Delhi (D), Tuotuohe (T) and Ando (A). The results show that: (1) Himalayan marmots alongside the Qinghai–Tibet Railway are highly genetically diversified. The allele number (Na), effective allele number (Ne), observed heterozygosity (Ho), Nei’s expected heterozygosity (He) and polymorphism information content (PIC) of the total Himalayan marmot population were 4.75, 3.0332, 0.6990, 0.6672, 0.6102, respectively. (2) Himalayan marmots may be able to avoid inbreeding by a mechanism that will prevent the genetic diversity reduction caused by their social lifestyle. Heterozygote excess was observed at most loci. The inbreeding coefficients within the subpopulation (F_IS), in the total population (F_IT), the differentiation index of population (F_ST), and the gene flow (Nm) were ?0.2265, ?0.0477, 0.1458, and 1.4646, respectively. (3) The genetic differentiation of the Himalayan marmot population was in accordance with Wright’s “isolation by distance” theory. The Mantel test indicates that the correlation between genetic distance and geographic distance was significant (P < 0.05, r = 0.698). (4) Each of the four geographical populations had moderate differentiation. Both geographic distance and isolation could affect the population genetic structure of the Himalayan marmot. The maximum gene flow (3.5915), the smallest genetic differentiation index (0.0651), the lowest genetic distance (0.0700) and the highest genetic identity (0.9526) were all between the Ulan population and Delhi populations. (5) The cluster analysis, based on Nei’s standard genetic distance, showed that the populations of Delhi and Ulan were first merged in a cluster, and then Tuotuohe population was merged in the clustering. The Ando population was the last element in the clustering.     

Examining the genetic diversity of Stipa grandis under various grazing pressures

The Stipa grandis steppe in the Inner Mongolia Autonomous Region occupies an area of 2798081 hm2. On the basis of the genetic variation, it was found that its adaptability to the environmental conditions under grazing pressure was significant. Using the Inter-Simple Sequence Repeat (ISSR) procedure, the changes to the genetic diversity of the Stipa grandis population under different grazing pressures were observed. Plant samples were collected from a series of grazing gradients of the Stipa grandis steppe in Dalinuoer National Nature Reserve in the Inner Mongolia (located at 116°38′–116°41′E and 43°25′–43°27′N.), which has the following vegetation types in abundance: Leymus chinensis is the constructive species; the dominant species include Stipa grandis, Cleistogenes squarrosa, and Artemisia frigida; the companion species is Potentilla acaulis and others. According to the grazing pressure, the following four grazing gradients were identified from the dwellings of the herdsmen to the enclosure site: (1) no grazing (CK enclosure site); (2) light grazing (LG); (3) moderate grazing (MG); (4) heavy grazing (HG). Young leaves of each Stipa grandis were collected during the growing season. The results showed that the Stipa grandis showed abundant genetic diversity despite the fact that certain polymorphic loci were lost; at the same time, new polymorphic loci emerged when grazing pressure increased; a total of 10 primers were used, and 74 bands were produced in total, of which 65 bands were polymorphic; the total percentage of polymorphism was 89%; the percentage of polymorphic loci of the Stipa grandis population decreased with the increase of grazing pressure; the percentage of polymorphic loci was 62.2% in the no-grazing (CK) population, 64.9% in the light-grazing (LG) population, 58.1% in the moderate-grazing (MG) population, and 56.8% in the heavy-grazing (HG) population; the genetic diversity of the population in the descending order using the Shannon's information index is as follows: (1) light grazing (0.3486); (2) no grazing (0.3339); (3) moderate grazing (0.3249); (4) heavy grazing (0.2735) with the same distributional pattern as the Nei's genetic diversity index. The test showed the following: As the grazing pressures increased, the change of genetic diversity decreased; the genetic differentiation coefficient among the population (Gst) was 0.1984, which showed the presence of small partial genetic diversity (19.8%) among populations; gene flow (Nm*) between primers varied from 0.9806 to 3.4463, and the mean gene flow (Nm*) was 2.0202; the UPGMA cluster figure that was constructed on the basis of the genetic distance matrix showed four populations that became genetically closer at each step: (1) The first group was the moderate-grazing (MG) population and the heavy- grazing (HG) population; (2) The second group consisted of the no-grazing (CK) population and the light-grazing (LG) population; (3) The two groups gathered together.     

Temporal changes in SSR allelic diversity of major rice cultivars in China

Forty simple sequence repeats （SSRs） were used to assess the changes of diversity in 310 major Chinese rice cultivars grown during the 1950s-1990s. Of the 40 SSR loci, 39 were polymorphic. A total of 221 alleles were detected with an average of 5.7 alleles per locus （Na）. The Nei＇s genetic diversity index （He） varied drastically among the loci （0.207 to 0.874, mean 0.625）. Comparing the temporal changes in Na and He, the cultivars from the 1950s had more alleles and higher He scores than the cultivars from the other four decades. Analysis of molecular variance （AMOVA） indicated that the genetic differentiation among the five decades was not significant in the whole set, but significant within indica and japonica. More changes among the decades were revealed in indica cultivars than in japonica cultivars. Some alleles had been lost in current rice cultivars in the 1990s, occurring more frequently in indica. These results suggest that more elite alien genetic resources should be explored to widen the genetic backgrounds of rice cultivars currently grown in China.     

Glacial Refugia of Ginkgo biloba and Human Impact on Its Genetic Diversity： Evidence from Chloroplast DNA

Variations in the trnK region of chloroplast DNA were investigated in the present study using polymerase chain reactionrestriction fragment length polymorphism to detect the genetic structure and to infer the possible glacial refugia of Ginkgo biloba L. in China. In total, 220 individuals from 12 populations in China and three populations outside China were analyzed, representing the largest number of populations studied by molecular markers to date. Nineteen haplotypes were produced and haplotype A was found in all populations. Populations in south-western China, including WC, JF, PX, and SP, contained 14 of the 19 haplotypes and their genetic diversity ranged from 0.771 4 to 0.867 6. The TM population from China also showed a high genetic diversity （H = 0.848 5）. Most of the genetic variation existed within populations and the differentiation among populations was low （GsT = 0.2）. According to haplotype distribution and the historical record, we suggest that populations of G. biloba have been subjected to extensive human impact, which has compounded our attempt to infer glacial refugia for Ginkgo. Nevertheless, the present results suggest that the center of genetic diversity of Ginkgo is mainly in south-western China and in situ conservation is needed to protect and preserve the genetic resources.     

Low genetic diversity and high genetic differentiation in the critically endangered Omphalogramma souliei （Primulaceae）： implications for its conservation

Omphalogramma souliei Franch. is an endangered perennial herb only distributed in alpine areas of SW China. ISSR markers were applied to determine the genetic variation and genetic structure of 60 individuals of three populations of O. souliei in NW Yunnan, China. The genetic diversity at the species level is low with P=42.5% （percentage of polymorphic bands） and Hsp=0.1762 （total genetic diversity）. However, a high level of genetic differentiation among populations was detected based on different measures （Nei＇s genetic diversity analysis： Gst=0.6038; AMOVA analysis： Fst=0.6797）. Low level of genetic diversity within populations and significant genetic differentiation among populations might be due to the mixed mating system in which xenogamy predominated and autogamy played an assistant role in O. souliei. The genetic drift due to small population size and limited current gene flow also resulted in significant genetic differentiation. The assessment of genetic variation and differentiation of the endangered species provides important information for conservation on a genetic basis. Conservation strategies for this rare endemic species are proposed.