中国石榴栽培群体遗传多样性的荧光AFLP分析

以中国山东、安徽、陕西、河南、云南和新疆6个栽培石榴群体的85个品种类型为试材,利用荧光标记AFLP对中国石榴群体遗传多样性进行了研究。结果表明：8对引物组合在种级水平扩增的多态性位点数范围从135～185个不等,平均为158.25个,多态位点百分比范围为62.5%～86.11%,平均为73.26%,说明中国石榴品种遗传多样性较为丰富;石榴品种种级水平遗传多样性大于群体水平,6个群体的遗传多样性依次为河南群体〉新疆群体〉陕西群体〉安徽群体〉山东群体〉云南群体,并且具有显著性差异;群体间的遗传分化系数GST为0.2018,说明石榴遗传变异主要存在群体内,群体间的遗传变异占总变异的20.18%,根据基因分化系数,测得的基因流Nm为1.9027,说明中国石榴群体间存在适当的基因交流;UPGMA聚类分析结果表明,同一群体的大部分品种都聚在一起,但同时存在部分基因交流。所有遗传参数表明,中国石榴栽培品种遗传多样性较为丰富,其中河南群体遗传多样性显著高于其他群体,在中国石榴品种选育中具有更为广阔的应用前景。     

Genetic diversity of the endangered Chinese endemic herb Primulina tabacum (Gesneriaceae) revealed by amplified fragment length polymorphism (AFLP)

Primulina tabacum Hance, is a critically endangered perennial endemic to limestone area in South China. Genetic variability within and among four extant populations of this species was assessed using AFLP markers. We expected a low genetic diversity level of this narrowly distributed species, but our results revealed that a high level of genetic diversity remains, both at population level (55.5% of markers polymorphic, H _E = 0.220, I _S = 0.321), and at species level (P = 85.6% of markers polymorphic, H _E = 0.339, I _S = 0.495), probably resulting from its refugial history and/or breeding system. High levels of genetic differentiation among populations was apparent based on Nei’s genetic diversity analysis (G _st=0.350). The restricted gene flow between populations is a potential reason for the high genetic differentiation. The population genetic diversity of P. tabacum revealed here has clear implications for conservation and management. To maintain present levels of genetic diversity, in situ conservation of all populations is necessary.     

Cryptic population genetic structure: the number of inferred clusters depends on sample size

Clustering methods have been used extensively to unravel cryptic population genetic structure. We investigated the effect of the number of individuals sampled in each location on the resulting number of clusters. Our study was motivated by recent results in Arabidopsis thaliana: studies in which more than one individual was sampled per location apparently have led to a much higher number of clusters than studies where only one individual was sampled in each location, as is generally done in this species. We show, using computer simulations and microsatellite data in A. thaliana, that the number of sampled individuals indeed has a strong impact on the number of resulting clusters. This effect is smaller if the sampled populations have a hierarchical structure. In most cases, sampling 5–10 individuals per population should be enough. The results argue for abandoning the concept of ‘accessions’ in partially selfing organisms.     

Estimating genetic diversity of Arabidopsis thaliana ecotypes with amplified fragment length polymorphisms (AFLP)

The extensive natural variation of Arabidopsis thaliana ecotypes is being increasingly exploited as a source of variants of genes which control (agronomically) important traits. We have subjected 19 different Arabidopsis thaliana ecotypes to an analysis using the anplified fragment length polymorphism (AFLP) technique in order to estimate their genetic diversity. The genetic diversity was estimated applying the method of Nei and Li (1979) and a modified version of it and using 471 informative polymorphisms. The data obtained revealed that within this small set of ecotypes a group of three ecotypes and a further single ecotype exhibit considerable genetic diversity in comparison to the others. These ecotypes clustered at positions significantly separated from the bulk of the ecotypes in the generated similarity plots. The analysis demonstrated the usefulness of the AFLP method for determinating intraspecies genetic diversity as exemplified with Arabidopsis thaliana ecotypes. Results are discussed and compared with data obtained with other methods. Received: 18 June 1999 / Accepted: 28 July 1999     

Genetic consequence of restricted habitat and population decline in endangered Isoetes sinensis (Isoetaceae)

BACKGROUND AND AIMS: Isoetes sinensis (Isoeteaceae) is a critically endangered aquatic quillwort in eastern China. Rapid decline of extant population size and local population extinction have occurred in recent years and have raised great concerns among conservationists. METHODS: Amplified fragment length polymorphisms (AFLPs) were used to investigate the genetic variation and population structure of seven extant populations of the species. KEY RESULTS: Eight primer combinations produced a total of 343 unambiguous bands of which 210 (61.2 %) were polymorphic. Isoetes sinensis exhibited a high level of intra-population genetic diversity (H(E) = 0.118; hs = 0.147; I = 0.192; P = 35.2 %). The genetic variation within each of the populations was not positively correlated with their size, suggesting recent population decline, which is well in accordance with field data of demographic surveys. Moreover, a high degree of genetic differentiation (F(ST) = 0.535; G(ST) = 0.608; theta(B) = 0.607) was detected among populations and no correlation was found between geographical and genetic distance, suggesting that populations were in disequilibrium of migration-drift. Genetic drift played a more important role than gene flow in the current population genetic structure of I. sinensis because migration of I. sinensis is predominantly water-mediated and habitat range was highly influenced by environment changes. CONCLUSIONS: Genetic information obtained in the present study provides useful baseline data for formulating conservation strategies. Conservation management, including both reinforcement for in situ populations and ex situ conservation programmes should be carefully designed to avoid the potential risk of outbreeding depression by admixture of individuals from different regions. However, translocation within the same regional population should be considered as a measure of genetic enhancement to rehabilitate local populations. An ex situ conservation strategy for conserving all extant populations to maximize genomic representation of the species is also recommended.     

Genetic structure of wild and cultivated olives in the central Mediterranean basin

BACKGROUND AND AIMS: Olive cultivars and their wild relatives (oleasters) represent two botanical varieties of Olea europaea subsp. europaea (respectively europaea and sylvestris). Olive cultivars have undergone human selection and their area of diffusion overlaps that of oleasters. Populations of genuine wild olives seem restricted to isolated areas of Mediterranean forests, while most other wild-looking forms of olive may include feral forms that escaped cultivation. METHODS: The genetic structure of wild and cultivated olive tree populations was evaluated by amplified fragment length polymorphism (AFLP) markers at a microscale level in one continental and two insular Italian regions. KEY RESULTS: The observed patterns of genetic variation were able to distinguish wild from cultivated populations and continental from insular regions. Island oleasters were highly similar to each other and were clearly distinguishable from those of continental regions. Ancient cultivated material from one island clustered with the wild plants, while the old plants from the continental region clustered with the cultivated group. CONCLUSIONS: On the basis of these results, we can assume that olive trees have undergone a different selection/domestication process in the insular and mainland regions. The degree of differentiation between oleasters and cultivated trees on the islands suggests that all cultivars have been introduced into these regions from the outside, while the Umbrian cultivars have originated either by selection from local oleasters or by direct introduction from other regions.     

省沽油群体遗传多样性的AFLP分析

利用4对AFLP引物对来自安徽石台、湖北大悟和河南桐柏的3个省沽油群体进行遗传多样性分析,共扩增出489条带,其中多态性条带460条,多态性百分比为93.99%。不同群体Nei’s基因多样性指数(H)和Shannon’s信息指数(I)变化范围分别为0.1920～0.2046和0.2937～0.3151,其中湖北大悟群体遗传多样性最高。物种水平和种群水平的H分别为0.2190和0.1964,群体内变异占总变异的89.68%,表明省沽油遗传变异主要存在于各群体内部。3个群体的平均遗传距离为0.0292,UPGMA聚类分析结果说明省沽油各群体间亲缘关系较近并和地域具有相关性。建议省沽油的遗传资源保护应以种内遗传多样性的保护为主。     

Genetic population structure, fitness variation and the importance of population history in remnant populations of the endangered plant Silene chlorantha (Willd.) Ehrh. (Caryophyllaceae)

Habitat fragmentation can lead to a decline of genetic diversity, a potential risk for the survival of natural populations. Fragmented populations can become highly differentiated due to reduced gene flow and genetic drift. A decline in number of individuals can result in lower reproductive fitness due to inbreeding effects. We investigated genetic variation within and between 11 populations of the rare and endangered plant Silene chlorantha in northeastern Germany to support conservation strategies. Genetic diversity was evaluated using AFLP techniques and the results were correlated to fitness traits. Fitness evaluation in nature and in a common garden approach was conducted. Our analysis revealed population differentiation was high and within population genetic diversity was intermediate. A clear population structure was supported by a Bayesian approach, AMOVA and neighbour-joining analysis. No correlation between genetic and geographic distance was found. Our results indicate that patterns of population differentiation were mainly caused by temporal and/or spatial isolation and genetic drift. The fitness evaluation revealed that pollinator limitation and habitat quality seem, at present, to be more important to reproductive fitness than genetic diversity by itself. Populations of S. chlorantha with low genetic diversity have the potential to increase in individual number if habitat conditions improve. This was detected in a single large population in the investigation area, which was formerly affected by bottleneck effects.     

用扩增片段的长度多态性分子标记探讨盾叶薯蓣的遗传多样性

用扩增片段的长度多态性(amplified fragment length polymorphism,AFLP)标记分析研究了中国5个盾叶薯蓣居群30个个体的遗传多样性。筛选出9对AFLP引物,从中检测到14698条清晰可见的条带,其中多态性带12628条,多态性比率85.92%。Shannon信息指数(I)为0.3656±0.1721,物种水平的Nei基因多样性(H)为0.2322±0.2200。遗传变异分析表明,物种水平的遗传分化系数Gst为0.4827,说明其群体间存在一定的遗传分化,居群间的基因流Nm为0.5358,居群间遗传交换较小。聚类分析结果显示5个居群盾叶薯蓣有较为丰富的遗传变异,且与地理分布有相关性。     

中国二化螟不同地理种群的AFLP遗传分析

利用AFLP标记对中国11省13个二化螟Chilo suppressalis(Walker)地理种群进行遗传多态性分析,以揭示不同区域种群间遗传分化,为建立较准确的二化螟发生区划及区域治理对策提供新的依据。选取3对引物,共扩增出445个位点,其中多态性位点数为386,多态性比率为86.8%。种群间分化系数(Gst)为0.74,基因流仅为0.176;13个地理种群间遗传一致度较高,均大于0.67。遗传距离聚类分析表明,二化螟13个地理种群可区分为4类,其中淮北平原类(赣榆、阜宁、阜南)、东南山区类(鄞县、闽侯)、荆湘川类(荆州、邵阳、德阳)三类种群分别具有较一致的地理气候特征或相对较近的距离。研究还表明,与其他测试种群的遗传距离普遍较大、相对孤立的地理种群,其聚类结果有一定的随机性,因此,取样点较多、且样点分布较均匀的聚类分析结果才有较高可信度。     

Population Genetic Structure of Neotropical Mangrove Species on the Colombian Pacific Coast: Pelliciera rhizophorae (Pellicieraceae)1

Pelliciera rhizophorae is a Neotropical mangrove species whose distribution is mostly restricted to the Pacific Coast, between the Gulf of Nicoya (Costa Rica) and the Esmeraldas River (Ecuador). In the Caribbean, patches of Pelliciera have been found in Nicaragua, Panama, and Colombia. The genetic variation and the population structure of P. rhizophorae were evaluated in six zones of the Colombian Pacific, using AFLP molecular markers. Of the 225 amplified fragments produced, 155 (69%) were polymorphic in 57 individuals of P. rhizophorae collected in the localities of Virudó, Charambirá, La Plata Island, Tumaco, Milagros, and Chontal. Genetic diversity within populations varied significantly, with the lowest levels of within‐population variation (H_ep= 0.081 and 0.090, respectively) in La Plata Island and Tumaco; and the highest level of variation (H_ep= 0.187) in Chontal. In the Colombian Pacific, P. rhizophorae was significantly structured, with 26.5 percent of the variation found among populations, which was an evidence of substructure within populations. Genetic differentiation was not related to the geographic distance between zones. This suggests that the population dynamics of P. rhizophorae could be associated with historic processes influenced by ecological and environmental factors such as the movement of pollen by birds, the displacement of propagules by marine currents, and the spatial distribution of favorable habitats.