首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 62 毫秒
1.
Baobab (Adansonia digitata L) belonging to Bombacaceae family, is one of the most widely used indigenous priority tree species in sub-Saharan Africa, valued in the cosmetic industry for its seed oil, and powdery fruit pulp for juice making. Baobab has high potential for domestication in southern Africa, therefore understanding its genetic diversity and population structuring is warranted. The study investigated the level of genetic diversity and differentiation of five populations of A. digitata L. sampled from four diverse silvicultural zones in Malawi. Variation at nine microsatellite loci were examined in 150 individual trees. Low mean genetic diversity was expressed through genetic diversity indices: Nei’s genetic diversity (h, 0.18 ± 0.03), Shannon Information Index (I, 0.21 ± 0.07), observed number of alleles (na, 1.47 ± 0.10), effective number of alleles (ne, 1.23 ± 0.04) and percentage polymorphic loci (pp, 48 %). The low genetic variation found is attributed to the population growing in marginal areas of genetic centre of diversity of the species, anthropogenic factors and founder effects. Moderate genetic differentiation was observed among populations (Gst = 0.13) indicating the presence of a large number of common alleles resulting in a homogenisation effect. Clustering of individual trees by genetic similarity coefficients indicated that mainland trees were genetically closer than the trees on Likoma Island. Mantel’s test showed a weak positive insignificant correlation (Z = 0.12; P = 0.64) between genetic distance among populations and actual distance on the ground implying that geneflow was not directly influenced by isolation by distance. The results suggest that seed distribution and tree improvement should recognise the presence of ecotypes and conservation measures should protect all the populations due to existence of private alleles which are of adaptive importance.  相似文献   

2.
World hazelnut production is based on European hazelnut (Corylus avellana) and is limited by the narrow climatic requirements of this species. The cold hardiness and disease resistance of the American hazelnut (Corylus americana) offer opportunities to expand production to new areas including the Upper Midwest (USA). The American hazelnut is a phenotypically diverse species. This study used ten microsatellite marker loci to investigate genetic diversity in 1140 individuals sampled from 25 populations across Wisconsin, Iowa, Minnesota and North Dakota. Overall, the marker loci were highly polymorphic (Ho = 0.69, He = 0.78, PIC = 0.84) with 7–13 alleles per locus. There was very high genetic diversity within populations (90% of the total) and some tendency toward population differentiation. Mantel’s test showed that genetic distance among the populations was not correlated with geographic distance. We conclude that selection of individuals for use in breeding should be based primarily on phenotype (productivity, nut size, percent kernel, ease of harvest), with care to include representatives of genetically differentiated populations.  相似文献   

3.
Taxus chinensis and T. wallichiana in have been threatened in their distribution areas in recent decades because of their over-exploitation and reduction and destruction of native habitats. Determining the genetic diversity in populations of the two species will provide guidelines for their protection and preservation. Two hundred and fifteen trees from six populations of T. chinensis and 150 sampled trees of T. wallichiana were sampled. Six microsatellite primer pairs selected from 16 primer pairs were used to investigate genetic variation at the population and species levels. Five yielded polymorphic alleles, and among the 13 putative alleles amplified, 11 were polymorphic (accounting for 76.33 %).Shannon’s information index (I) and percentage of polymorphic bands (PPB) (I = 0.202 and PPB = 67.22 % for T. chinensis; I = 0.217 and PPB = 65.03 % for T. wallichiana). Both species had low levels of genetic diversity (mean H o = 0.107, H e = 0.121 for T. chinensis; H o = 0.095, H e = 0.109 for T. wallichiana). Genetic differentiation among populations was higher (F ST = 0.189) for T. chinensis and lower (0.156) for T. wallichiana, indicating limited gene flow (Nm) among populations for T. chinensis (0.68) and T. wallichiana (0.65). Variation among individuals of T. chinensis was 63.59 and 73.12 % for T. wallichiana. Thus, the threatened status of the two conifers is related to a lack of genetic diversity. All populations are isolated in small forest remnants. An ex situ conservation site should be established with a new population for these species that comprises all the genetic groups for the best chance to improve their fitness under environmental stresses.  相似文献   

4.
The agricultural landscape of the United States could soon be changed by planting of switchgrass (Panicum virgatum L.) cultivars to meet government-mandated targets for lignocellulosic bioenergy production and consumption. This alteration could affect the genetic structure of wild switchgrass populations, which are native to the eastern half of North America through cultivar introgression. In this study, PCR amplification of microsatellite fragments as well as chloroplast gene-specific markers were utilized to quantify the genetic diversity and structure of five native populations and three agronomic fields (hereafter ‘populations’) planted with switchgrass cultivars. Microsatellite polymorphism across all the switchgrass populations ranged from 91.4 to 100 %. Overall, natural switchgrass populations had significantly higher mean genetic diversity than agronomic switchgrass cultivars (0.262 ± 0.102 and 0.201 ± 0.082 respectively, t test p < 0.008). Natural switchgrass populations had significantly higher total genetic diversity within (HS) and among (HT) as compared to agronomic switchgrass cultivars. A clear separation of natural and agronomic switchgrass populations was noted using principal component analysis and STRUCTURE analysis. A grouping pattern similar to that obtained in the microsatellite study was observed when chloroplast nucleotide sequence variation was assessed. In the realm of bioenergy sustainability, our results highlight the need to consider the genetic structure of cultivars for bioenergy when they are grown in proximity to native switchgrass populations.  相似文献   

5.
The early post-fire development of mycobiota following a crown fire in mountain pine plantations and a surface fire in Scots pine plantations, and in the corresponding unburnt stands in the coastal sand dunes of the Curonian Spit in western Lithuania was investigated. Species numbers in unburnt Pinus mugo and Pinus sylvestris stands showed annual fluctuation, but in the burnt sites, the numbers of fungi increased yearly, especially in the crown fire plots. Both burnt stand types—P. mugo and P. sylvestris—showed strongly significant (two-way ANOSIM; R = 1, p < 0.05) differences in species composition; the differences between unburnt sites were clearly expressed but less significant (R = 0.86, p < 0.05). Fungal species composition of burnt P. mugo and P. sylvestris sites was qualitatively different from that of corresponding unburnt sites (two-way ANOSIM; R ≥ 0.75, p < 0.05). The chronosequence of mycobiota in surface fire burns was less clearly defined than in crown fire sites, reflecting the greater patchiness of impacts of the surface fire. Although both fire types were detrimental or at least damaging to all functional groups of fungi (saprobic on soil and forest litter, wood-inhabiting, biotrophic, and mycorrhizal and lichenized fungi), their recovery and appearance (fructification) patterns varied between the groups and among the burn types. The end of the early post-fire fungal succession (cessation of sporocarp production of pyrophilous fungi) was recorded 3 years after the fire for both crown and surface fire types, which is earlier than reported by other authors. Rare or threatened fungal species that are dependent on fire regime were not recorded during the study.  相似文献   

6.
以20个云南松天然群体为对象,SSR分析表明云南松遗传变异主要存在于群体内,各群体间的遗传多样性水平差异不显著。基于SSR分子标记遗传多样性分析,根据Nei's遗传相似度,采用逐步聚类优先取样法,分别对初始群体、遗传多样性保护单元和剩余群体进行比较、t检验,以此评价遗传多样性保护单元的代表性。结果表明,利用该方法抽样的群体能很好地代表初始群体的遗传多样性,按30%的群体抽样,等位基因数、有效等位基因数、Shannon's信息指数和期望杂合度的保留率分别达到初始群体的98.03%、105.36%、103.99%和105.56%。保护单元的遗传多样性均高于剩余群体,抽样群体组成的遗传多样性保护单元的效果较好。  相似文献   

7.
Dothistroma needle blight (DNB) has been observed in Slovakia during the last two decades. Up until 2017, Dothistroma septosporum has only been detected and molecularly confirmed to cause DNB in Slovakia. Here, we report the detection of Dothistroma pini at six localities around Slovakia, representing different plantation types. Four pine species (Pinus sylvestris, P. nigra, P. mugo and P. jeffreyi) were confirmed as hosts of D. pini in Slovakia, of which only P. mugo has been previously reported as host in Slovakia. Three gene regions (ITS, EF1 –α, and ß-tubulin) of each of the 13 isolates were sequenced and assigned as D. pini. Based on ITS sequences, the studied isolates represent the haplotypes Dp_HAP.1, Dp_HAP.2. Both mating types were detected but at different localities. Our results suggest that in addition to D. septosporum, D. pini may contribute to DNB also in Slovakia.  相似文献   

8.
Pieris japonica is a poisonous tree species that is rarely eaten by herbivorous animals, a fact that could enable the expansion of its distribution range and influence ecosystems into which it encroaches. In a regional-scale study, 300 P. japonica trees from 13 populations were sampled at the University of Tokyo Chichibu Forest, Japan, and were analyzed using 11 microsatellite markers. Genetic differentiation among the populations was low (F ST = 0.022 and G′ ST = 0.024). A plot (30 × 30 m) was established for a fine-scale study, in which all P. japonica trees and saplings were measured and genetically analyzed using the microsatellite markers. Using this approach, we detected 84 genotypes among the 121 P. japonica trees in the plot. A few genotypes had expanded by more than 5 m, indicating that the ability to reproduce asexually could facilitate P. japonica trees to remain in a given location. Autocorrelation analysis showed that the extent of nonrandom spatial genetic structure was approximately 7.0 m, suggesting that seed dispersal was limited. KINGROUP analyses showed that 44 genotype pairs were full siblings, 23 were half-siblings, and 40 were parent-offspring. Only 32 seedlings were observed, of which 15 had reproduced asexually. The number of P. japonica trees has been increasing gradually for more than half a century in our study areas.  相似文献   

9.
Large-scale reforestation programmes are a major source of unwarranted gene flow and can have profound consequences on local genetic diversity. Recently, ash has been introduced to Ireland from continental Europe to stock plantations but has often exhibited poor stem form. It was not known whether these trees were Fraxinus excelsior, Fraxinus angustifolia or interspecific hybrids that are known to occur in continental Europe. F. excelsior is the only native ash in Ireland, so the introduced populations represent a potential threat for the genetic diversity of native populations. We characterized the introduced trees within two plantations (Clonee and Kildalkey) using morphological characters and six microsatellite markers. Samples from continental Europe were included for comparison. Plantations exhibited higher genetic diversity than control populations because our data suggest they contain a mixture of several provenances. There was a small but significant differentiation between plantations and control populations (ФCT = 0.0211). Bayesian analysis to infer population structure and to assign introduced individuals to reference populations clearly demonstrated the presence of hybrid individuals within the plantations. The percentage of trees detected with potential hybrid origin ranged from 28 to 58 % depending on the plantation and the threshold data analysis level chosen. Most hybrids could be considered cryptic because there was a lack of intermediate morphology for hybrid individuals that mainly clustered with F. excelsior. The results indicated that the source of material at the two plantation sites differed. Management options to minimize the impact of these introduced populations are discussed.  相似文献   

10.
The weevil, Curculio elephas (Coleoptera, Curculionidae), is one of the most abundant and widespread chestnut feeding pests in Greece. Together with the tortricid moths Cydia splendana and C. fagiglandana (Lepidoptera, Tortricidae), C. elephas greatly affect chestnut production. This weevil occurs in a continuous range throughout Greece; however, its population structure is unknown. Information concerning its population structure could help in the future control of this pest. A 790 bp portion of the mitochondrial Cytochrome Oxidase I gene was sequenced for 160 C. elephas larvae from ten populations. Compared to other Curculio species haplotype diversity with 31 haplotypes and nucleotide diversity with six nucleotide substitutions was low. The Bayesian inference of phylogeography in concert with nested clade analysis revealed a loose geographic distribution of genetic diversity that was likely the joint effect of isolation by distance and gene flow. In addition, population indices and Bayesian-based calculations showed that the populations of C. elephas in Greece are at the phase of expansion. Dating the phylogeny suggests about 300,000 years before present as the start of divergence among the populations of C. elephas in Greece.  相似文献   

11.
  • ? The genetic diversity of nine wild Tunisian Crataegus azarolus var. aronia L. populations from different bioclimates was assessed using RAPD markers.
  • ? Eight selected primers generated a total of 105 bands, 81 of which were polymorphic. Shannon’s index (H′) ranged from 0.222 to 0.278 according to a population with an average of 0.245. The genetic variation within the species (H SP = 0.423) was relatively low. A high differentiation (G ST = 0.421) among populations coupled with a low level of gene flow (N m = 0.472) were observed. The analysis of molecular variance (AMOVA) revealed also significant differentiation among populations (ΦST = 0.371), even at a low scale space. The majority of variation occurred within populations (63.31%). The Mantel test performed on genetic (ΦST) and geographic distance matrices among population pairs did not reveal an isolation by distance.
  • ? Interpretation of Neighbour-joining tree based on Nei’s and Li’s genetic distance among individuals showed distinct population groupings. The UPGMA dendrogram based on ΦST values revealed two population sub-clusters, each including populations from different bioclimates and/or geographic regions.
  • ? The low level of genetic diversity and the high genetic structure of populations resulted from genetic drift caused both by habitat fragmentation and the low size of populations.
  • ? The high differentiation among populations and the similar low level of diversity within populations suggest that in situ conservation should interest all populations. The ex situ conservation should be based on the collection of seeds rather within than among populations because of the maximum of variation was revealed within populations.
    •   相似文献   

    12.
    无患子天然居群遗传多样性研究   总被引：3，自引：0，他引：3       下载免费PDF全文
    [目的]通过我国无患子主要分布区的居群样本,研究无患子天然居群的遗传多样性和遗传结构.[方法]采用ISSR分子标记技术,利用12条ISSR引物分析18个天然居群的265株个体样本.[结果]表明无患子遗传多样性水平较高,物种和居群水平上的多态位点百分率 (PPB)分别为95.37%和57.82%,Shannon's信息指数(I)分别为0.256 9和0.199 8,Nei's遗传多样性指数(H)分别为0.390 9和0.298 0.AMOVA分析表明,18个居群间出现一定程度的遗传分化,且遗传变异主要发生在居群内.UPGMA聚类和Mantel检验结果表明,18个天然居群可分为2大组群,且居群间的地理距离与遗传距离之间不存在显著相关性(r=0.066 7,P=0.541 7>0.05).[结论]无患子以自交为主,其天然居群遗传多样性丰富,居群内的遗传多样性高于居群间.研究结果可为无患子育种策略的科学制定和种质资源的有效保护及利用提供理论依据.  相似文献   

    13.
    Nineteen Chinese populations of Castanopsis hystrix were examined to quantify genetic diversity and genetic structure at chloroplast DNA. Microsatellites (SSR) were analyzed by PCR using conserved primers. The average within population gene diversity (HS), the total gene diversity (HT), and the differentiation for unordered alleles (GST) and for ordered alleles (NST) were measured. Fourteen different haplotypes were detected, two of them very common. The level of differentiation among populations (GST = 23.6%) indicates a highly efficient seed dispersal mechanism. In addition, the difference between GST and NST for the species is not significant, suggesting that the phylogeographic structure is weak or absent. The geographical pattern of C. hystrix haplotypes could be attributed to its migration from the numerous and scattered refugia, where the species confined during the last glacial period. These results provide an important insight into patterns of postglacial recolonization of this tree species.  相似文献   

    14.
    The Azores provide an excellent field test for research activities aimed at developing conservation strategies for endangered tree species. In this work, the urgency to promote Picconia azorica conservation programs addressed (a) insights into the biotaxonomy of the species (including an evaluation of its origin and relationships with the only congeneric species of P. azorica: P. excelsa from the Canary and Madeira islands) and (b) the evaluation of P. azorica genetic diversity. Plastid DNA sequence analysis and molecular markers (RFLP and SSR) were used for this purpose. Phylogenetic data suggest the monophyly of Picconia and support a late Miocene divergence of the two species. Three polymorphic cpSSR loci allowed the identification of five different haplotypes in P. azorica. Uniqueness and relictuality of lineages are presented and discussed. Picconia azorica intra-specific diversity patterns revealed low genetic diversity and a weak genetic structure, which could result from long-lasting ecological stability and efficient inter-island seed movement that have been severely affected in recent times. The species survival is at risk, and we suggest management practices focusing on ex situ and in situ conservation units based on eco-genetic data. Additional measures contributing to mild erosion of the genepool and to remove barriers to seed dispersal are indicated.  相似文献   

    15.
    The Carpathians are a range of mountains forming an arc roughly 1,500 km long across Central and Eastern Europe. They are an important area for biodiversity and belong to one of the major refuges of the last ice ages for many organisms. The forests of the Carpathians are dominated by spruce, which have suffered continuous outbreaks of the eight spined spruce bark beetle, Ips typographus, in recent decades. The phylogeography of this spruce pest is well documented, however, little is known on small scale, i.e., the Carpathians. Here we applied a mitochondrial marker and studied the genetic variation and structure of Carpathian populations and compared data with published one from other European populations. Twelve haplotypes were characterized and 42 % of those were not detected in other European populations. Despite a slight genetic structure, differences were observed in the haplotype distribution and diversity between the Western/Southern Carpathians and the Eastern Carpathians reflecting at least two potential refugial areas for I. typographus within the Carpathian mountain system. Further data show that the Eastern Beskidian Mountains of the Carpathians could act as barrier for several European haplotypes. This small-scale analysis reveals that the Carpathians have been an important glacial and post-glacial refuge for I. typographus. This information is important for a preventive and reactive forest management.  相似文献   

    16.
    应用SSR标记技术,对新疆额尔齐斯河流域河谷分布的苦杨(Populus laurifoli)和欧洲黑杨(Populus nigra)天然居群的遗传多样性和遗传分化进行了研究。结果显示:苦杨和欧洲黑杨的天然居群具有较高的遗传多样性,且苦杨明显高于欧洲黑杨。与苦杨居群相比,欧洲黑杨居群间基因流较高,居群间的遗传分化程度较小,变异主要源于居群内。苦杨和欧洲黑杨居群内的杂合度较高,各个居群的各项遗传参数都要小于物种水平。苦杨和欧洲黑杨均偏离Hardy-Weinberg平衡,表现为杂合子过量的现象。  相似文献   

    17.
  • ? Genetic structures of five population pairs each consisting of one natural population and one neighbouring plantation of Pinus roxburghii Sarg. in Nepal were assessed using nuclear (nSSRs) and chloroplast microsatellite loci (cpSSRs).
  • ? The mean number of alleles at nSSRs loci in natural populations was 5.0 compared to 4.93 in plantations while the average observed heterozygosities were the same in both groups (H 0 = 0.50). Most of the alleles were common to all the populations, indicating that the populations correspond to a single genetic entity. Similarly forty-seven haplotypes were observed in natural populations compared to fifty haplotypes in plantations. Mean haplotype diversities of natural populations (0.953) and plantations (0.955) were very similar. Genetic diversity of Pinus roxburghii was relatively high with low or no evidence of inbreeding while genetic differentiation among all populations was very low (about 1%).
  • ? The very low differentiation among natural populations indicates efficient long-distance gene flow among populations resulting in homogeneous genetic structures at least at selectively neutral loci. Even though the harvest and production of seeds and seedlings was largely uncontrolled, genetic structures of most plantations show no signs of reduced variation, inbreeding or other negative effects compromising the adaptedness or adaptability of planted forests.
    •   相似文献   

    18.
    Assessment of genetic variation within and among populations is an essential parameter for the effective conservation of forest genetic resources. In this work, the genetic diversity within and among natural populations of the forest tree species Fraxinus angustifolia Vahl in Greece was studied using selected nuclear and chloroplast microsatellite DNA loci. Eight natural populations of F. angustifolia were identified in different locations of the mainland of Greece, and a total of 230 individuals were studied. High polymorphism was observed within populations, while the genetic differentiation among populations was moderate. Intra-population diversity was correlated with geographical coordinates, but no isolation by distance was observed. Of the three haplotypes identified, only one was dominant. Putative ancestral haplotypes were found at small spatial scales suggesting that population expansions could have originated in the region. This study located in sympatry haplotypes that in other parts of Europe are in allopatry, reinforcing the notion of population expansions from the south of Balkans including Greece. Suggestions for conservation and management of F. angustifolia are also reported.  相似文献   

    19.
    The “algarrobo” [Prosopis chilensis (Molina) Stuntz] is a tree species that represents an important natural resource in arid and semi-arid regions of Argentina. In this paper, we analysed and compared the variability of 46 RAPD (Random Amplified Polymorphic DNA) loci with previous estimates obtained from 12 isozyme markers in nine Argentinean populations of P. chilensis representative of the whole range of this species in Argentina. We evaluated the population structure and the existence of genetic variants associated with environmental variables. Expected heterozygosity (H e) estimated from RAPD varied significantly among populations and regions. Hierarchical analysis of genetic variability (AMOVA) showed that most (88.1%) of the total diversity occurs within populations, the component among populations within regions (9.3%) was intermediate, while the between-region component was the lowest (2.6%). All three variance components were highly significant. The MDS plot from pair-wise Φ ST matrix was consistent with the highly significant among-region differentiation indicated by the AMOVA. All 12 variable isozyme loci and 26 out of 46 RAPD loci showed significant or highly significant association with at least one geographic/climatic variable according to the stepwise multiple regression analysis. These results imply that the genetic differentiation among populations is better explained by environmental or biogeographical grounds than by geographical distances, suggesting gametic disequilibrium with loci responsible for the adaptation to particular environmental conditions. The information from RAPD markers would provide a relevant criterion to preserve genetic diversity in programmes for conservation and rationale use of this species.  相似文献   

    20.
    Pollen flow from external sources is important for the conservation of tree species in fragmented forests or small populations, because it can be sufficient to prevent differentiation among them, and appears to be able to prevent the loss of their genetic diversity through genetic drift. In this study, we examined the genetic heterogeneity of pollen pools accepted by each Quercus semiserrata seed parent at the Khun Wang Royal Agriculture Research Center, Thailand, both within and among two mast fruiting years (2005 and 2007), using paternity analysis and analysis of molecular variance (AMOVA). The mating systems of the trees were also examined using the multilocus mating system model (MLTR), after determining the genotypes at eight microsatellite loci of 26 seed-trees and 435 seeds from 8 seed-trees in the 2 mast fruiting years. The average distance of effective pollen flow within the plot was estimated to be 52.4 m, and 95% of effective pollen was dispersed within 200 m, indicating that effective pollen flow is highly localized and that most effective pollen is contributed by near-neighbor trees. The proportion of effective pollen that immigrated from external sources was estimated to be 26.2%. The AMOVA analysis based on the pollen haplotypes showed that the pollen pools, both total and for each reproductive year, significantly genetically differed among the seed parents. Using a mixed mating model, the estimate of biparental inbreeding for the total population (tm − ts) was 0.013, indicating that a low proportion of mating occurred among close relatives. The effective number of pollen donors (Nep) was estimated to be 9.987 using the TwoGener model, or 10.989 using the mixed mating model. The effective number of pollen donors of seeds was higher in the mast fruiting year 2005 than in the other examined year, 2007. Consequently the allelic richness and genetic diversity of seeds produced in 2005 were higher than those produced in 2007. Overall, the results show that high outcrossing rates, high levels of gene flow from other populations and heterogeneity in the pollen received by an individual may enhance the ability of populations to maintain effective population sizes. Therefore, these processes may be sufficient to prevent loss of genetic diversity through genetic drift of Q. semiserrata at this study site.  相似文献   

    设为首页 | 免责声明 | 关于勤云 | 加入收藏

    Copyright©北京勤云科技发展有限公司  京ICP备09084417号