桂东南地区普通野生稻遗传多样性研究

利用25个微卫星位点对广西壮族自治区贺州、崇左、防城港3市8个居群301份普通野生稻材料的遗传多样性和遗传结构进行研究,结果表明桂东南地区普通野生稻遗传多样性丰富,平均等位基因数A=10.2400,有效等位基因数Ae=5.0221,平均期望杂合度He=0.7641,实际观察杂合度Ho=0.4840.根据固定指数(F=0.5653)计算出的异交率(t=0.2777)表明,普通野生稻的繁育系统是典型的混合繁育系统.对其遗传结构分析表明,总的遗传变异中有34.59%存在于居群间(Fst=0.3459).进一步研究发现大多数居群偏离了Hardy-Weinberg平衡且杂合体不足(Fis=0.2680,Fit=0.4817).最后根据各居群的遗传变异特点和遗传多样性比较,建议居群QT、YJ和TJ需要优先保护.     

利用SSR标记分析海南普通野生稻的遗传多样性

选用平均分布于水稻基因组的28对SSR引物,对海南不同纬度5个普通野生稻居群的163份材料进行遗传多样性和遗传结构研究。结果表明:(1)海南普通野生稻具有较高的遗传多样性,28个位点共检测到227个等位变异,平均等位变异数A=8.1071,有效等位变异数Ae=4.4190,平均期望杂合度He=0.4004,实际观察杂合度Ho=0.7062,香农指数I=1.6048;(2)居群的遗传分化系数较大,总的遗传变异中有46.40%存在于居群间(Fst=0.4640);(3)居群内杂合体较高(F is=-0.7069),根据固定指数(F=0.0588)计算出的异交率t=0.8889,说明海南普通野生稻的繁育系统属于一种较高的异交混合交配类型。     

利用SRAP标记研究海南野生稻的遗传多样性与遗传分化

利用8对多态性较好的SRAP引物对海南120份普通野生稻、55份疣粒野生稻和26份药用野生稻进行扩增,在检测到的219个位点中,普通野生稻的多态性位点率为74.89％,疣粒野生稻为42.47％,药用野生稻25.11%。香农指数以普通野生稻最高0.3277,疣粒野生稻为0.2044,药用野生稻最低0.1113。UPGMA聚类分析结果显示供试材料与地理来源相一致,相关性强,各居群个体间没有出现任何交叉。根据居群间的遗传分化系数,普通野生稻群体的基因多样性为0.2135,群体内的平均基因多样性大于居群间的基因漂变,说明普通野生稻居群遗传分化不显著,遗传多样性主要来自于居群内,基于群体杂合度和居群遗传多样性指数特点,认为实施保护策略时,优先保护遗传多样性最丰富的WDL和WDA居群。疣粒野生稻居群存在中等程度的遗传分化,建议原生境保护;药用野生稻居群数量较少,建议原生境保护。     

用SSR标记分析福建漳浦野生稻的遗传多样性

应用平均分布于水稻基因组的21对SSR引物,对福建漳浦野生稻、海南野生稻共计62份材料的遗传多样性进行分析.结果表明:漳浦野生稻具有较高的遗传多样性,21个位点共检测到74个等位变异,平均等位变异数A=3.5238,有效等位变异数Ae=2.0629.平均期望杂合度He=0.4635,实际观察杂合度Ho=0.2465,香农指数I=0.8286;根据固定指数(F=0.3887)估算的异交率t=0.4308,说明漳浦野生稻的繁育系统属于一种自交率较高的混合交配类型;分化程度石潭湖群体高于古塘群体.     

广西普通野生稻(Oryza rufipogon Griff)表型性状和SSR多样性研究

以中国普通野生稻初级核心种质中广西普通野生稻部分中的 2 2 3份野生稻为材料 ,以平均分布于水稻 12条染色体上的 34对SSR引物和中国稻种资源目录中的表型性状分析广西普通野生稻SSR位点的等位变异、多样性的地理分布及不同生长习性间的多样性分布等。结果表明 ,每对引物检测到的多态性片段 7～ 4 8条 ,平均为 2 4 .91条 ,普通野生稻的等位变异数明显大于地方稻种 ,在所分析的SSR位点中杂合位点比例变化在 1.35 %～ 81.31%之间 ,平均为 32 .0 1% ,与自花授粉的栽培稻相比具有较高的杂合率 ;北纬 2 2°～ 2 3°和 2 3°～ 2 4°范围内的两个区域内(一个包括隆安、扶绥和邕宁三县 ,另一个包括象州、来宾、武宣、玉林和贵港五个县 )所包含的普通野生稻数量多 ,遗传多样性大 ,在DNA水平上是广西普通野生稻的遗传多样性中心 ,而表型性状多样性中心是在北纬 2 1°～ 2 2°和2 2°～ 2 3°,其多样性分布与DNA水平不完全一致。在 4种生长习性间 ,DNA水平上的遗传多样性大小依次为匍匐型 ,倾斜型 ,半直立型和直立型 ,表型水平的多样性与DNA水平的多样性基本一致。     

普通野生稻保护和未保护居群遗传多样性的比较

为了评价普通野生稻自然居群遗传多样性,用24对SSR引物对5个保护居群（江西东乡庵家山JXD、湖南茶陵HNC、湖南江永HNJ、广东高州大岭GDD、海南儋州HND）和3个未保护居群（广西武宣GXW、广西来宾GXL、广东高州朋山GDP）,共计356个单株进行了遗传多样性分析。24个位点均表现为多态,其中18个位点表现杂合子不足,RM339位点观察杂合度最高,RM336位点预期杂合度最高。SSR分析结果表明,8个居群的遗传多样性都较高,其中5个保护居群的Ae变幅为1．780（JXD）～2．504（HNJ）,肌变幅为0．397（JXD）～0．555（HNJ）;3个未保护居群Ae变幅为2、153（GDP）～3．226（GXL）．He变幅为0．492（GDP）～0．640（GXL）。5个保护居群与3个未保护居群之间的遗传距离较大（0．6585）。这说明虽然有些居群得到了保护,但未保护居群的保护、收集价值仍然很大。居群间遗传分化明显（Fst=0．399）,居群间遗传距离最小的HNJ居群与GXL居群的相似系数也只有0．43。F一统计显示所用居群都偏离了Hardy—Weinbery平衡（Fis=0．147）,其中GDD、GDP、HND居群Fis〈0,表现为杂合子过剩;居群JXD的Fis为0．109,表现轻微的杂合子缺乏;HNC、HNJ、GXW、GXL的F括〉0,Fis值变幅为0．315（GXW）～0．473（HNJ）,说明这4个居群中杂合子不足,可能与这些居群自交比例高有关。     

普通野生稻（Oryza rufipogon Griff．）的SSR遗传多样性研究

利用SSR标记对分布在我国7个省的17个居群普通野生稻(Oryza rufipogon Griff．)的种质资源进行研究,结果表明：17个居群普通野生稻的遗传多样性有着显著的差异,从UPGMA聚类结果可以看出普通野生稻的遗传多样性与其生态地理分布有显著的相关性,遗传多样性指数高的地区极有可能是栽培稻的起源中心;用筛选出的7对SSR引物对336份：DNA样品进行扩增,得到60条特异条带,在分子水平上进一步证明普通野生稻的起源为两广地区;本研究也表明SSR是进行遗传资源多样性研究的一种切实有效的研究方法。     

云南元江普通野生稻(Oryza urfipogon Griff)遗传多样性分析及保护策略研究

用SSR方法对云南元江普通野生稻3个自然居群进行30个位点的遗传多样性分析.结果表明,元江普通野生稻具有较高的遗传变异水平(Ap＝2.6,Hs=0.77),且群体遗传分化系数较大,GST为41.08%,即在遗传变异总量中41.08%存在于居群间.本文还通过对云南元江普通野生稻遗传多样性特点的分析,提出了保护策略.     

植物种群交配系统、亲本分析以及基因流动研究

 在过去的二十年中,有关植物种群交配与散布过程的研究与日俱增,重点集中在利用母本子代系列(Maternal progeny arrays)来估计种群间自交与异交的相对比例,种群的花粉散布与雄性育性变异的模式。早期的研究主要依靠排除法来确定亲本,但几乎同时也意识到基因流动事件几乎是检测不到的。在大多数估计中,难以做到为大多数非迁移子代确定唯一的亲本。因此,基因流动与雄性育性的最大似然性方法得以引入该领域的研究。本文介绍了用单位点和多位点模型来估计家系与种群自交与异交的相对频率,着重阐述了目前可用于亲本分析与基因流的估计方法。最后介绍了我们对木根麦冬交配系统与亲本分析的研究以及亲本分析将来的研究方向。     

迁地保护中普通野生稻和长喙毛莨泽泻种群动态及评价

通过对江西东乡含濒危植物普通野生稻和长喙毛莨泽泻的群落在余江县实施重建，研究并评价了迁地保护后的濒危植物种群动态。结果表明，普通野生稻种群呈迅速增长的趋势，分布面积迅速扩大，有性繁殖正常，实生苗补充在种群增长中起重要作用；     

Increased inbreeding but not homozygosity in small populations of Sabatia angularis (Gentianaceae)

Understanding how the mating system varies with population size in plant populations is critical for understanding their genetic and demographic fates. We examined how the mating system, characterized by outcrossing rate, biparental inbreeding rate, and inbreeding coefficient, and genetic diversity varied with population size in natural populations of the biennial Sabatia angularis. We found a significant, positive relationship between outcrossing and population size. Selfing was as high as 40% in one small population but was only 7% in the largest population. Despite this pattern, observed heterozygosity did not vary with population size, and we suggest that selection against inbred individuals maintains observed heterozygosity in small populations. Consistent with this hypothesis, we found a trend of lower inbreeding coefficients in the maternal than progeny generation in all of the populations, and half of the populations exhibited significant excesses of adult heterozygosity. Moreover, genetic diversity was not related to population size and was similar across all populations examined. Our results suggest that the consequences of increased selfing for population fitness in S. angularis, a species that experiences significant inbreeding depression, will depend on the relative magnitude and consistency of inbreeding depression and the demographic cost of selection for outcrossed progeny in small populations.     

Limiting inbreeding in disjunct and isolated populations of a woody shrub

Pollen movements and mating patterns are key features that influence population genetic structure. When gene flow is low, small populations are prone to increased genetic drift and inbreeding, but naturally disjunct species may have features that reduce inbreeding and contribute to their persistence despite genetic isolation. Using microsatellite loci, we investigated outcrossing levels, family mating parameters, pollen dispersal, and spatial genetic structure in three populations of Hakea oldfieldii, a fire‐sensitive shrub with naturally disjunct, isolated populations prone to reduction in size and extinction following fires. We mapped and genotyped a sample of 102 plants from a large population, and all plants from two smaller populations (28 and 20 individuals), and genotyped 158–210 progeny from each population. We found high outcrossing despite the possibility of geitonogamous pollination, small amounts of biparental inbreeding, a limited number of successful pollen parents within populations, and significant correlated paternity. The number of pollen parents for each seed parent was moderate. There was low but significant spatial genetic structure up to 10 m around plants, but the majority of successful pollen came from outside this area including substantial proportions from distant plants within populations. Seed production varied among seven populations investigated but was not correlated with census population size. We suggest there may be a mechanism to prevent self‐pollination in H. oldfieldii and that high outcrossing and pollen dispersal within populations would promote genetic diversity among the relatively small amount of seed stored in the canopy. These features of the mating system would contribute to the persistence of genetically isolated populations prone to fluctuations in size.     

Fine-scale genetic structure enhances biparental inbreeding by promoting mating events between more related individuals in wild soybean (Glycine soja; Fabaceae) populations

Outcrossing between genetically distant individuals in a plant population enhances allelic heterozygosity-an important source for genetic diversity and adaptive evolution. Fine-scale spatial genetic structure (FSGS) can interfere with outcrossing by promoting mating between more related individuals. To test the influence of FSGS on outcrossing, FSGS and outcrossing rates were analyzed with four wild soybean (Glycine soja) populations from different habitats, using simple sequence repeat (SSR) fingerprints. Spatial autocorrelation analysis indicated variable FSGS (15.44-25.87 m) in all four populations. Multilocus mixed-mating analysis of 1605 progeny indicated substantial variation in single-locus outcrossing (T(s) = 6.3-12.6%) although the total outcrossing rates as estimated by multilocus outcrossing (T(m) = 12.8-17%) did not vary significantly among populations. The comparison between FSGS and outcrossing rates demonstrated that strong FSGS with large genetic patch size can enhance biparental inbreeding by promoting mating between more related individuals in a population. The results suggest that patch size management can aid in situ conservation by avoiding formation of strong FSGS and encouraging true outcrossing among individuals.     

Conservation implications of the mating system of the Pampa Hermosa landrace of peach palm analyzed with microsatellite markers

Peach palm (Bactris gasipaes) is cultivated by many indigenous and traditional communities from Amazonia to Central America for its edible fruits, and is currently important for its heart-of-palm. The objective of this study was to investigate the mating system of peach palm, as this is important for conservation and breeding. Eight microsatellite loci were used to genotype 24 open-pollinated progenies from three populations of the Pampa Hermosa landrace maintained in a progeny trial for genetic improvement. Both the multi-locus outcrossing rates (0.95 to 0.99) and the progeny level multi-locus outcrossing rates (0.9 to 1.0) were high, indicating that peach palm is predominantly allogamous. The outcrossing rates among relatives were significantly different from zero (0.101 to 0.202), providing evidence for considerable biparental inbreeding within populations, probably due to farmers planting seeds of a small number of open-pollinated progenies in the same plot. The correlations of paternity estimates were low (0.051 to 0.112), suggesting a large number of pollen sources (9 to 20) participating in pollination of individual fruit bunches. Effective population size estimates suggest that current germplasm collections are insufficient for long-term ex situ conservation. As with most underutilized crops, on farm conservation is the most important component of an integrated conservation strategy.     

Microsatellite variation within and among populations of Oryza officinalis (Poaceae), an endangered wild rice from China

Oryza officinalis Wall. ex Watt. is an agriculturally important but seriously endangered species of wild rice. To obtain more accurate estimates of population structure for improved conservation planning of the species, genetic variability at 14 microsatellite DNA loci was examined in population samples covering most of the species' range in China. Considerable genetic variability (overall Na = 1.886, P = 62%, HO = 0.056, HE = 0.216, and HS = 0.277) was detected at the 14 loci in 442 individuals of the 18 natural populations. The evaluation of partitioning of genetic variability (FST = 0.442) suggested high genetic differentiation among the Chinese O. officinalis populations. An overall value of Nm = 0.316 suggested limited gene flow occurred among the sampled populations. Most of the populations showed heterozygote deficits in tests of Hardy-Weinberg equilibrium and significantly positive FIS values. This could be due to some inbreeding occurring in this predominantly outcrossing species. For effective in situ conservation and restoration genetics, maintenance of significant historical processes is particularly important, including high outbreeding, considerable gene flow, and large population effective sizes. The high FST values detected among populations in this study are instructive for adopting a conservation plan that includes representative populations with the greatest genetic variation for either in situ conservation management or germplasm collection expeditions.     

Population structure and conservation genetics of wild rice Oryza rufipogon (Poaceae): a region-wide perspective from microsatellite variation

Oryza rufipogon Griff. is the most agriculturally important but seriously endangered wild rice species. To better estimate how genetic structure can be used to obtained a conservation perspective of the species, genetic variability at six polymorphic microsatellite DNA loci was examined. High levels of genetic variability were detected at six loci in 1245 individuals of 47 natural populations covering most of the species' range in China (overall RS = 3.0740, HO = 0.2290, HS = 0.6700). Partitioning of genetic variability (FST = 0.246) showed that most microsatellite variation was distributed within populations. Significant departures from Hardy-Weinberg expectations and very strong linkage disequilibrium indicate a high degree of inbreeding in the species and severe subdivision within populations. A mean Nm value of 0.7662 suggested a limited gene flow among the assayed populations. Our study suggests that conservation and restoration genetics should focus in particular on the maintenance of historically significant processes such as high levels of outbreeding and gene flow and large effective population size in the species.     

Intra-Population Genetic Structure of Oryza rufipogon Griff. in Yunnan, China

Oryza rufipogon Griff., allozyme analysis was conducted using 22 loci on a typical population from Yunnan Province, China. Non-random distribution of genotypes and/or genetic variability was found among three subpopulations, and the result was further demonstrated by considerable genetic differentiation observed (F _ST =0.206) within the population. Microhabitat selection may not be an important factor in shaping intra-population genetic structure, and restricted gene flow (N _m =0.964<1) and genetic drift act together towards a genetic subdivision within the population. This genetic subdivision may enhance inbreeding and will ultimately lead to genetic depletion within the predominantly outcrossing (t=0.830) perennial population, and therefore, more attention should be paid to the conservation and genetic management of the population. Received 25 June 1999/ Accepted in revised form 31 August 2000     

Extensive long-distance pollen dispersal and highly outcrossed mating in historically small and disjunct populations of Acacia woodmaniorum (Fabaceae), a rare banded iron formation endemic

Background and Aims

Understanding patterns of pollen dispersal and variation in mating systems provides insights into the evolutionary potential of plant species and how historically rare species with small disjunct populations persist over long time frames. This study aims to quantify the role of pollen dispersal and the mating system in maintaining contemporary levels of connectivity and facilitating persistence of small populations of the historically rare Acacia woodmaniorum.

Methods

Progeny arrays of A. woodmaniorum were genotyped with nine polymorphic microsatellite markers. A low number of fathers contributed to seed within single pods; therefore, sampling to remove bias of correlated paternity was implemented for further analysis. Pollen immigration and mating system parameters were then assessed in eight populations of varying size and degree of isolation.

Key Results

Pollen immigration into small disjunct populations was extensive (mean minimum estimate 40 % and mean maximum estimate 57 % of progeny) and dispersal occurred over large distances (≤1870m). Pollen immigration resulted in large effective population sizes and was sufficient to ensure adaptive and inbreeding connectivity in small disjunct populations. High outcrossing (mean t_m = 0·975) and a lack of apparent inbreeding suggested that a self-incompatibility mechanism is operating. Population parameters, including size and degree of geographic disjunction, were not useful predictors of pollen dispersal or components of the mating system.

Conclusions

Extensive long-distance pollen dispersal and a highly outcrossed mating system are likely to play a key role in maintaining genetic diversity and limiting negative genetic effects of inbreeding and drift in small disjunct populations of A. woodmaniorum. It is proposed that maintenance of genetic connectivity through habitat and pollinator conservation will be a key factor in the persistence of this and other historically rare species with similar extensive long-distance pollen dispersal and highly outcrossed mating systems.     

The cost of inbreeding in Platanthera leucophaea (Orchidaceae)

Fragmentation and isolation are expected to have a considerable impact on viability and recruitment in populations of rare species. Platanthera leucophaea (Orchidaceae), a rare orchid, currently exists in a fragmented landscape of its natural habitat. Floral morphology suggests this species is predominantly outcrossing, but surveys of allozyme diversity suggest high, variable levels of inbreeding in populations (F(IS) = -0.078 to 1.0). This study examines the potential cost of inbreeding and the extent to which inbreeding depression can vary temporally and in populations of different size and genetic structure. Flowers were pollinated by hand in one large population and one small population over three seasons. Seed set, seed mass, and seed viability were compared among self-, outcross-, and open-pollinated fruits. Seed set was greater than 50% in both populations for all years of study. High levels of inbreeding depression were detected in seed viability but not in seed mass in both populations. However, the magnitude of inbreeding depression differed over years and between populations, a pattern that reflects differing environmental conditions and variable evolutionary and demographic histories. Consequently, conservation of this species will be most successful if outcrossing is promoted in populations by maximizing population size and genetic variability.     

The effect of mating system on growth of Arabidopsis lyrata in response to inoculation with the biotrophic parasite Albugo candida

The effects of variation in host reproductive systems on response to pathogens are not well understood. We inoculated individuals from outcrossing and inbreeding populations of North American Arabidopsis lyrata with Albugo candida (white blister rust) to test the effect of mating system and heterozygosity on disease response. We observed three host infection phenotypes, classified as fully resistant, partially resistant and fully susceptible. Overall, inbreeding populations had more susceptible and fewer partially resistant individuals than outcrossing populations, but the highest proportion of resistant individuals was found in two of the inbreeding populations. Mating system did not affect relative growth rate of inoculated plants, but there were strong effects of population and infection phenotype. We conclude that mating system per se does not determine the resistance of natural A. lyrata populations to infection by Albugo, but that the increased variability in responses among inbreeding populations may be due to reduced effective population size.