Genetic structure and phylogeography in Juniperus oxycedrus subsp. macrocarpa around the Mediterranean and Atlantic coasts of the Iberian Peninsula, based on AFLP and plastid markers

The Spanish populations of Juniperus oxycedrus subsp. macrocarpa are restricted to coastal dune habitats of the Mediterranean and Atlantic coasts. Here, we investigate the genetic structure in this taxon and the possible existence of detailed phylogeographic structure associated with the Strait of Gibraltar using data from amplified fragment length polymorphism (AFLP) and plastid markers for 14 populations in three regions: Andalusia, the Valencian Community and the Balearic Islands. Principal coordinate analysis (PCOA) data revealed a lack of clear genetic structure in J. oxycedrus subsp. macrocarpa based on AFLP. The highest AFLP genetic diversity was found in Andalusia. Plastid markers revealed 14 haplotypes, only two of them were shared among the regions. Andalusian populations had the highest number of exclusive haplotypes. Our results support Andalusia as a reservoir of genetic diversity for J. oxycedrus subsp. macrocarpa, and, as for other gymnosperms, this area could be considered as a genetic refugium. The frequent presence of common and exclusive haplotypes in Andalusia might indicate the colonisation of the Spanish Mediterranean coast from the Atlantic populations. Colonisation of these new areas could be promoted by biological factors, such as the existence of long-lived individuals or potential for seed dispersal. Finally, the Strait of Gibraltar did not constitute a natural barrier to the expansion of this species along the coast, as identical haplotypes are found on the Atlantic and Mediterranean coasts.     

Phenotypic plasticity blurs ecotypic divergence in the response of <Emphasis Type="Italic">Quercus coccifera</Emphasis> and <Emphasis Type="Italic">Pinus halepensis</Emphasis> to water stress

The Mediterranean evergreen woody plants Quercus coccifera and Pinus halepensis grow in a range of environments where selection by drought, heat and high irradiance can drive genetic and phenotypic differentiation of populations. However, the role of these stresses in filtering out maladaptive genotypes remains unknown. We hypothesize that this filtering is an important process for woody Mediterranean species due to their low phenotypic plasticity reported in previous studies. We have studied the response of saplings of Q. coccifera and P. halepensis, originating from two contrasting populations (a rock outcrop and a garrigue formation), to water stress. Isozyme characterization of genetic diversity was done to determine whether populations were genetically distinct. Water response analysis was based on water relations, gas exchange, chlorophyll a fluorescence, pigment content, antioxidant status and morphological and structural parameters. Ecotypic differentiation was found for both Q. coccifera and P. halepensis populations, with a higher population isozyme similarity and a higher frequency of dominance of a few genotypes at the rock outcrop in both the species. P. halepensis exhibited small but significant differences between populations for plastic responses to water, with lower phenotypic plasticity in saplings from the rock outcrop. Although it was not found in Q. coccifera, this pattern suggests that ecotypic differentiation rendering stress-tolerant ecotypes involves a decreased plasticity. Phenotypic plasticity was not high but it explained over 75% of the total variability among individual plants. Thus, and although evidence for ecotypic divergence was found in both the species, saplings were plastic enough to blur ecotypic differentiation. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Genetic structure of plantations and the conservation of genetic resources of Brazilian pine (Araucaria angustifolia)

With growing concern about maintenance of genetic variation and conservation of gene resources, the question arises on the extent to which a planted population should be considered a resource able to preserve the gene pool of a species. In this study, levels of genetic diversity were assessed in natural and planted populations of Araucaria angustifolia using AFLPs and nuclear microsatellites, in order to assess the usefulness of planted forests in programs of species’ genetic resource conservation. In general, the genetic structure of the plantations was not strongly differentiated from the natural populations. For microsatellites, gene diversity (H) and allelic richness were significantly higher in plantations, while inbreeding was not different between planted and natural populations. For AFLPs, no significant difference was found between groups in the measures of genetic diversity. In the cluster analysis based on microsatellite data, plantations and natural populations from Santa Catarina State were grouped together, suggesting that plantations preserved genetic information very similar to natural populations. The cluster analysis of populations based on AFLP data differentiated plantations from natural populations. This pattern may be a result of genetic hitchhiking of AFLP fragments with genes under selective pressure due to plantations establishment and management. We suggest that the moderate to high level of genetic diversity retained in A. angustifolia populations after the intense fragmentation of the natural forest has the potential to supply plant material with sufficient genetic diversity for the species conservation through the establishment of planted forests. A sustainable management of the extant forest remnants and forestation/reforestation enterprises should additionally attend to trends revealed in previous studies concerning population structure and gene flow.     

Genetic differences between autochthonous and breeding populations of common cypress (Cupressus sempervirens L.) in Greece

Individuals were selected for resistance against the imperfect fungus Seiridium cardinale Wag in six common cypress populations (Cupressus sempervirens L.) in Greece. A total of 109 resistant clones and 140 trees from their base populations were surveyed at several allozyme loci. The comparison yielded information on changes in genetic variation due to artificial selection. The genetic structure of the breeding populations was similar to their base populations. Nevertheless, the number of rare alleles among the resistant clones had decreased, showing a similar trend at most loci and for most comparisons. Possible implications for breeding strategies are discussed.     

Genetic diversity of Populus euphratica populations in northwestern China determined by RAPD DNA analysis

Five Populus euphratica Oliver populations in northwestern China were analyzed using RAPD DNA markers to determine genetic diversity among and within populations. One hundred-and-five polymorphic bands were observed, ranging in size from 250 bp to 1700 bp, using 10 primers. Only one population on the north side of the Tianshern Range had a unique band common to all individuals that was not found in individuals from populations in the Tarim River valley. Intra-population genetic diversity was high in two populations along the Tarim River and low in the other three populations. There was no significant correlation between genetic distances and geographic distances. The result of correspondence analysis shows that the individuals from the three populations with low genetic diversity are isolated from each other. The result of cluster analysis based on genetic distance shows that the population in the Tianshern Range is genetically distant from the other populations. These results suggest that the Tianshern Range population was genetically isolated from the other populations.     

Seiridium cardinale on Juniperus species in Greece

Seiridium cardinale, the cause of cypress canker disease, was found on Juniperus foetidissima, J. excelsa, J. oxycedrus and J. phoenicea, in a number of natural juniper woodlands in Greece. The presence of infections was sporadic in most cases, with a limited number of plants affected by the pathogen. At one locality in the Prespes Lakes region of northern Greece, however, the incidence of infection was very high, especially on J. foetidissima and J. excelsa. The identity of S. cardinale was confirmed using morphological characters and comparisons of DNA sequences for the β‐tubulin gene region. The pathogenicity of S. cardinale isolates from Juniperus and Cupressus was verified in cross‐inoculation trials on both potted and field grown plants.     

The Eucalyptus stem canker pathogen Teratosphaeria gauchensis represents distinct genetic groups in Africa and South America

Teratosphaeria gauchensis (Capnodiales) causes a serious stem canker disease on commercially propagated Eucalyptus species in South America. Recently, this pathogen was detected for the first time in Africa. Very little is known regarding the biology or origin of T. gauchensis, but it has been suggested that it is native to South America. The aim of this study was to compare isolates from Africa and South America using microsatellite markers. Bayesian analysis conducted in STRUCTURE, principal coordinates analysis and a UPGMA dendrogram revealed two distinct genetic groups for these isolates. The South American isolates were more genetically diverse than those from Africa. Patterns of genetic diversity in Africa suggest that T. gauchensis could have been introduced into Zimbabwe before spreading north‐eastwards. The existence of the two genetic groups and high haplotype richness associated with the South American and Zimbabwean populations suggest that it will be more difficult to reduce the impact of disease caused by T. gauchensis in these regions than in those areas where there is limited genetic diversity.     

Spatial genetic structure in populations of the green oak leaf roller, Tortrix viridana L. (Lepidoptera, Tortricidae)

The green oak leaf roller (Tortrix viridana L.) is a major pest on oaks. The green oak leaf roller is one reason within a disease complex for the oak decline, and it leads to defoliation of oaks in spring. In Germany, Quercus robur L. is mainly affected. The partitioning of genetic variation within and among populations of forest pests is linked to their capacities for migration. And the capacity for migration is the basis for dispersal of the pest species to different host trees and host populations and, therefore, for further outbreak events. Thus, the within population spatial genetic structure (SGS) of T. viridana was investigated based on nuclear (AFLP) markers to analyse the dispersal capacity of this insect pest species at a very small spatial scale. A total of 401 individuals of the green oak leaf roller from four stands in North Rhine-Westphalia (Western Germany) were examined. In three of four populations, the AFLP markers revealed clearly SGS up to 40 m, which can be explained by the mating behaviour within this species.     

Genetic analysis and conservation of endangered medicinal tree species <Emphasis Type="Italic">Taxus wallichiana</Emphasis> in the Himalayan region

Taxus wallichiana is one of the most important medicinal tree species of the Himalayan region. Leaf and bark of the species yield an important drug called taxol, which is used for treatment of many types of cancer. There is a serious threat to the existence of the species due to over exploitation in its native habitat. Adequate information on the nature and the extent of genetic diversity in this important species is required for developing suitable strategy for its conservation. Random amplified polymorphic DNA (RAPD) and amplified fragment length polymorphism (AFLP) were used to assess genetic variation in nine natural populations of T. wallichiana from western part of the Himalayan ranges. Both the markers revealed low genetic diversity in these populations. Average heterozygosity for AFLP and RAPD were 0.3715 and 0.3072, respectively. Φ_ST values derived from molecular variance were 0.0855 and 0.1005 for AFLP and RAPD, respectively, whereas the corresponding G_ST values were 0.1796 and 0.2140. Most part of the genetic variation was present within the populations. However, between population variation was low but statistically significant, which suggested that the sampled populations might not constitute a single panmictic population. Cluster analysis and Mantel’s correlation revealed that genetic differentiation broadly followed geographic distribution of the populations. T. wallichiana thus urgently needs to be conserved using both in situ and ex situ conservation approaches.     

Factors shaping genetic structure within populations ofEurya japonica (Theaceae)

Starch-gel electrophoresis was used to resolve nine polymorphic enzyme loci from leaf tissue collected from 20 Korean populations ofEurya japonica in order to determine differences in allele frequencies between male and female trees. In addition, 84 adults were sampled and mapped in a population located on Naenaro Island in Korea to examine spatial genetic structure using spatial autocorrelation analysis. Allele frequencies between males and females gave few contribution to the genetic structuring within populations. Only nine (5%) of 180 cases were significantly different from both sexes in allele frequencies. On the other hand, Moran'sI was significantly different from the expected value in 31 (23.5%) of 132 cases. In the shortest distance (0<5m),I was significantly positive in 10 (22.7%) of 44 cases. The results indicate that a significant small scale genetic structure was detected in the population and patch widths were inferred to be approximately 5–7 m. A nonrandom distribution of genotypes may be indicative of restricted gene flowvia seed and pollen dispersal, and patchy establishments of genetically distinct individuals. These factors are responsible for shaping population genetic structure ofE. japonica.     

The ecology of fungal cankers on Cupressus macrocarpa in southern England

Bark isolations from cankers on Cupressus macrocarpa in southern England yielded Seiridium cardinale, Pestalotiopsis funerea and Pestalotiopsis monochaetioides. The recovery pattern of the three fungi indicated that only S. cardinale was a primary pathogen; the two Pestalotiopsis species being secondary. Pathogenicity data obtained following the inoculation of C. macrocarpa branches with mycelium of the three fungi confirmed this view. No evidence of vegetative incompatibility was found in S. cardinale, but five vegetative-compatibility (vc) groups were found in P. funerea and six in P. monochaetioides. Different vc groups of the two Pestalatiopsis species were often found in the same S. cardinale lesion, suggesting that a number of separate colonization events were involved. It is possible that this sometimes leads to complete replacement of the pathogen.     

Selection of a seed orchard of Eucalyptus dunnii based on genetic diversity criteria calculated using molecular markers

A Eucalyptus dunnii Maiden breeding population of 46 accessions originated in Australia and selected for fitness to subtropical and cold environments was screened by Amplified Fragment Length Polymorphism (AFLP) and microsatellite markers to obtain quantitative estimates of genetic diversity. A randomly chosen group of AFLP primers generated 205 AFLP bands that were used to fingerprint the genotypes and to evaluate genetic relationships among accessions. Sixty-eight percent (140) of the bands were polymorphic markers. The mean diversity index (DI) was 0.33 and about 52% of the loci had values greater than 0.4. Cluster analysis derived from similarity indices (SI) revealed no particular grouping among accessions suggesting the absence of closely related genotypes, except for five pairs of genotypes. Bootstrap analysis results confirmed the suitability of AFLP to describe genetic relationships in this breeding population. In addition, four highly informative microsatellites were used to construct an identification matrix that discriminated nearly all of the genotypes. Mean values for the number of alleles per locus, DI and SI among accessions were 13, 0.78 and 0.19, respectively, indicating that the breeding population has high genetic diversity. However, several genotypes showed the presence of single microsatellite bands suggesting a putatively important degree of homozygosity. Molecular data were used to design a clonal seed orchard. To achieve this aim, the nine most divergent pairs of genotypes were chosen, thereby retaining 95.2% of the total number of alleles from the 140 polymorphic AFLP loci and the four microsatellite loci analyzed. Mean DI and SI for AFLP and microsatellites showed no significant differences between the original breeding population and the selected seed orchard, confirming that a seed orchard can be designed with a limited number of individuals, which allows similar accessions to be discarded and avoids inbreeding.     

Biogeography of neutral genes and recent evolutionary history of pines in the Mediterranean Basin

Context

Mediterranean pines share many common life-history traits. They are found at almost all altitudinal levels around the Mediterranean Basin, from sea level to high-elevation mountains, and from hot and dry to wet and cold bioclimates. Their distribution ranges from widespread to regional and narrow, and from dense extensive populations to small populations of scattered individuals. They have been extensively used by human civilizations for millennia.

Aims

I show which are the main phylogenetic, ecological, and climatic factors explaining the patterns of within and among-population genetic diversity in Mediterranean pines.

Methods

I use a narrative synthesis approach and multiple examples from the literature on pine species from the Mediterranean Basin and California.

Results

While Mediterranean pines have the highest levels of differentiation worldwide, their genetic diversity increases from west to east and is significantly reduced in low-elevation species. Factors such as ancestral adaptation to wildfire, reduction of effective population size during the Last Glacial Maximum, long distance dispersal during the Holocene, and more recent adaptation to patchy environmental conditions could explain these patterns.

Conclusion

Because of contrasted ecological, demographic, historical, and geographical processes, and despite their common biological attributes, pines of the Mediterranean Basin display complex biogeographic patterns at neutral gene level that can help retrace their evolutionary history. Although individual species often represent unique case studies that make generalizations risky, locating habitats of significantly high and low genetic diversity is key for detecting and understanding the major factors affecting gene diversity and may prove useful for profiling areas of high conservation value in the Mediterranean.     

Pathogenic variation of Seiridium spp. isolated from cankered Cuppressaceae hosts in New Zealand

Field and glasshouse inoculation tests with isolates of S. cardinale and S. unicorne (Cke & Ell.) Sutton on C. macrocarpa and C lusitanien showed symptoms caused by the two pathogens to be indistinguishable. Isolates of S. cardinale showed an overall higher pathogenicity and less variability than those of S. unicorne. Neither pathogen seemed capable of infecting hosts outside the Cupressaceae, An isolate of Boesewinkel originating from Crvptowcria and supposed to be a distinct species from the anamorph of Lepteutypa cupressi, failea to infect Cryptomeria; neither could L. cupressi and S. cardinale, though all of them readily infected C. macrocarpa and C. lusitanica. Isolates of S. unicoene showed vast differences in pathogenicity in any one test, but many of the Isolates also showed extremi pathogenicity variation between repeat tests, hence pathogenicity determination became uncertain or probalistic. There is no evidence that the decline of S cardinale in this country is due to reduced pathogenicity or to possible interaction with S. unicorne in host infection.     

Genetic diversity of apple‐ and crabapple‐infecting isolates of Venturia inaequalis in Pennsylvania,the United States,determined by microsatellite markers

Apple scab caused by Venturia inaequalis is the most destructive disease of apple worldwide. In this study, genetic diversity of 101 V. inaequalis isolates from cultivated apples and ornamental crabapples in Pennsylvania (PA, USA) was characterized using 14 microsatellite markers. A total of 157 alleles ranging from 5 (Vitg9/99) to 26 (Vica10/154) per locus were detected. Regardless of the host of origin, isolates were grouped into five clusters, which were largely supported by STRUCTURE and principal coordinate analysis. Cluster analyses based on genetic distances and population structure analysis suggest very small differentiation (PhiPT ranging from 0.016 to 0.103, depending on the population comparison) between apple and crabapple isolates of V. inaequalis. Pairwise comparisons among populations from different locations showed very low differentiation, and POPGENE analysis indicated frequent migration of alleles (Nm = 1.47). In pathogenicity tests using a detached leaf assay, isolates of V. inaequalis from crabapple caused characteristic scab symptoms on apple and were highly virulent. Results of the study indicate that scab lesions in crabapple trees in close vicinity to apple orchards could serve as reservoirs for spread of the pathogen. Movement of inoculum among locations and between hosts may be responsible for the limited population structure observed. Understanding the population structure of V. inaequalis isolates is significant for apple scab management as crabapples are often used as pollinizers and rootstock in apple orchards, and as ornamental trees.     

AFLP analysis of genetic variation of Hyphantria cunea (Drury) populations in Beijing and a nearby site

Hyphantria cunea (Drury) is a severe invasive pest in Beijing. It is important to understand the reason for its successful invasion and outbreak. Accordingly, this study was tailored to assess molecular variation and genetic relationships among three H. cunea populations in Beijing and one population from Sanhe in Hebei Province as control (totally 100 individuals). A silver-labeled amplified fragment length polymorphisms (AFLP) DNA profiling method was used to detect the genetic diversity and relationship among the populations. Five EcoRI and MseI primer combinations produced a total of 171 (91.2% polymorphic) informative fragments. The average Nei’s genetic diversity in four H. cunea populations analyzed by Popgene3.2 software was 0.2287, and the level of genetic diversity ranked in the order BDR (reared population in Daxing, Beijing) > BDN (natural population in Daxing, Beijing) > HSN (natural population in Sanhe, Hebei Province) > BFN (natural population in Fengtai, Beijing). The value of genetic differentiation among populations was 0.3321, and the gene flow was 1.0057. The genetic distance between these populations ranged from 0.0735 to 0.3309, 0.0531 on average. The result of UPGMA (unweighed pair group method with arithmetic averages) clustering showed that populations BFN and HSN were closely related, while BFN and BDN had the largest genetic distance. These results indicate that H. cunea populations in Beijing might originate from several areas.     

Trichoderma viride on cypress shoots and antagonistic action against Seiridium cardinale

The recovery of Trichoderma viride from shoots of Cupressus sempervirens L. in different localities of Northern Italy and its antagonistic action against Seiridium cardinale, agent of the cypress canker, are described.     

Responses of Cupressus and Chamaecyparis callus tissues to inoculations with Seiridium cardinale

Inoculations of callus generated from micropropagated shoots of Cupressus sempervirens, Cupressus macrocarpa, Cupressus torulosa and Chamaecyparis lawsoniana showed that callus of species resistant or relatively resistant to Seiridium cardinale supported significantly less surface growth of the pathogen than callus of susceptible species. In dual cultures of Cupressus sempervirens or Cupressus torulosa callus with S. cardinale, inhibition of fungal growth towards the callus was correlated with known field resistance of these host species. Lignification, accumulation of polyphenolics and possible suberization of cell walls were detected in inoculated callus. This response was also correlated with known field resistance of the tested host species.     

10个南方皂荚群体遗传多样性的AFLP分析

[目的]研究南方皂荚的遗传多样性和遗传结构现状,为制定有效的保护策略和育种策略提供理论依据。[方法]采用扩增片段长度多态性技术对供试的215份皂荚的遗传多样性及遗传距离进行分析。[结果]表明:检测到1 782个位点,其中,有1 389个为多态性位点,多态位点百分率为77.94%;皂荚各群体Shannon’s信息指数平均为0.256;Nei’s多样性指数平均为0.168,表明皂荚群体的遗传多样性偏低,皂荚群体间存在着一定的遗传分化;根据遗传距离UPGMA聚类分析,将10个群体划分为4大类。由遗传分化系数和分子方差分析结果发现,群体内的变异是皂荚遗传变异的主体,74.79%的变异来自群体内。[结论]皂荚群体的遗传多样性与遗传结构的形成不仅与其分布广泛、种子特性及生活史有关,而且与人为的砍伐、引种、生境片段化等因素有重要关系。基于上述结果提出了皂荚的保护策略。     

Seiridium cardinale cankers in a tolerant Cupressus sempervirens clone under naturally CO2‐enriched conditions

Ramets of the Cupressus sempervirens clone Bolgheri were raised in three CO₂ concentrations in a naturally CO₂‐enriched environment [360 (control), 680 and 1670 μmol mol^–1 CO₂]. Bolgheri is patented as resistant to Seiridium cardinale. The ramets were artificially inoculated using a virulent isolate of S. cardinale. Healing of the resulting cankers was visually assessed over 6 years. Six months after inoculation, cankers on trees grown at 680 μmol mol^–1 were significantly larger than the controls. However, no significant trend was recorded at later dates. In conclusion, the Bolgheri clone maintained its resistance to S. cardinale and could be used to control cypress canker even in increasing atmospheric CO₂ concentrations.