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The genetic diversity and growth dynamics of fifty-three half-sib families of eleven provenance sources and one bulk seed mixed population of fast growing forest tree species i.e. Melia azedarach were studied at two stand ages viz., fourth year (mid-rotation) and eighth year (end-rotation) to determine the selection stage in northern India. Significant variations were reported between and within seed provenances in all growth characters at both rotational ages. The broad sense heritability was higher at mid-rotational age. This revealed the growth is genetically controlled but with the time environmental effects escort the growth pattern. Growth pattern was different at each stand age. Growth is diameter dependent and the pattern was crown growth type. Families maintained their superiority over the time for tree height, basal diameter and diameter at breast height, which indicated a strong potential to identify good performing families for future plantation program. This study concluded that early stage selection is appropriate that later stage selection for all parameters studied except clear bole height that is much influenced by management practice and environment factors also. Neighbor-joining clustering with similarity index revealed that it is not necessary that the families, originated in one region were distributed in one cluster, indicating that families with same geographic origin could have undergone changes for different characters under selection. [ABSTRACT FROM AUTHOR]

Aims Exploring species-genetic diversity correlation (SGDC) is essential for understanding spatial patterns of diversity and the underlying mechanisms. Until now, latitudinal patterns of species diversity (SD) and genetic diversity (GD) were rarely studied simultaneously. As the freezing-tolerance hypothesis predicts a decrease of SD from low to high latitudes and the central-marginal hypothesis predicts a unimodal pattern of GD along latitude, we hypothesized that SD and GD are uncorrelated. We also tested how climatic and edaphic factors affect the correlation between the two levels of biodiversity. Methods We measured (i) SD (species richness and Simpson's diversity index) and community dissimilarity of woody plants (63 plots), (ii) GD (allelic richness and expected heterozygosity) and genetic differentiation of a dominant tree species (Euptelea pleiospermum ; 678 individuals from 21 populations) using nuclear microsatellite data, and (iii) climatic (annual mean precipitation, annual mean temperature, minimum temperature, maximum temperature, annual relative moisture, solar radiation, photosynthetically active radiation) and edaphic (total C, total N, total P, available P, K, Ca, Mg, Al, Fe, Mn, Ni, Zn, B, Mo, Cu, pH) variables of 21 sites. We conducted both linear and quadratic regression analyses of diversity parameters against latitude. Relationships between SD and GD were tested using Pearson's correlation. Pearson's and Spearman's ρ correlation coefficients were calculated between diversity parameters and environmental variables. We used stepwise multiple regression analysis to identify the significant environmental predictors of SD and GD. Important Findings We observed no significant correlation between measures of SD and GD. SD decreases with increasing latitude, which can be partly explained by the freezing-tolerance hypothesis, whereas GD presents a unimodal pattern along the latitudinal gradient, which is consistent with the prediction of the central-marginal hypothesis. The contrasting latitudinal patterns of SD and GD indicate that the two levels of biodiversity do not co-vary in space. Based on both correlation analysis and stepwise multiple regression analysis, SD is only related to climatic variables, whereas GD is mainly related to edaphic variables. Our results show that different geographical and environmental factors affect SD and GD, driving the non-significant correlation between the two fundamental levels of biodiversity. Furthermore, a significantly positive correlation was observed between genetic distance and community dissimilarity, both of which were significantly correlated with geographical distance. [ABSTRACT FROM AUTHOR]

Gene flow is one of the main factors shaping genetic diversity within and among tree populations, and occurs through pollen and seed dispersal. Recent findings of pollen-release asynchronies in distant populations of Scots pine (Pinus sylvestris L.) within Scotland suggest that gene dispersal among more distant populations might be less effective than previously thought. Limited gene dispersal is one of the major factors causing genetic structure for neutral markers, and pollen-release asynchrony could have driven isolation by distance (IBD) among Scottish populations. Previous studies of neutral markers found little differentiation among Scottish populations of Scots pine, however they did not consider IBD over the full Scottish range. We analysed data from 6 nuclear simple sequence repeats (SSR) and 5 chloroplast SSR loci in a total of 540 individuals of Scots pine from 18 populations across Scotland. Our aim was to assess contemporary levels and distribution of genetic variation and to test if the distribution of genetic diversity was consistent with IBD. We also analysed patterns of gene flow that could have contributed to the observed patterns of variation. Levels of genetic diversity were high, for both nuclear and chloroplast markers within populations, and there was no significant differentiation among populations. A weak signal of IBD was present. We found an increase in nuclear diversity towards the East along with greater gene flow in a West-East direction commensurate with the prevailing winds. Our findings suggest that this wind-driven gene flow is dominant over genetic drift and prevents differentiation among the Scottish populations. It may also counteract any pollen-release asynchronies among populations. [ABSTRACT FROM AUTHOR]

Garry oak ( Quercus garryana Douglas ex Hook.) is a deciduous tree whose ecosystem is listed 'at risk' throughout its range in British Columbia (BC), Canada, under the Canadian Species at Risk Act. Garry oak ecosystems host the most diverse flora for coastal BC, yet they account for less than 0.3% of the province's land coverage. Due to the loss and degradation of Garry oak habitat, many associated plant and animal species that rely on these sensitive ecosystems are endangered. Microsatellite markers were used to investigate temporal changes in fine-scale population genetic structure of 121 Garry oak trees from the Nanaimo region (Vancouver Island, BC) using diameter at breast height as a proxy for age. Overall, allelic diversity was moderate, ranging from 3.0 to 7.5 alleles per locus with a mean of 4.4 (±0.4 SE) across all loci. Global fixation indices ( FST) of 0.06 and 0.09 suggest significant departures from Hardy-Weinberg equilibrium among all populations and age-classified subpopulations, respectively. We found no evidence for change in genetic diversity across generations. Our results indicate low levels of differentiation within populations and high levels of gene flow among populations, suggesting an adaptive potential for Garry oaks in response to future climate change events. [ABSTRACT FROM AUTHOR]

Like many other high elevation alpine tree species, Rocky Mountain bristlecone pine (Pinus aristata Engelm.) may be particularly vulnerable to climate change. To evaluate its potential vulnerability to shifts in climate, we defined the suitable climate space for each of four genetic lineages of bristlecone pine and for other subalpine tree species in close proximity to bristlecone pine forests. Measuring changes in the suitable climate space for lineage groups is an important step beyond models that assume species are genetically homogenous. The suitable climate space for bristlecone pine in the year 2090 is projected to decline by 74% and the proportional distribution of suitable climate space for genetic lineages shifts toward those associated with warmer and wetter conditions. The 2090 climate space for bristlecone pine exhibits a bimodal distribution along an elevation gradient, presumably due to the persistence of the climate space in the Southern Rocky Mountains and exclusion at mid-elevations by conditions that favor the climate space of other species. These shifts have implications for changes in fire regimes, vulnerability to pest and pathogens, and altered carbon dynamics across the southern Rockies, which may reduce the likelihood of bristlecone pine trees achieving exceptional longevity in the future. The persistence and expansion of climate space for southern bristlecone pine genetic lineage groups in 2090 suggests that these sources may be the least vulnerable in the future. While these lineages may be more likely to persist and therefore present opportunities for proactive management (e.g., assisted migration) to maintain subalpine forest ecosystem services in a warmer world, our findings also imply heighted conservation concern for vulnerable northern lineages facing range contractions. [ABSTRACT FROM AUTHOR]

During Quaternary glaciations, the ranges of Northern Eurasia forest species periodically experienced contraction followed by subsequent re-colonizations in the interglacial intervals. However, unlike the broadleaf trees of temperate forests, taiga species seem not to have retreated fully to southern regions in unfavorable periods and possibly survived at mid-latitudes in multiple refugia. Here, we report a study of genetic variation of three mitochondrial DNA markers in 90 populations of Scots pine ( Pinus sylvestris) located from Eastern Europe to Eastern Siberia. The geographic distribution of seven mitotypes demonstrated the split between western and eastern populations approximately along the 38th meridian. Genetic diversity in the western part was significantly higher than in the eastern one. Five mitotypes were western- and one eastern-specific. One mitotype was common in both regions, but in the eastern part it occurred only in the South Urals and adjacent areas. The geographic structure in the mitotype distribution supports a hypothesis of post-glacial re-colonization of the studied territory from the European and Ural refugia. [ABSTRACT FROM AUTHOR]

Understanding patterns of genetic diversity at the landscape scale will enhance conservation and management of natural populations. Here we analyzed the genetic diversity, population connectivity, and spatial genetic structure among subpopulations and age groups of Olea europaea subsp. cuspidata, a cornerstone species of the Afromontane highlands. The study was conducted at the landscape level within a radius of approximately 4 km, as well as on a fine scale (intensive study plot) of less than 300 m radius. In total 542 samples from four natural subpopulations in northwestern Ethiopia were analyzed using ten nuclear microsatellite markers. Inbreeding was higher in smaller populations. No genetic difference was detected among cohorts of different tree sizes in the intensive studied plot. Average population differentiation was low but significant ( F = 0.016). Landscape genetic analysis inferred two groups: the most distant subpopulation WE located less than 4 kms from the other three subpopulations formed a separate group. Sixty-four percent of the total migrants were shared among the three latter subpopulations, which are spatially clustered. Immigrants were non-randomly distributed inside of the intensive study plot. Significant spatial genetic structure (SGS) was found both at the landscape scale and in the intensive study plot, and adults showed stronger SGS than young trees. An indirect estimate of 220 m as mean gene dispersal distance was obtained. We conclude that even under fragmentation migration is not disrupted in wild olive trees and that large protected populations at church forests are very important to conserve genetic resources. However, the higher level of inbreeding and evidence for population bottlenecks in the small populations, as well as the persisting heavy pressure on most remaining populations, warrants quick action to maintain genetic diversity of wild olive in the Ethiopian highlands. [ABSTRACT FROM AUTHOR]

Globally, alpine treelines are characterized as temperature-limited environments with strong controls on tree growth. However, at local scales spatially heterogeneous environments generally have more variable impacts on individual patterns of tree growth. In addition to the landscape spatial heterogeneity there is local variability in individual tree genetic diversity (level of individual heterozygosity). It has been hypothesized that higher individual heterozygosity will result in more consistent patterns of growth. In this article, we combine genomics and dendrochronology to explore the relationship between individual genetic diversity and tree growth at a mountain hemlock (Tsuga mertensiana Bong. Carr) alpine treeline on the Kenai Peninsula, Alaska, USA.We correlated average observed individual heterozygosity with average tree-ring width and variance in tree-ring width within individuals to test the hypothesis that trees with higher individual heterozygosity will also have more consistent growth patterns, suggesting that they may be more resilient to climate and environmental fluctuations at the alpine treeline. Our results showed that there was no significant relationship between tree growth and individual heterozygosity. However, there was a significant positive relationship between average tree-ring width and variance in tree-ring width implying that overall, fast growing trees in stressful environments, such as the alpine treeline, grow unstably regardless of the level of individual heterozygosity. [ABSTRACT FROM AUTHOR]

Accurate inference of relatedness between individuals in breeding population contributes to the precision of genetic parameter estimates, effectiveness of inbreeding management and the amount of genetic progress delivered from breeding programs. Pedigree reconstruction has been proven to be an efficient tool to correct pedigree errors and recover hidden relatedness in open pollinated progeny tests but the method can be limited by the lack of parental genotypes and the high proportion of alien pollen from outside the breeding population. Our study investigates the efficiency of sib-ship reconstruction in an advanced breeding population of Eucalyptus nitens with only partially tracked pedigree. The sib-ship reconstruction allowed the identification of selfs (4% of the sample) and the exploration of their potential effect on inbreeding depression in the traits studied. We detected signs of inbreeding depression in diameter at breast height and growth strain while no indications were observed in wood density, wood stiffness and tangential air-dry shrinkage. After the application of a corrected sib-ship relationship matrix, additive genetic variance and heritability were observed to increase where signs of inbreeding depression were initially detected. Conversely, the same genetic parameters for traits that appeared to be free of inbreeding depression decreased in size. It therefore appeared that greater genetic variance may be due, at least in part, to contributions from inbreeding in these studied populations rather than a removal of inbreeding as is traditionally thought. [ABSTRACT FROM AUTHOR]

Whitebark pine (WBP, Pinus albicaulis Engelm.) is an endangered conifer species due to heavy mortality from white pine blister rust (WPBR, caused by Cronartium ribicola) and mountain pine beetle (Dendroctonus ponderosae). Information about genetic diversity and population structure is of fundamental importance for its conservation and restoration. However, current knowledge on the genetic constitution and genomic variation is still limited for WBP. In this study, an integrated genomics approach was applied to characterize seed collections from WBP breeding programs in western North America. RNA-seq analysis was used for de novo assembly of the WBP needle transcriptome, which contains 97,447 protein-coding transcripts. Within the transcriptome, single nucleotide polymorphisms (SNPs) were discovered, and more than 22,000 of them were non-synonymous SNPs (ns-SNPs). Following the annotation of genes with ns-SNPs, 216 ns-SNPs within candidate genes with putative functions in disease resistance and plant defense were selected to design SNP arrays for high-throughput genotyping. Among these SNP loci, 71 were highly polymorphic, with sufficient variation to identify a unique genotype for each of the 371 individuals originating from British Columbia (Canada), Oregon and Washington (USA). A clear genetic differentiation was evident among seed families. Analyses of genetic spatial patterns revealed varying degrees of diversity and the existence of several genetic subgroups in the WBP breeding populations. Genetic components were associated with geographic variables and phenotypic rating of WPBR disease severity across landscapes, which may facilitate further identification of WBP genotypes and gene alleles contributing to local adaptation and quantitative resistance to WPBR. The WBP genomic resources developed here provide an invaluable tool for further studies and for exploitation and utilization of the genetic diversity preserved within this endangered conifer and other five-needle pines. [ABSTRACT FROM AUTHOR]

During post glacial colonization, loss of genetic diversity due to leading edge effects may be attenuated in forest trees because of their prolonged juvenile phase, allowing many migrants to reach the colonizing front before populations become reproductive. The northern range margins of temperate tree taxa in Europe are particularly suitable to study the genetic processes that follow colonization because they have been little affected by northern refugia. Here we examined how post glacial range dynamics have shaped the genetic structure of common ash (Fraxinus excelsior L.) in its northern range compared to its central range in Europe. We used four chloroplast and six nuclear microsatellites to screen 42 populations (1099 trees), half of which corresponded to newly sampled populations in the northern range and half of which represented reference populations from the central range obtained from previously studies. We found that northern range populations of common ash have the same chloroplast haplotypes as south-eastern European populations, suggesting that colonization of the northern range took place along a single migration route, a result confirmed by the structure at the nuclear microsatellites. Along this route, diversity strongly decreased only in the northern range, concomitantly with increasing population differentiation and complex population substructures, a pattern consistent with a leading edge colonization model. Our study highlights that while diversity is maintained in the central range of common ash due to broad colonizing fronts and high levels of gene flow, it profoundly decreases in the northern range, where colonization was unidirectional and probably involved repeated founder events and population fluctuations. Currently, common ash is threatened by ash dieback, and our results on northern populations will be valuable for developing gene conservation strategies. [ABSTRACT FROM AUTHOR]

Accurate prediction of genetic potential and response to selection in breeding requires knowledge of genetic parameters for important selection traits. In this study, we estimated genetic parameters for wood properties in Khasi pine (Pinus kesiya Royle ex Gordon) grown in Malawi. Data on wood properties and growth traits were collected from six families of Pinus kesiya at the age of 30. The results show that wood density had a higher genetic control (h2 = 0.595 ± 0.055) than wood stiffness (h2 = 0.559 ± 0.038) and wood strength (h2 = 0.542 ± 0.091). The genetic correlation among wood quality traits was significantly moderate (0.464 ± 0.061) to high (0.735 ± 0.025). The predicted genetic response indicated that selection for wood density at 10% selection intensity would increase stiffness and strength by 12.6% and 8.85%, respectively. The genetic correlations between growth and wood quality traits were moderately unfavourable. However, sufficient variation exists within the breeding population to select individuals with both good growth rate and high wood quality traits. It is therefore suggested that all trees with both diameter at breast height (DBH) greater than 32.0 cm and density greater than 0.593 g/cm3 must be selected in order to increase the efficiency of the breeding programme. However, in the long term, it is recommended that the best selection strategy would be to develop a multiple-trait selection index. The selection index should be developed using optimal index weights for the advanced Pinus kesiya breeding programme in Malawi. [ABSTRACT FROM AUTHOR]

Mangrove forests of Mexico have been threatened by the effects of anthropogenic activities during the last decades, mostly related to aquaculture, agriculture, livestock and urban development. Genetic diversity and fine-scale genetic structure of two generations of the black mangrove Avicennia germinans (L.) Stearn were investigated in perturbed and preserved sites from three lagoon systems in Sinaloa, Mexico. Genetic diversity and overall genetic structure were similar between perturbed and preserved sites. However, lower levels of fine-scale spatial genetic structure were observed in two of the younger (sapling) generations. We attribute this to differences in local dynamics of each lagoon system, their status of conservation and levels of fragmentation. Also, low connectivity and the effects of disturbance could restrict the movement of pollinators and seed dispersal capabilities, resulting in low levels of genetic diversity and signs of inbreeding. Perturbed populations of A. germinans may play an important role in in situ conservation of this complex ecosystem. [ABSTRACT FROM AUTHOR]

Sequoia sempervirens (Coast redwood (Lamb. ex D. Don) Endl.) plantings in New Zealand are increasing due to favourable growth rates. There is, however, very limited information on S. sempervirens genetics on which to build breeding and deployment decisions. In this study we present results from the assessment of growth, wood density, heartwood area, and epicormic shoots in two replicated clonal provenance trials of 170 S. sempervirens clones at two sites. Across-site genetic correlations among provenance for traits were high, 0.9 or above, with the exception of 0.7 for epicormic shoots. Medium-to-high genetic control was expressed for all growth and wood property traits. Broad-sense heritabilities for the two sites assessed were: diameter at breast height (1.4 m) (0.35 and 0.52), wood density (0.52 and 0.30), and percentage heartwood (0.40 and 0.50). Epicormic shoots were under low genetic control (0.11 and 0.27) and may be more influenced by the environment. Genetic correlations between traits showed that growth rate was negatively correlated with wood density (−0.52 to −0.58). Faster growth was also correlated with more epicormic shoots (0.36-0.44). We found no strong trends between growth performance, provenance location, or provenance site characteristics of the material tested. In contrast to earlier research in the United States of America, this study found a high clonal repeatability for the above traits and it demonstrated a low genotype × environment interaction. This study provides important and new insights in the genetic variability of S. sempervirens provenances. [ABSTRACT FROM AUTHOR]

Compared to natural selection, domestication implies a dramatic change in traits linked to fitness. A number of traits conferring fitness in the wild might be detrimental under domestication, and domesticated species typically differ from their ancestors in a set of traits known as the domestication syndrome. Specifically, trade-offs between growth and reproduction are well established across the tree of life. According to allocation theory, selection for growth rate is expected to indirectly alter life-history reproductive traits, diverting resources from reproduction to growth. Here we tested this hypothesis by examining the genetic change and correlated responses of reproductive traits as a result of selection for timber yield in the tree Pinus pinaster. Phenotypic selection was carried out in a natural population, and progenies from selected trees were compared with those of control trees in a common garden experiment. According to expectations, we detected a genetic change in important life-history traits due to selection. Specifically, threshold sizes for reproduction were much higher and reproductive investment relative to size significantly lower in the selected progenies just after a single artificial selection event. Our study helps to define the domestication syndrome in exploited forest trees and shows that changes affecting developmental pathways are relevant in domestication processes of long-lived plants. [ABSTRACT FROM AUTHOR]

Cork oak ( Quercus suber L.) is an evergreen tree species endemic to the western Mediterranean Basin with a major economical, social and ecological relevance, associated with cork extraction and exploitation. In the last years, cork oak stands have been facing a significant decline, which may be aggravated by the climate changes that are predicted to occur within cork oak distribution range during this century. Under this scenario, the assessment of adaptive genetic variation is essential to understand how cork oak may cope with these threats and to delineate strategies for the management of its genetic resources. In this study, six candidate genes possibly significant for environmental adaptation were analysed in cork oak populations from its entire distribution range. Signatures of natural selection were investigated using population genetic statistics and environmental association tests under alternative scenarios of population genetic structure. Signals of balancing selection were detected in the putative non-expressor of pathogenesis-related gene 1 ( NPR1), involved in plant defence response against pathogens, in auxin response factor 16 ( ARF16), a gene implicated in root development, in RAN3, also involved in developmental processes, and in glutamine synthetase nodule isozyme ( GS), involved in nitrogen fixation. Furthermore, for ARF16, a class I heat shock protein ( sHSP) and GS, associations were found between SNP allele and haplotype frequencies and several spatial and climatic variables, suggesting that these genes may have a role on cork oak local adaptation. In this study, the first steps were taken into gathering information on cork oak adaptation to environmental conditions. [ABSTRACT FROM AUTHOR]

The estimates of contemporary gene flow assessed based on naturally established seedlings provide information much needed for understanding the abilities of forest tree populations to persist under global changes through migration and/or adaptation facilitated by gene exchange among populations. Here, we investigated pollen- and seed-mediated gene flow in two mixed-oak forest stands (consisting of Quercus robur L. and Q. petraea [Matt.] Liebl.). The gene flow parameters were estimated based on microsatellite multilocus genotypes of seedlings and adults and their spatial locations within the sample plots using models that attempt to reconstruct the genealogy of the seedling cohorts. Pollen and seed dispersal were modelled using the standard seedling neighbourhood model and a modification—the 2-component seedling neighbourhood model, with the later allowing separation of the dispersal process into local and long-distance components. The 2-component model fitted the data substantially better than the standard model and provided estimates of mean seed and pollen dispersal distances accounting for long-distance propagule dispersal. The mean distance of effective pollen dispersal was found to be 298 and 463 m, depending on the stand, while the mean distance of effective seed dispersal was only 8.8 and 15.6 m, which is consistent with wind pollination and primarily seed dispersal by gravity in Quercus. Some differences observed between the two stands could be attributed to the differences in the stand structure of the adult populations and the existing understory vegetation. Such a mixture of relatively limited seed dispersal with occasional long distance gene flow seems to be an efficient strategy for colonizing new habitats with subsequent local adaptation, while maintaining genetic diversity within populations. [ABSTRACT FROM AUTHOR]

Forest trees have tremendous economic and ecological value, as well as unique biological properties of basic scientific interest. The inherent difficulties of experimenting on very large long-lived organisms motivates the development of a model system for forest trees. Populus (poplars, cottonwoods, aspens) has several advantages as a model system, including rapid growth, prolific sexual reproduction, ease of cloning, small genome, facile transgenesis, and tight coupling between physiological traits and biomass productivity. A combination of genetics and physiology is being used to understand the detailed mechanisms of forest tree growth and development. [ABSTRACT FROM AUTHOR]

The article focuses on the problems and potentials of tree growth control systems. It stresses on the need to increase tree growth, for meeting the rise in the need of forest products. It states that the forest lands in the U.S. is much below potential levels. The U.S. has begun agroforestry, an intensive culture of tree crops. It mentions that use of improved tree hybrids and knowledge of practical application of tree growth control, are implicit factors of agroforestry systems. It discusses the main problems related to agroforestry systems, that includes growth periodicity and its regulation. Physiology of tree growth is also described. It explains new methods of growth control, including genetics or breeding, culture and use of regulators.

Reports that Om Rajora of the University of New Brunswick has been awarded a federal support for a new Canada Research Chair. Credibility of Rajora for the job; Total amount allocated for the research funding; Aims of the study to explore the genetics basis of trees' productivity, health and ability to adapt to climate change.