Delivering material selected for breeding purposes into the wild in the context of sustainable forest management might reduce the levels of genetic diversity of future forests in comparison to that of natural populations. Another consequence might be a reduction of their resilience under uncertain future climatic and socio-economic conditions if these new populations lack adaptability. Despite the long tradition of breeding activities in Europe, there is still a need to assess the impact of genetically enriched material on forests’ resilience. In this study, we address (1) the genetic diversity of selected material compared to its wild ancestors, and (2) how to enrich breeding material to support forests’ resilience under changing socio-environmental conditions. We analysed 16 study cases of selected material delivered from breeding activities in four European forest tree species (Pinus halepensis Mill., Pinus nigra J.F. Arnold, Pinus pinaster Ait. and Populus nigra L.) with different levels of breeding. To answer these two questions, we first assessed and compared the genetic diversity of selected material versus natural populations using both putatively neutral and adaptive (based on diverging selection) Single Nucleotide Polymorphisms (SNPs). We then suggest how to enrich these populations for resilience under future climatic conditions by defining a core collection for each species including material from populations that will likely disappear under future conditions. Thanks to the large SNP datasets available for our focal species, we were able to detect some trends in our data. Expected and observed heterozygosity values for selected populations were almost always identical. The selected material showed small but significant genetic differentiation from their original population and their inbreeding coefficient was generally lower. However, the level of genetic improvement (i.e. low vs high) was not correlated with the observed genetic differences between selected material and natural populations.The genetic characterization of natural populations distributed across the species range, and the future projection of their range stability, made it possible to identify core-collections that would significantly enrich breeding populations under uncertain future environmental conditions.

The genetic monitoring of forest trees is of the utmost importance for securing the maintenance of species’ adaptive potential. Genetic monitoring, the quantification of temporal changes in a population’s genetic variation and structure, introduces prognosis and assists in defining tools for the management of genetic resources. Forest genetic monitoring (FGM) is imperative in biodiversity hotspots such as Greece, one of the most species-rich European countries, where >7000 native plant taxa (~20% endemics) exist and 28% of its land base is included in the Natura 2000 Special Areas of Conservation network. Moreover, (meta-)analyses of genetic data have shown that Greek forests’ tree populations present significantly higher values of polymorphism and differentiation compared to the average values reported in the international literature. FGM studies in Greece involve the following species: Abies borissi regis, Castanea sativa, Fagus sylvatica, Quercus petraea, Q. robur, Pinus nigra, and Prunus avium. FGM uses a genealogical approach and employs 11–26 Simple Sequence Repeat (SSR) loci in different cohorts (mature and juvenile trees), while the average time internal between assessments is 12.9 years. The results so far for A. borissi regis and F. sylvatica indicate a maintenance of genetic diversity over time, but with a slight drop of Ne in the juvenile cohort of hybrid firs compared to the mature trees.

Platanus orientalis L. var. cretica is the ever-growing mutant of Platanus orientalis L. (plane tree) and its population consists of few trees, growing in isolation on the island of Crete, in the Aegean Archipelago of Greece, while the typical plane tree form is ubiquitous to the island and mainly present in streams and ravines. In the present study, 23 mutant and adjacent typical plane tree pairs were studied. Four leaf morphometry parameters were measured using the ImageJ software in order to derive five independent of size leaf shape ratios. Paired comparisons using Kruskal-Wallis tests were conducted via the SPSS software. The analyses showed no general tendency of statistically significant differences regarding studied parameters between pairs. Statistically significant differences (p < 0.05) in the majority of the analyzed ratios were detected in 35% of the studied pairs. Our results show that the leaf morphometrics present notable phenotypic variation which can be valuable in diversity studies. Nevertheless, they are not particularly useful in distinguishing P. orientalis L. and the ever-growing P. orientalis L. var. cretica.

Motivation: Trait variation within species can reveal plastic and/or genetic responses to environmental gradients, and may indicate where local adaptation has occurred. Here, we present a dataset of rangewide variation in leaf traits from seven of the most ecologically and economically important tree species in Europe. Sample collection and trait assessment are embedded in the GenTree project (EU-Horizon 2020), which aims at characterizing the genetic and phenotypic variability of forest tree species to optimize the management and sustainable use of forest genetic resources. Our dataset captures substantial intra- and interspecific leaf phenotypic variability, and provides valuable information for studying the relationship between ecosystem func-tioning and trait variability of individuals, and the response and resilience of species to environmental changes. Main types of variable contained: We chose morphological and chemical characters linked to trade-offs between acquisition and conservation of resources and water use, namely specific leaf area, leaf size, carbon and nitrogen content and their ratio, and the isotopic signature of stable isotope 13C and 15N in leaves. Spatial location and grain: We surveyed between 18 and 22 populations per species, 141 in total, across Europe. Time period: Leaf sampling took place between 2016 and 2017. Major taxa and level of measurement: We sampled at least 25 individuals in each population, 3,569 trees in total, and measured traits in 35,755 leaves from seven European tree species, i.e. the conifers Picea abies, Pinus pinaster and Pinus sylvestris, and the broadleaves Betula pendula, Fagus sylvatica, Populus nigra and Quercus petraea. Software format: The data files are in ASCII text, tab delimited, not compressed.

Background: Progress in the field of evolutionary forest ecology has been hampered by the huge challenge of phenotyping trees across their ranges in their natural environments, and the limitation in high-resolution environmental information. Findings: The GenTree Platform contains phenotypic and environmental data from 4,959 trees from 12 ecologically and economically important European forest tree species: Abies alba Mill. (silver fir), Betula pendula Roth. (silver birch), Fagus sylvatica L. (European beech), Picea abies (L.) H. Karst (Norway spruce), Pinus cembra L. (Swiss stone pine), Pinus halepensis Mill. (Aleppo pine), Pinus nigra Arnold (European black pine), Pinus pinaster Aiton (maritime pine), Pinus sylvestris L. (Scots pine), Populus nigra L. (European black poplar), Taxus baccata L. (English yew), and Quercus petraea (Matt.) Liebl. (sessile oak). Phenotypic (height, diameter at breast height, crown size, bark thickness, biomass, straightness, forking, branch angle, fructification), regeneration, environmental in situ measurements (soil depth, vegetation cover, competition indices), and environmental modeling data extracted by using bilinear interpolation accounting for surrounding conditions of each tree (precipitation, temperature, insolation, drought indices) were obtained from trees in 194 sites covering the species' geographic ranges and reflecting local environmental gradients. Conclusion: The GenTree Platform is a new resource for investigating ecological and evolutionary processes in forest trees. The coherent phenotyping and environmental characterization across 12 species in their European ranges allow for a wide range of analyses from forest ecologists, conservationists, and macro-ecologists. Also, the data here presented can be linked to the GenTree Dendroecological collection, the GenTree Leaf Trait collection, and the GenTree Genomic collection presented elsewhere, which together build the largest evolutionary forest ecology data collection available.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Sweet cherries, Prunus avium L. ( Rosaceae ), are gaining importance due to their perenniallity and nutritional attributes beneficial for human health. Interestingly, sweet cherry cultivars exhibit a wide range of phenotypic diversity in important agronomic traits, such as flowering time and defense reactions against pathogens. In this study, whole-genome resequencing (WGRS) was employed to characterize genetic variation, population structure and allelic variants in a panel of 20 sweet cherry and one wild cherry genotypes, embodying the majority of cultivated Greek germplasm and a representative of a local wild cherry elite phenotype. The 21 genotypes were sequenced in an average depth of coverage of 33.91×. and effective mapping depth, to the genomic reference sequence of ‘Satonishiki’ cultivar, between 22.21× to 36.62×. Discriminant analysis of principal components (DAPC) with SNPs revealed two clusters of genotypes. There was a rapid linkage disequilibrium decay, as the majority of SNP pairs with r 2 in near complete disequilibrium (>0.8) were found at physical distances less than 10 kb. Functional analysis of the variants showed that the genomic ratio of non-synonymous/synonymous (dN/dS) changes was 1.78. The higher dN frequency in the Greek cohort of sweet cherry could be the result of artificial selection pressure imposed by breeding, in combination with the vegetative propagation of domesticated cultivars through grafting. The majority of SNPs with high impact (e.g., stop codon gaining, frameshift), were identified in genes involved in flowering time, dormancy and defense reactions against pathogens, providing promising resources for future breeding programs. Our study has established the foundation for further large scale characterization of sweet cherry germplasm, enabling breeders to incorporate diverse germplasm and allelic variants to fine tune flowering and maturity time and disease resistance in sweet cherry cultivars.

The different levels of biodiversity (genetic diversity, species diversity, ecosystem diversity) present in Greece are introduced, quantified, where possible, and analysed in comparison to the rest of the European continent and internationally. Greece ranks third and fourth regarding key biodiversity areas in Europe and Mediterranean Basin respectively and first in the number of species per unit area. The genetic diversity and differentiation in natural ecosystems and especially in forest tree species is very high. For a number of species (e.g. in chestnut) a significant portion of their total European genetic diversity is present in Greece and some metrics of genetic diversity parameters present high values when compared to European and world-wide average values. Nevertheless, the conservation of biodiversity has insofar focused at the ecosystem level. About one-third of the country land mass is under some form of biodiversity protection (27% included in the Natura 2000 network), however the forest genetic resources protection lags behind as officially only 5 species and 15 populations are part of the European Forest Genetic Resources Network. Overall, the richness for biodiversity in Greece is almost irreversibly proportional to the stage of its protection, especially at the genetic resource level.

Forest tree genetic monitoring and conservation are of the utmost significance for the persistence of natural forests. Genetic conservation aspires to guard and maintain genetic diversity which is crucial for safeguarding species adaptive potential. Genetic monitoring is the quantification of time-based alterations in population genetic structure and diversity which expose processes that preserve genetic variation in nature, pioneering prognosis and assisting in defining instruments for forest genetic resource management. Genetic monitoring is founded on the geneecological approach and therefore the proposed indicators are linked to the evaluation of genetic variation, genetic drift, gene flow, mating systems and natural selection. The development of genetic baseline data for the application of genetic monitoring in forest conservation areas in Greece is presented as a case study.

An increasing demand for cherry production ( Prunus avium L.) in Greece led to the development of new high quality sweet cherry cultivars. Self-incompatibility in cherry is one of the most challenging issues for the species’ cultivation and top breeding priority. Τhe present study focuses on the development of new hybrids with improved traits such as productivity, fruit size, organoleptic characteristics and self-compatibility. For this purpose, thirty different cultivars were crossed and produced hybrids that were evaluated according to 34 morpho-physiological characteristics. The results were analyzed using the XLSTAT (version 2014.1) software and a dendrogram was constructed using the agglomerative hierarchical clustering method. Optimal hybrid clustering was achieved when characteristics of great economic importance such as fruit shape and size, growth habit and days to blooming were included in the analysis. Based on the results, new sweet cherry hybrids with the special character of self-compatibility were developed. Our findings provide crucial new information for sweet cherry future breeding programs and cultivation.