Mateusz Liziniewicz

Since ash dieback was reported in Sweden in 2001, the invasive fungus Hymenoscyphus fraxineus has caused mortality of Fraxinus excelsior , threatening biodiversity, ecosystem functions, landscapes, and hundreds of associated species. This perspective reviews more than a decade of conservation efforts led by Rädda Asken (“Save the Ash”), a citizen science initiative launched in 2013 without dedicated state funding. Public engagement identified nearly 1300 putatively resistant trees, enabled clonal propagation, and established conservation and breeding infrastructure. Research showing that resistance is heritable supports breeding and restoration. However, fragmented financing and limited national coordination have restricted progress. Key uncertainties concern the durability of resistance, maintenance of genetic diversity, secondary pathogens, and the threat of Agrilus planipennis . Sweden’s experience demonstrates both the value and limitations of grassroots conservation efforts. Future recovery of ash and its associated biodiversity will require sustained investment in breeding and research, in addition to a coordinated, long-term restoration programme that supports implementation, monitoring and adaptive management.

Hymenoscyphus fraxineus is an invasive pathogen native to East Asia, responsible for the widespread mortality of European ash ( Fraxinus excelsior ) throughout Europe. Asian ash species, which co-evolved with H. fraxineus , are considered more tolerant than European ash. However, within European ash populations, a small proportion of genotypes show low susceptibility to the pathogen. This study sought to characterize the underlying defence mechanisms to H. fraxineus by performing untargeted constitutive metabolomics profiling of phloem and leaf tissue of from thirteen F. excelsior genotypes (nine tolerant and four susceptible) and five genotypes representing three Asian ash species ( F. mandshurica , F. platypoda , and F. chinensis ). Here we report 57 and 36 compounds associated with lower or higher disease susceptibility, from phloem and leaf tissue, respectively. Flavonoids and coumarins were the main classes of detected compounds. In particular, quercitrin and fraxetin exhibited greater variation among the groups. In phloem tissue, quercitrin and fraxetin were more abundant in tolerant than in susceptible European ash and, lowest in Asian ash species. In leaves, however, quercitrin was highest in Asian ash, followed by tolerant and then susceptible European ash. Other flavonoids, coumarins, and iridoid glycosides also showed variation among groups, with stronger differences in phloem than in leaf tissue. Overall, this study advances our understanding of metabolite composition in Fraxinus species with different co-evolutionary histories and susceptibility to H. fraxineus and demonstrates the potential of untargeted metabolomics for investigating defence-related mechanisms in plant-pathogen interactions.

Key message: Enhancing the efficiency and precision of breeding programs necessitates the implementation of “high-throughput” phenotyping. By employing various sensors for rapid and frequent measurements, we can gather extensive datasets crucial for conventional breeding efforts. This approach not only holds promise for improving forest production but also for evaluating emerging challenges such as fungal infestations and drought damage. Our research demonstrates the efficiency of utilizing height data derived from LiDAR analysis to identify superior genotypes within the Scots pine breeding program, aimed at enhancing volume production. Context: Cost-effective ‘high-throughput’ phenotyping methods would be highly valuable in both conventional and advanced molecular tree breeding programs. Light Detection and Ranging (LiDAR) systems installed on unmanned aerial vehicles (UAVs, drones) have highly promising potential for such purposes as they enable rapid acquisition of relevant data. Aims: To assess their current capacity, we have compared heights from conventional and LiDAR-based measurements in a Scots pine clonal/progeny trial (9 years old) in central Sweden. We have also compared effects of using them to obtain relationships between phenotypic and genetic parameters, and for selection. Methods: The study was done in a Scots pine genetic field trial that included clones and seedlings. Mean values and estimation of genetic parameters for height were compared between datasets obtained by conventional measurements and by analysis of LiDAR objects obtained by a drone. The potential influence of the measurement method on genetic selection was quantified. Results: The phenotypic correlations between heights obtained with the two methods were very high (≥ 0.9) and so were both the genetic correlations and estimated heritabilities. Selections of the best clones within tested families using the two sets of measurements matched almost perfectly. A wrong clone with a difference in rank of more than one was selected for just one family (of 47). The findings highlight the great potential of the approach for use in breeding practices, as it will allow the collection of vast amounts of accurate data much cheaper than conventional measurements.

Common ash (Fraxinus excelsior) is under intensive attack from the invasive alien pathogenic fungus Hymenoscyphus fraxineus, causing ash dieback at epidemic levels throughout Europe. Previous studies have found significant genetic variation among genotypes in ash dieback susceptibility and that host phenology, such as autumn yellowing, is correlated with susceptibility of ash trees to H. fraxineus; however, the genomic basis of ash dieback tolerance in F. excelsior requires further investigation. Here, we integrate quantitative genetics based on multiple replicates and genome‐wide association analyses with machine learning to reveal the genetic architecture of ash dieback tolerance and of phenological traits in F. excelsior populations in six European countries (Austria, Denmark, Germany, Ireland, Lithuania, Sweden). Based on phenotypic data of 486 F. excelsior replicated genotypes we observed negative genotypic correlations between crown damage caused by ash dieback and intensity of autumn leaf yellowing within multiple sampling sites. Our results suggest that the examined traits are polygenic and using genomic prediction models, with ranked single nucleotide polymorphisms (SNPs) based on GWAS associations as input, a large proportion of the variation was predicted by unlinked SNPs. Based on 100 unlinked SNPs, we can predict 55% of the variation in disease tolerance among genotypes (as phenotyped in genetic trials), increasing to a maximum of 63% when predicted from 9155 SNPs. In autumn leaf yellowing, 52% of variation is predicted by 100 unlinked SNPs, reaching a peak of 72% using 3740 SNPs. Based on feature permutations within genomic prediction models, a total of eight nonsynonymous SNPs linked to ash dieback crown damage and autumn leaf yellowing (three and five SNPs, respectively) were identified, these were located within genes related to plant defence (pattern triggered immunity, pathogen detection) and phenology (regulation of flowering and seed maturation, auxin transport). We did not find an overlap between genes associated with crown damage level and autumn leaf yellowing. Hence, our results shed light on the difference in the genomic basis of ADB tolerance and autumn leaf yellowing despite these two traits being correlated in quantitative genetic analysis. Overall, our methods show the applicability of genomic prediction models when combined with GWAS to reveal the genomic architecture of polygenic disease tolerance enabling the identification of ash dieback tolerant trees for breeding or conservation purposes.

Traditional oak silviculture is costly due to high initial planting density required to obtain management goals of producing high quality timber. New methods therefore reduce the initial planting density and use a planting pattern that allows the inclusion of naturally regenerated trees of other species. The study presents the results of a 13-year experiment on the growth and quality of sessile oak planted in traditional and three alternative planting patterns. We hypothesized that increasing of initial spacing and use of natural regeneration to compensate for lower intra-specific competition does not deteriorate growth and quality parameters of oak. Breast height diameter, height, slenderness, height of the first live branch, diameter of the thickest branch, stem shape and potential future crop oak trees (PFCT) were measured and analysed. The local competition of admixture species was estimated on the basis of the relationship between the height of the oak and the height of admixture trees in its close proximity. The type of planting pattern had no significant effect on oak diameter, but oak height was greater in the traditional pattern than in alternative patterns. Height of the first live branch was the only qualitative trait that differed significantly between the compared planting patterns. The probability of an oak being selected as a PFCT was similar in traditional and alternative patterns, but PFCT absolute number was increasing with an increase of oak planting density. Analysis of competition of admixture species in alternative methods shows that it can reduce height, diameter and stability of oaks. On the other hand, the probability of trees being selected as a PFCT increases significantly with increasing interspecific competition. We conclude that, with controlled competition and at least moderate natural regeneration, the alternative planting patterns can produce oaks with similar growth and quality to those in the traditional pattern.

This study investigated whether improved downy birch could perform as well as improved silver birch, and whether there was sufficient genetic variation and control for non-destructive testing (NDT) values to include them as selection traits in breeding programs. NDT tools were applied to a 15-year-old downy birch family trial intermixed with improved silver birch. Average diameters, fissured bark height, and grain angle were higher for silver than downy birch. The genetic analysis for downy birch provided estimates of narrow-sense heritability (h²) for acoustic velocity and Pilodyn penetration depth that were above 0.3 but had low genetic variation. Grain angle had relatively high genetic variability (18%) and an h² of 0.20. A subsample of 49 trees had 4 mm cores x-rayed for wood density estimates, and 34 stems had 12 mm cores macerated for cell measurements. t-tests revealed that average wood density and cell measurements were not significantly different between species. For silver and downy birch, fiber length and vessel length increased between inner and outer measurement positions, and fiber length was reasonably correlated with acoustic velocity. Silver birch tended to have denser and stiffer wood, while downy birch had less rough bark and straighter grain, and these results are in agreement with existing knowledge. The h² values were similar to those observed in other birch species and indicate there is potential to breed for improved wood density and grain angle in downy birch.

Summary: Plants rely on cross‐resistance traits to defend against multiple, phylogenetically distinct enemies. These traits are often the result of long co‐evolutionary histories. Biological invasions can force naïve plants to cope with novel, coincident pests, and pathogens. For example, European ash (Fraxinus excelsior) is substantially threatened by the emerald ash borer (EAB), Agrilus planipennis, a wood‐boring beetle, and the ash dieback (ADB) pathogen, Hymenoscyphus fraxineus. Yet, plant cross‐resistance traits against novel enemies are poorly explored and it is unknown whether naïve ash trees can defend against novel enemy complexes via cross‐resistance mechanisms. To gain mechanistic insights, we quantified EAB performance on grafted replicates of ash genotypes varying in ADB resistance and characterized ash phloem chemistry with targeted and untargeted metabolomics. Emerald ash borer performed better on ADB‐susceptible than on ADB‐resistant genotypes. Moreover, changes in EAB performance aligned with differences in phloem chemical profiles between ADB‐susceptible and ADB‐resistant genotypes. We show that intraspecific variation in phloem chemistry in European ash can confer increased cross‐resistance to invasive antagonists from different taxonomic kingdoms. Our study suggests that promotion of ADB‐resistant ash genotypes may simultaneously help to control the ADB disease and reduce EAB‐caused ash losses, which may be critical for the long‐term stability of this keystone tree species.

Investing in planting genetically improved silver birch ( Roth) in Swedish plantations requires understanding how birch stands will develop over their entire rotation. Previous studies have indicated relatively low production of birch compared to Norway spruce ( (L.) Karst.) and Scots pine ( L.). This could result from using unrepresentative basic data, collected from unimproved, naturally-regenerated birch ( spp.) growing on inventory plots often located in coniferous stands. The objective of this study was to develop a basal area development function of improved silver birch and evaluate production over a full rotation period. We used data from 52 experiments including planted silver birch of different genetic breeding levels in southern and central Sweden. The experimental plots were established on fertile forest sites and on former agricultural lands, and were managed with different numbers of thinnings and basal area removal regimes. The model best describing total stand basal area development was a dynamic equation derived from the Korf base model. The analysis of the realized gain trial for birch showed a good stability of the early calculated relative differences in basal area between tested genotypes over time. Thus, the relative difference in basal area might be with cautious used as representation of the realized genetic gain. On average forest sites in southern Sweden, improved and planted silver birch could produce between 6–10.5 m ha year, while on fertile agriculture land the average productivity might be higher, especially with material coming from the improvement program. The performed analysis provided a first step toward predicting the effects of genetic improvement on total volume production and profitability of silver birch. However, more experiments are needed to set up the relative differences between different improved material.Betula pendula Picea abies Pinus sylvestris Betula 3 –1 –1

This study investigated heritability of stem and wood traits to improve Swedish silver birch (Betula pendula Roth.) through breeding. Birch is 12% of Sweden’s forest area but mainly used for low value pulp or firewood. This paper applied non-destructive test (NDT) methods, and estimated traits’ heritability (h²), to help breed birch for high value solid wood products. Two trials of 22 families were assessed at age 19 for stem diameter (DBH), stem straightness, rough brown bark height (BH), grain angle (GA), Pilodyn penetration depth (Pilo) and acoustic velocity (AV). X-ray densitometry was performed on a subsample of radial cores taken at 1.3 m from the ground to get an average benchmark density. The h² values were moderate for GA (0.20 and 0.21) and Pilo (0.53 and 0.48) at the two sites, but the h² values for AV were low (0.05 and 0.30). There were moderate genotypic correlations between BH and DBH (0.51–0.54). There were low genotypic and phenotypic correlations between NDT measurements and other traits so including NDT in birch breeding efforts should not inadvertently reduce size, stem or wood quality. The high genetic correlations between sites suggest that GA, Pilo and AV values were determined more by genotype than by environment.