Biografi

Jeg forsker på samspillet mellom insekter og planter og særlig hvordan bartrær forsvarer seg mot barkbiller og blåvedsopp. Jeg samarbeider ofte med kjemikere, molekylærbiologer og økologer ved NIBIO og andre institusjoner i inn- og utland. Metodene vi bruker spenner fra feltforsøk til kjemisk økologi og molekylærbiologi. Jeg har jobbet i NIBIO (tidligere Skogforsk, Skog og landskap) siden 1992. Min utdanning har jeg fra Universitetet i Oslo, der jeg ble Cand. scient. i økologi/entomologi i 1992 og Dr. Scient. i skogentomologi i 1996. Jeg har en bistilling (20 %) som professor II ved Norges miljø- og biovitenskapelige universitet (NMBU), der jeg underviser i skogentomologi. Fra 2018 er jeg også medlem av Vitenskapskomiteen for mat og miljø, faggruppe plantehelse.

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Convergent evolution of semiochemical use in organisms from different Kingdoms is a rarely described phenomenon. Tree-killing bark beetles vector numerous symbiotic blue-stain fungi that help the beetles colonize healthy trees. Here we show for the first time that some of these fungi are able to biosynthesize bicyclic ketals that are pheromones and other semiochemicals of bark beetles. Volatile emissions of five common bark beetle symbionts were investigated by gas chromatography-mass spectrometry. When grown on fresh Norway spruce bark the fungi emitted three well-known bark beetle aggregation pheromones and semiochemicals (exo-brevicomin, endo-brevicomin and trans-conophthorin) and two structurally related semiochemical candidates (exo-1,3-dimethyl-2,9-dioxabicyclo[3.3.1]nonane and endo-1,3-dimethyl-2,9-dioxabicyclo[3.3.1]nonane) that elicited electroantennogram responses in the spruce bark beetle Ips typographus. When grown on malt agar with 13C D-Glucose, the fungus Grosmannia europhioides incorporated 13C into exo-brevicomin and trans-conophthorin. The enantiomeric compositions of the fungus-produced ketals closely matched those previously reported from bark beetles. The production of structurally complex bark beetle pheromones by symbiotic fungi indicates cross-kingdom convergent evolution of signal use in this system. This signaling is susceptible to disruption, providing potential new targets for pest control in conifer forests and plantations.

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1 The European spruce bark beetle Ips typographus is a damaging pest on spruce in Europe. Beetle interactions with tree species originating outside the natural range of the beetle are largely unknown and may be unpredictable because trees without a co-evolutionary history with the beetle may lack effective defences. 2 The terpenoid composition and breeding suitability for I. typographus of the historic host Norway spruce Picea abies were compared with two evolutionary naïve spruces of North American origin that are extensively planted in North-West Europe: Sitka spruce Picea sitchensis and Lutz spruce Picea glauca x lutzii. 3 The bark of all three species had a similar chemical composition and similar levels of total constitutive terpenoids, although Norway spruce had higher total induced terpenoid levels. 4 Beetles tunnelling in the three spruce species produced similar amounts of aggregation pheromone. Controlled breeding experiments showed that I. typographus could produce offspring in all three species, with a similar offspring length and weight across species. However, total offspring production was much lower in Sitka and Lutz spruce. 5 Overall, the results of the present study suggest that I. typographus will be able to colonize Sitka and Lutz spruce in European plantations and in native spruce forests in North America if introduced there.

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The purpose of this study is to increase the basic understanding of outbreak dynamics in order to improve the management of bark beetle outbreaks. The spruce bark beetle Ips typographus is a major disturbance agent of European forests and is the continent’s most economically and environmentally damaging bark beetle. Outbreaks of the spruce bark beetle are often triggered by large windfall episodes, and we have utilized a unique opportunity to study a Slovakian outbreak where little salvage logging was performed in some areas after a 2.5 million m3 storm-felling in 2004. Our analyses focused on the first five years after the windfall, and we used a combination of empirical data and simulation models to understand the spatial patterns of beetle-killed forest patches developing during the outbreak. The univoltine beetle population used an increasing proportion of the windfelled trees during the two first seasons after the storm, but from the third season onwards our comparisons of inter-patch distance distributions indicated a transition from beetle production largely in windfall areas to a self-sustaining outbreak with infestation patches developing independently of the windthrows. The size of new infestation patches formed after this transition was modeled as a function of beetle pressure, estimated by the proportion of a circle area surrounding new patches that was covered by infestation patches the previous year. Our model results of patch size distribution did not correspond well with the empirical data if patch formation was modeled as a pure dispersal–diffusion process. However, beetle aggregation on individual trees appears to be important for patch development, since good correspondence with empirical data was found when beetle aggregation was incorporated in the modeled dispersal process. The strength of correspondence between the beetle aggregation model and the empirical data varied with the density of aggregation trees in the modeled landscape, and reached a maximum of 83% for a density of three aggregation trees per infestation patch. Our results suggest that efficient removal of windfelled trees up until the start of the second summer after a major windfall is important to avoid a transition into a patch-driven bark beetle outbreak that is very difficult to manage. Our results also indicate that the outcome of a patch-driven outbreak is difficult to predict, since the development of new infestation patches is not a simple function of beetle pressure but is also affected by beetle behavior and local forest conditions.

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Climate change is already reducing carbon sequestration in Central European forests dramatically through extensive droughts and bark beetle outbreaks. Further warming may threaten the enormous carbon reservoirs in the boreal forests in northern Europe unless disturbance risks can be reduced by adaptive forest management. The European spruce bark beetle (Ips typographus) is a major natural disturbance agent in spruce-dominated forests and can overwhelm the defences of healthy trees through pheromone-coordinated mass-attacks. We used an extensive dataset of bark beetle trap counts to quantify how climatic and management-related factors influence bark beetle population sizes in boreal forests. Trap data were collected during a period without outbreaks and can thus identify mechanisms that drive populations towards outbreak thresholds. The most significant predictors of bark beetle population size were the volume of mature spruce, the extent of newly exposed clearcut edges, temperature and soil moisture. For clearcut edge, temperature and soil moisture, a 3-year time lag produced the best model fit. We demonstrate how a model incorporating the most significant predictors, with a time lag, can be a useful management tool by allowing spatial prediction of future beetle population sizes. Synthesis and Applications: Some of the population drivers identified here, i,e., spruce volume and clearcut edges, can be targeted by adaptive management measures to reduce the risk of future bark beetle outbreaks. Implementing such measures may help preserve future carbon sequestration of European boreal forests.

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Highlights • Methyl jasmonate has been used for more than 20 years to study conifer inducible defenses. • We summarized the key experimental methods used to study methyl jasmonate effects on conifers. • Meta-analysis showed that methyl jasmonate significantly reduces growth and pest/pathogen damage. • We identified important knowledge gaps that hinder the practical use of methyl jasmonate as a protective measure in forestry.

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Bark beetle (Ips typographus) outbreaks have the potential to damage large areas of spruce-dominated forests in Scandinavia. To define forest management strategies that will minimize the risk of bark beetle attacks, we need robust models that link forest structure and composition to the risk and potential damage of bark beetle attacks. Since data on bark beetle infestation rates and corresponding damages does not exist in Norway, we implement a previously published meta-model for estimating I. typographus damage probability and intensity. Using both current and projected climatic conditions we used the model to estimate damage inflicted by I. typographus in Norwegian spruce stands. The model produces feasible results for most of Norway’s climate and forest conditions, but a revised model tailored to Norway should be fitted to a dataset that includes older stands and lower temperatures. Based on current climate and forest conditions, the model predicts that approximately nine percent of productive forests within Norway’s main spruce-growing region will experience a loss ranging from 1.7 to 11 m3/ha of spruce over a span of five years. However, climate change is predicted to exacerbate the annual damage caused by I. typographus, potentially leading to a doubling of its detrimental effects.

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Purpose of Review Forestry in northern temperate and boreal regions relies heavily on conifers. Rapid climate change and associated increases in adverse growing conditions predispose conifers to pathogens and pests. The much longer generation time and presumably, therefore, lower adaptive capacity of conifers relative to their native or non-native biotic stressors may have devastating consequences. We provide an updated overview of conifer defences underlying pathogen and pest resistance and discuss how defence traits can be used in tree breeding and forest management to improve resistance. Recent Findings Breeding of more resilient and stress-resistant trees will benefit from new genomic tools, such as genotyping arrays with increased genomic coverage, which will aid in genomic and relationship-based selection strategies. However, to successfully increase the resilience of conifer forests, improved genetic materials from breeding programs must be combined with more flexible and site-specific adaptive forest management. Summary Successful breeding programs to improve conifer resistance to pathogens and pests provide hope as well as valuable lessons: with a coordinated and sustained effort, increased resistance can be achieved. However, mechanisms underlying resistance against one stressor, even if involving many genes, may not provide any protection against other sympatric stressors. To maintain the adaptive capacity of conifer forests, it is important to keep high genetic diversity in the tree breeding programs. Choosing forest management options that include diversification of tree-species and forest structure and are coupled with the use of genetically improved plants and assisted migration is a proactive measure to increase forest resistance and resilience to foreseen and unanticipated biotic stressors in a changing climate.

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Drought-induced mortality is a major direct effect of climate change on tree health, but drought can also affect trees indirectly by altering their susceptibility to pathogens. Here, we report how a combination of mild or severe drought and pathogen infection affected the growth, pathogen resistance and gene expression in potted 5-year-old Norway spruce trees [Picea abies (L.) Karst.]. After 5 weeks of drought, trees were inoculated with the fungal pathogen Endoconidiophora polonica. Combined drought–pathogen stress over the next 8 weeks led to significant reductions in the growth of drought-treated trees relative to well-watered trees and more so in trees subjected to severe drought. Belowground, growth of the smallest fine roots was most affected. Aboveground, shoot diameter change was most sensitive to the combined stress, followed by shoot length growth and twig biomass. Both drought-related and some resistance-related genes were upregulated in bark samples collected after 5 weeks of drought (but before pathogen infection), and gene expression levels scaled with the intensity of drought stress. Trees subjected to severe drought were much more susceptible to pathogen infection than well-watered trees or trees subjected to mild drought. Overall, our results show that mild drought stress may increase the tree resistance to pathogen infection by upregulating resistance-related genes. Severe drought stress, on the other hand, decreased tree resistance. Because drought episodes are expected to become more frequent with climate change, combined effects of drought and pathogen stress should be studied in more detail to understand how these stressors interactively influence tree susceptibility to pests and pathogens.

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An epigenetic memory of the temperature sum experienced during embryogenesis is part of the climatic adaptation strategy of the long-lived gymnosperm Norway spruce. This memory has a lasting effect on the timing of bud phenology and frost tolerance in the resulting epitype trees. The epigenetic memory is well characterized phenotypically and at the transcriptome level, but to what extent DNA methylation changes are involved have not previously been determined. To address this, we analyzed somatic epitype embryos of Norway spruce clones produced at contrasting epitype-inducing conditions (18 and 28°C). We screened for differential DNA methylation in 2744 genes related mainly to the epigenetic machinery, circadian clock, and phenology. Of these genes, 68% displayed differential DNA methylation patterns between contrasting epitype embryos in at least one methylation context (CpG, CHG, CHH). Several genes related to the epigenetic machinery (e.g., DNA methyltransferases, ARGONAUTE) and the control of bud phenology (FTL genes) were differentially methylated. This indicates that the epitype-inducing temperature conditions induce an epigenetic memory involving specific DNA methylation changes in Norway spruce.

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I 2023 går fangstene av stor granbarkbille opp i alle fylker med unntak av Vestfold og Nordland. Årets fangster er spesielt høye i Akershus og Oslo, Buskerud og Oppland. I Buskerud, Hedmark og Telemark er fangstene de høyeste på 10-20 år, og i Oppland er fangstene de høyeste noensinne. For Sør-Norge sett under ett må man tilbake til 1994 for å finne høyere fangster. I noen fylker kan årets økning være en forsinket respons på stormfellingene i november 2021, siden stormrammede områder i Oppland og Buskerud har spesielt høye verdier. Det rapporteres om en del angrep på stående skog i områder som ble rammet av vesentlige vindfellinger under stormen i 2021. Årets barkbillesesong var preget av en svært tørr og varm juni, mens juli og august var svært til ekstremt våt og til dels kjølig. Det varme været i juni var gunstig for flukt, egglegging og larveutvikling hos granbarkbillen. Tørken kan også ha stresset granskogen og gjort den mindre motstandsdyktig mot barkbilleangrep. Det våte og kjølige været resten av sommeren har trolig vært positivt for trærne og noe negativt for billene. Men for 2023-sesongen sett under ett har trolig ikke en våt og kjølig avslutning fullt ut veid opp for tørken i juni. En eventuell økning i billebestandene som følge av juni-tørken i år forventes først å komme om noen år. Beregninger fra en temperaturbasert utviklingsmodell indikerer at granbarkbillene per 1. oktober kan ha rukket å gjennomføre to generasjoner i området rundt Oslofjorden og langs sørlandskysten.

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Denne rapporten gjør rede for metoder brukt for å fremstille temakart for framskrivninger av klima i Tønsberg og Drammen for perioden 2040-2070. Kartene skal gjøres tilgjengelige i kommunenes kartportaler. Temakartene går inn i en større leveranse av temakart over arealdekkets rolle i arbeidet med klimatilpasning, samt klimagassutslipp fra arealbruk og arealbruksendringer for Tønsberg og Drammen kommune. Oppdragene er finansiert med Klimasats-ordningen til Miljødirektoratet.

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Stress can have long-lasting impacts on plants. Here we report the long-term effects of the stress hormone jasmonic acid (JA) on the defence phenotype, transcriptome and DNA methylome of Arabidopsis. Three weeks after transient JA signalling, 5-week-old plants retained induced resistance (IR) against herbivory but showed increased susceptibility to pathogens. Transcriptome analysis revealed long-term priming and/or upregulation of JA-dependent defence genes but repression of ethylene- and salicylic acid-dependent genes. Long-term JA-IR was associated with shifts in glucosinolate composition and required MYC2/3/4 transcription factors, RNA-directed DNA methylation, the DNA demethylase ROS1 and the small RNA (sRNA)-binding protein AGO1. Although methylome analysis did not reveal consistent changes in DNA methylation near MYC2/3/4-controlled genes, JA-treated plants were specifically enriched with hypomethylated ATREP2 transposable elements (TEs). Epigenomic characterization of mutants and transgenic lines revealed that ATREP2 TEs are regulated by RdDM and ROS1 and produce 21 nt sRNAs that bind to nuclear AGO1. Since ATREP2 TEs are enriched with sequences from IR-related defence genes, our results suggest that AGO1-associated sRNAs from hypomethylated ATREP2 TEs trans-regulate long-lasting memory of JA-dependent immunity.

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A major challenge for plants in a rapidly changing climate is to adapt to rising temperatures. Some plants adapt to temperature conditions by generating an epigenetic memory that can be transmitted both meiotically and mitotically. Such epigenetic memories may increase phenotypic variation to global warming and provide time for adaptation to occur through classical genetic selection. The goal of this study was to understand how warmer temperature conditions experienced during sexual and asexual reproduction affect the transcriptomes of different strawberry (Fragaria vesca) ecotypes. We let four European F. vesca ecotypes reproduce at two contrasting temperatures (18 and 28°C), either asexually through stolon formation for several generations, or sexually by seeds (achenes). We then analyzed the transcriptome of unfolding leaves, with emphasis on differential expression of genes belonging to the epigenetic machinery. For asexually reproduced plants we found a general transcriptomic response to temperature conditions but for sexually reproduced plants we found less significant responses. We predicted several splicing isoforms for important genes (e.g. a SOC1, LHY, and SVP homolog), and found significantly more differentially presented splicing event variants following asexual vs. sexual reproduction. This difference could be due to the stochastic character of recombination during meiosis or to differential creation or erasure of epigenetic marks during embryogenesis and seed development. Strikingly, very few differentially expressed genes were shared between ecotypes, perhaps because ecotypes differ greatly both genetically and epigenetically. Genes related to the epigenetic machinery were predominantly upregulated at 28°C during asexual reproduction but downregulated after sexual reproduction, indicating that temperature-induced change affects the epigenetic machinery differently during the two types of reproduction.

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The large pine weevil (Hylobius abietis) is a major regeneration pest in commercial forestry. Pesticide application has historically been the preferred control method, but pesticides are now being phased out in several countries for environmental reasons. There is, thus, a need for alternative plant protection strategies. We applied methyl jasmonate (MeJA), salicylic acid (SA) or oxalic acid (OxA) on the stem of 2-year-old Norway spruce (Picea abies) plants to determine effects on inducible defenses and plant growth. Anatomical examination of stem cross-sections 9 weeks after application of 100 mM MeJA revealed massive formation of traumatic resin ducts and greatly reduced sapwood growth. Application of high concentrations of SA or OxA (500 and 200 mM, respectively) induced much weaker physiological responses than 100 mM MeJA. All three treatments reduced plant height growth significantly, but the reduction was larger for MeJA (~55%) than for SA and OxA (34-35%). Lower MeJA concentrations (5-50 mM) induced comparable traumatic resin duct formation as the high MeJA concentration but caused moderate (and non-significant) reductions in plant growth. Two-year-old spruce plants treated with 100 mM MeJA showed reduced mortality after exposure to pine weevils in the field, and this enhanced resistance-effect was statistically significant for three years after treatment.

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Temperature conditions experienced during embryogenesis and seed development may induce epigenetic changes that increase phenotypic variation in plants. Here we investigate if embryogenesis and seed development at two different temperatures (28 vs. 18°C) result in lasting phenotypic effects and DNA methylation changes in woodland strawberry (Fragaria vesca). Using five European ecotypes from Spain (ES12), Iceland (ICE2), Italy (IT4), and Norway (NOR2 and NOR29), we found statistically significant differences between plants from seeds produced at 18 or 28°C in three of four phenotypic features investigated under common garden conditions. This indicates the establishment of a temperature-induced epigenetic memory-like response during embryogenesis and seed development. The memory effect was significant in two ecotypes: in NOR2 flowering time, number of growth points and petiole length were affected, and in ES12 number of growth points was affected. This indicates that genetic differences between ecotypes in their epigenetic machinery, or other allelic differences, impact this type of plasticity. We observed statistically significant differences between ecotypes in DNA methylation marks in repetitive elements, pseudogenes, and genic elements. Leaf transcriptomes were also affected by embryonic temperature in an ecotype-specific manner. Although we observed significant and lasting phenotypic change in at least some ecotypes, there was considerable variation in DNA methylation between individual plants within each temperature treatment. This within-treatment variability in DNA methylation marks in F. vesca progeny may partly be a result of allelic redistribution from recombination during meiosis and subsequent epigenetic reprogramming during embryogenesis.

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Skogens helsetilstand påvirkes i stor grad av klima og værforhold, enten direkte ved tørke, frost og vind, eller indirekte ved at klimaet påvirker omfanget av soppsykdommer og insektangrep. Klimaendringene og den forventede økningen i klimarelaterte skogskader gir store utfordringer for forvaltningen av framtidas skogressurser. Det samme gjør invaderende skadegjørere, både allerede etablerte arter og nye som kan komme til Norge i nær framtid. I denne rapporten presenteres resultater fra skogskadeovervåkingen i Norge i 2021 og trender over tid for følgende temaer: (i) Landsrepresentativ skogovervåking; (ii) Skogøkologiske analyser og målinger av luftkjemi på de intensive overvåkingsflatene; (iii) Overvåking av bjørkemålere i Troms og Finnmark; (iv) Barkbilleovervåkingen 2021 og mulig overgang til to generasjoner; (v) Asiatisk askepraktbille – en dørstokkart? (vi) Overvåking av askeskuddsyke; (vii) Andre spesielle skogskader i 2021.

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Skogens helsetilstand påvirkes i stor grad av klima og værforhold, enten direkte ved tørke, frost og vind, eller indirekte ved at klimaet påvirker omfanget av soppsykdommer og insektangrep. Klimaendringene og den forventede økningen i klimarelaterte skogskader gir store utfordringer for forvaltningen av framtidas skogressurser. Det samme gjør invaderende skadegjørere, både allerede etablerte arter og nye som kan komme til Norge i nær framtid. I denne rapporten presenteres resultater fra skogskadeovervåkingen i Norge i 2022 og trender over tid for følgende temaer: (i) Landsrepresentativ skogovervåking; (ii) Intensiv skogovervåking; (iii) Overvåking av bjørkemålere i Troms og Finnmark; (iv) Barkbilleovervåkingen; (v) Furuvednematode; (vi) Askeskuddsyke; (vii) Andre spesielle skogskader i 2022.

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The European spruce bark beetle Ips typographus and the North American spruce beetle Dendroctonus rufipennis cause high mortality of spruces on their native continents. Both species have been inadvertently transported beyond their native ranges. With similar climates and the presence of congeneric spruce hosts in Europe and North America, there is a risk that one or both bark beetle species become established into the non-native continent. There are many challenges that an introduced population of bark beetles would face, but an important prerequisite for establishment is the presence of suitable host trees. We tested the suitability of non-native versus native hosts by exposing cut bolts of Norway spruce (Picea abies), black spruce (Picea mariana) and white spruce (Picea glauca) to beetle attacks in the field in Norway and Canada. We quantified attack density, brood density and reproductive success of I. typographus and D. rufipennis in the three host species. We found that I. typographus attacked white and black spruce at comparable densities to its native host, Norway spruce, and with similar reproductive success in all three host species. In contrast, D. rufipennis strongly preferred to attack white spruce (a native host) but performed better in the novel Norway spruce host than it did in black spruce, a suboptimal native host. Our results suggest that I. typographus will find abundant and highly suitable hosts in North America, while D. rufipennis in Europe may experience reduced reproductive success in Norway spruce.

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Key words: VKM, pest risk analysis, Norwegian Scientific Committee for Food and Environment, Norwegian Food Safety Authority, Sudden oak death, Phytophthora ramorum Introduction The Norwegian Food Safety Authority has asked the Norwegian Scientific Committee for Food and Environment for an updated pest risk assessment of Phytophthora ramorum in Norway. The previous risk assessment of P. ramorum for Norway is from 2009. Since then, the pathogen has been detected repeatedly in Norway, primarily in parks, garden centres, and nurseries in southwestern Norway. The knowledge base concerning P. ramorum has changed since the last pest risk assessment, with increased genetic knowledge about different populations, lineages, and mating types. The risks associated with P. ramorum have also changed, since the disease has become epidemic in new host plants, such as larch trees in England. This updated pest risk assessment will provide important input to the Norwegian Food Safety Authority’s efforts to develop the Norwegian plant health regulation. Methods VKM established a project group with expertise in plant health, forest pathology, horticultural plant pathology, plant disease modelling, and pest risk assessment. The group conducted systematic literature searches and scrutinized the relevant literature. In the absence of Norwegian studies, VKM relied on literature from other countries. The group did a quantitative risk assessment describing the level of confidence in the conclusions and identifying uncertainties and data gaps. The report underwent pre-submission commenting and external expert reviewing before final approval and publication. Results and conclusions Phytophthora ramorum is present in the PRA area but has a restricted distribution, mainly being detected in the southern and southwestern parts of Norway. The only P. ramorum lineage considered to be present in Norway is EU1 with mating type A1. The other lineage in Europe, EU2, has so far mainly been documented from the UK. The most widely distributed multilocus genotype of P. ramorum in Norway is EU1MLG1, which became dominant in Europe (including Norway) after 2008. In North America, the NA1, NA2, and EU1 lineages are known from both nurseries and forests. NA1 and NA2 are of the opposite mating type (A2) than European lineages. Recently, various other lineages of P. ramorum have been described from Asia. The main risks for future problems with P. ramorum in Norway are related to entry and establishment of non-European isolates (of all lineages), as well as emergence of new genotypes in European P. ramorum populations. There are several options for diagnosing P. ramorum to species and lineage (mainly EU1, EU2, NA1, and NA2). From a management perspective it is more important to distinguish these entities than mating type and isolate groups (genotypes). The latter are mainly relevant for research purposes or in cases of unexpected disease developments, such as new hosts, increased spread or more severe symptoms on known hosts. However, for more detailed regulation, monitoring, and management of P. ramorum it could also be useful to test for genotypes, i.e. to distinguish EU1MLG1 from other genotypes. Rhododendron remains the most important host plant for P. ramorum in Norway, both in terms of imported plants and detections (mainly in nurseries, garden centres, and public parks). Species in other ornamental plant genera, such as Viburnum, Pieris, and Kalmia, are also listed as major hosts in Europe, and P. ramorum has been detected at least once on species in all these genera in Norway. In the US, Rhododendron, Viburnum, Pieris, Syringa, and Camellia are considered to be the main ornamental hosts. .....................

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Plants must adapt with increasing speed to global warming to maintain their fitness. One rapid adaptation mechanism is epigenetic memory, which may provide organisms sufficient time to adapt to climate change. We studied how the perennial Fragaria vesca adapted to warmer temperatures (28°C vs. 18°C) over three asexual generations. Differences in flowering time, stolon number, and petiole length were induced by warmer temperature in one or more ecotypes after three asexual generations and persisted in a common garden environment. Induced methylome changes differed between the four ecotypes from Norway, Iceland, Italy, and Spain, but shared methylome responses were also identified. Most differentially methylated regions (DMRs) occurred in the CHG context, and most CHG and CHH DMRs were hypermethylated at the warmer temperature. In eight CHG DMR peaks, a highly similar methylation pattern could be observed between ecotypes. On average, 13% of the differentially methylated genes between ecotypes also showed a temperature-induced change in gene expression. We observed ecotype-specific methylation and expression patterns for genes related to gibberellin metabolism, flowering time, and epigenetic mechanisms. Furthermore, we observed a negative correlation with gene expression when repetitive elements were found near (±2 kb) or inside genes. In conclusion, lasting phenotypic changes indicative of an epigenetic memory were induced by warmer temperature and were accompanied by changes in DNA methylation patterns. Both shared methylation patterns and transcriptome differences between F. vesca accessions were observed, indicating that DNA methylation may be involved in both general and ecotype-specific phenotypic variation.

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Samtlige fylker i barkbilleovervåkingen viser en nedgang i fangstene i 2022. Dette kan skyldes at effekten av tørken i 2018 avtar, men nye vindfellinger og tørkeperioder i 2022 kan bidra til nye økninger i årene som kommer. Mange rapporter om døde graner på sensommeren kan knyttes til en svært tørr sesong i deler av Sør-Norge, men en eventuell økning i billebestandene forventes å komme senere. De høyeste fangstene i år ble registrert i Vestfold og tilgrensende områder (Kongsberg og Telemark), der det noen steder også ble rapportert om en del barkbilleangrep. Beregninger fra en temperaturdrevet utviklingsmodell indikerer at granbarkbillene kan ha gjennomført to generasjoner denne sesongen i områder rundt Oslofjorden. Dette åpner muligheten for to fluktperioder og mer skade på grunn av granbarkbillene. Lavt nivå av granbarkbiller i Trøndelag og Helgeland kan forklares med at sesongen startet sent og at været har vært fuktig og kjølig i store deler av sommeren i denne landsdelen.

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Tree-killing bark beetles in conifer forests vector symbiotic fungi that are thought to help the beetles kill trees. Fungal symbionts emit diverse volatile blends that include bark beetle semiochemicals involved in mating and host localization. In this study, all 12 tested fungal isolates emitted beetle semiochemicals when growing in medium amended with linoleic acid. These semiochemicals included the spiroacetals chalcogran, trans-conophthorin and exo-brevicomin, as well as 2-methyl-3-buten-1-ol, the main aggregation pheromone component of the spruce bark beetle Ips typographus. The emission of these compounds was affected by the type of fatty acid present (linoleic vs. oleic acid). Accumulating evidence shows that the fatty acid composition in conifer bark can facilitate colonization by bark beetles and symbiotic fungi, whereas the fatty acid composition of non-host trees can be detrimental for beetle larvae or fungi. We hypothesize that beetles probe the fatty acid composition of potential host trees to test their suitability for beetle development and release of semiochemicals by symbiotic fungi.

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Defense priming, the sensitization of inducible defenses, has been extensively studied in annual angiosperms. However, we are just beginning to explore defense priming in woody, long-lived plants. The natural compound methyl jasmonate (MeJA) has been used for over 20 years to study spruce inducible defenses. Recently, it was discovered that MeJA not only directly induces defense, but also primes defense responses in spruce. Metabolite and transcriptional analyses of mature trees treated with MeJA and subsequently wounded showed that while terpenes accumulate at the wound site in a primed manner, terpene biosynthesis genes are directly induced by MeJA. Pathogen resistance (PR) genes, on the other hand, are primed. Sequencing of miRNAs suggests that miRNAs have a regulatory role in MeJA-induced defenses in spruce. Additionally, a detailed transcriptional time course of 2- year-old spruce treated with MeJA indicated that the RNA-directed DNA methylation (RdDM) pathway is involved in the establishment and maintenance of primed defenses. When comparing mechanisms of defense priming in spruce to those in Arabidopsis, it seems that many mechanisms are conserved. However, some aspects, such as jasmonic acid-salicylic acid crosstalk, may be different. Identifying these differences and how they affect forest species is important for practical application of defense priming in forest management.

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Grey mold caused by the necrotrophic fungal pathogen Botrytis cinerea can affect leaves, flowers, and berries of strawberry, causing severe pre- and postharvest damage. The defense elicitor β-aminobutyric acid (BABA) is reported to induce resistance against B. cinerea and many other pathogens in several crop plants. Surprisingly, BABA soil drench of woodland strawberry (Fragaria vesca) plants two days before B. cinerea inoculation caused increased infection in leaf tissues, suggesting that BABA induce systemic susceptibility in F. vesca. To understand the molecular mechanisms involved in B. cinerea susceptibility in leaves of F. vesca plants soil drenched with BABA, we used RNA sequencing to characterize the transcriptional reprogramming 24 h post-inoculation. The number of differentially expressed genes (DEGs) in infected vs. uninfected leaf tissue in BABA-treated plants was 5205 (2237 upregulated and 2968 downregulated). Upregulated genes were involved in pathogen recognition, defense response signaling, and biosynthesis of secondary metabolites (terpenoid and phenylpropanoid pathways), while downregulated genes were involved in photosynthesis and response to auxin. In control plants not treated with BABA, we found a total of 5300 DEGs (2461 upregulated and 2839 downregulated) after infection. Most of these corresponded to those in infected leaves of BABA-treated plants but a small subset of DEGs, including genes involved in ‘response to biologic stimulus‘, ‘photosynthesis‘ and ‘chlorophyll biosynthesis and metabolism’, differed significantly between treatments and could play a role in the induced susceptibility of BABA-treated plants.

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Norway spruce (Picea abies) is an economically and ecologically important tree species that grows across northern and central Europe. Treating Norway spruce with jasmonate has long-lasting beneficial effects on tree resistance to damaging pests, such as the European spruce bark beetle Ips typographus and its fungal associates. The (epi)genetic mechanisms involved in such long-lasting jasmonate induced resistance (IR) have gained much recent interest but remain largely unknown. In this study, we treated 2-year-old spruce seedlings with methyl jasmonate (MeJA) and challenged them with the I. typographus vectored necrotrophic fungus Grosmannia penicillata. MeJA treatment reduced the extent of necrotic lesions in the bark 8 weeks after infection and thus elicited long-term IR against the fungus. The transcriptional response of spruce bark to MeJA treatment was analysed over a 4-week time course using mRNA-seq. This analysis provided evidence that MeJA treatment induced a transient upregulation of jasmonic acid, salicylic acid and ethylene biosynthesis genes and downstream signalling genes. Our data also suggests that defence-related genes are induced while genes related to growth are repressed by methyl jasmonate treatment. These results provide new clues about the potential underpinning mechanisms and costs associated with long-term MeJA-IR in Norway spruce.

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Invasive species are leading causes of biodiversity loss and economic damage. Prevention and management of invasions requires risk assessments based on ecological knowledge for species of potential concern. Interactions between introduced species and heterospecifics in the recipient community may affect the likelihood of establishment through biotic resistance and facilitation and are therefore important predictors of invasion risk. Experimentally exposing one species to another to observe their interactions is not always safe or practical, and containment facilities offer artificial environments which may limit the number of species and the types of interactions that may be tested. To predict biotic resistance and facilitation in a more natural setting, we deployed traps with pheromone lures in the field to mimic the presence of two potentially invasive spruce bark beetles, the European Ips typographus (tested in eastern Canada), and the North American Dendroctonus rufipennis (tested in Norway). We identified and counted possible predators, competitors, and facilitators that were captured in the traps. In eastern Canada, possible predators and competitors responded strongly to I. typographus lures, suggesting the potential for considerable biotic resistance. In Norway, D. rufipennis lures prompted little response by predators or competitors, suggesting that D. rufipennis may experience reduced biotic resistance in Europe. Dendroctonus rufipennis was also attracted to I. typographus pheromone, which may encourage facilitation between these species through cooperative mass attack on trees. Our findings will inform invasive-species risk assessments for I. typographus and D. rufipennis and highlight useful methods for predicting interactions between species that rely heavily on semiochemical communication.

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Conifer-feeding bark beetles are important herbivores and decomposers in forest ecosystems. These species complete their life cycle in nutritionally poor substrates and some can kill enormous numbers of trees during population outbreaks. The Eurasian spruce bark beetle (Ips typographus) can destroy >100 million m3 of spruce in a single year. We report a 236.8 Mb I. typographus genome assembly using PacBio long-read sequencing. The final phased assembly has a contig N50 of 6.65 Mb in 272 contigs and is predicted to contain 23,923 protein-coding genes. We reveal expanded gene families associated with plant cell wall degradation, including pectinases, aspartyl proteases, and glycosyl hydrolases. This genome sequence from the genus Ips provides timely resources to address questions about the evolutionary biology of the true weevils (Curculionidae), one of the most species-rich animal families. In forests of today, increasingly stressed by global warming, this draft genome may assist in developing pest control strategies to mitigate outbreaks.

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Key words: VKM, risk assessment, Norwegian Scientific Committee for Food and Environment, Norwegian Food Safety Authority, Norwegian Environment Agency, Biowaste, Compost, Plant health, organic waste, Phytosanitary safety, Biogas, Alien organisms Introduction The Norwegian Food Safety Authority (NFSA) and the Norwegian Environment Agency (NEA) have jointly asked the Norwegian Scientific Committee for food and environment for an assessment into treatment methods and validation methods for compost and digestate based on organic waste in relation to plant health and the spread of harmful alien organisms in Norway.  The Norwegian Food Safety Authority will use the report in its supervisory work over companies that produce compost and digestate. The assessment will also provide important input for the regulatory development of several current regulations including regulations on indicator organisms that are used to validate new methods and ensure adequate security with regards to the survival of plant pests. The Norwegian Environment Agency wants to establish whether the methods used in the composting of garden waste and other types of plant waste today are able to ensure that the finished product does not become a source for the spread of harmful alien organisms. This will form the basis for the Norwegian Environment Agency’s guidelines relating to the precautionary provisions in the regulation on alien organisms. This request is limited to an assessment of plant pests and harmful alien organisms (hereinafter alien organisms). The survival of infectious diseases harmful to people and animals is considered in separate assessments. Methods We have conducted initiating workshops for identifying relevant fundamental processes and parameters, of relevant organisms and of relevant search terms for the literature surveys, as well as for discussion and validation. Visits to composting facilities and contact with stakeholders in Norway were also conducted. This information was further implemented in an extensive literature search. This assessment include/encompass organic waste and other materials that are currently treated in biogas and composting facilities, including garden and park waste (incl. soil), plant waste from garden centres, etc., food waste and waste from the food and animal feed industry (including grain/seed husks and waste from enterprises which package and process potatoes and vegetables), manure, bulking agents used in composting facilities, and husks from contracted grain/seed cleaners for sowing. We have used a quantitative risk assessment. The level of confidence in the risk assessment is described, and uncertainties and data gaps identified. Furthermore, we have used re-submission commenting and external expert reviewing before final approval and publication. ...........

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Purpose of Review Outbreaks of tree-killing bark beetles have reached unprecedented levels in conifer forests in the northern hemisphere and are expected to further intensify due to climate change. In parts of Europe, bark beetle outbreaks and efforts to manage them have even triggered social unrests and political instability. These events have increasingly challenged traditional responses to outbreaks, and highlight the need for a more comprehensive management framework. Recent Findings Several synthesis papers on different aspects of bark beetle ecology and management exist. However, our understanding of outbreak drivers and impacts, principles of ecosystem management, governance, and the role of climate change in the dynamics of ecological and social systems has rapidly advanced in recent years. These advances are suggesting a reconsideration of previous management strategies. Summary We synthesize the state of knowledge on drivers and impacts of bark beetle outbreaks in Europe and propose a comprehensive context-dependent framework for their management. We illustrate our ideas for two contrasting societal objectives that represent the end-members of a continuum of forest management goals: wood and biomass production and the conservation of biodiversity and natural processes. For production forests, we propose a management approach addressing economic, social, ecological, infrastructural, and legislative aspects of bark beetle disturbances. In conservation forests, where non-intervention is the default option, we elaborate under which circumstances an active intervention is necessary, and whether such an intervention is in conflict with the objective to conserve biodiversity. Our approach revises the current management response to bark beetles in Europe and promotes an interdisciplinary social-ecological approach to dealing with disturbances.

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Nursery-grown Norway spruce Picea abies seedlings are often heavily attacked by the pine weevil Hylobius abietis on clear-cuts the first years after planting. Because the seedlings are not resource-limited during the growing phase in the nursery they are expected to invest less in defence than naturally regenerated seedlings already present on the clear-cuts. The latter have had to cope with various environmental stressors that could make them invest more in defence. We tested if naturally regenerated plants have stronger chemical defences than nursery-grown plants. Nursery-grown plants were planted in-between naturally regenerated plants on fresh clear cuts, and phenolic and terpene compounds in the stem bark were measured after one growing season. To test both constitutive and inducible defences, plants were either wounded, painted with methyl jasmonate (MeJA) to induce defences, or given a combination of both treatments. Growth and pine weevil attacks of the plants were registered. Nursery-grown plants had higher total concentrations of phenolic compounds and lower concentrations of terpenes than naturally regenerated plants. These opposite responses were reflected in very different compound profiles in the two plant types. We suggest the differences between plant types to be results of differences in plant age, stress level, genetic origin or possibly a combination of these factors. Most compounds showed no response to wounding, MeJA-treatment or wounding and MeJA-treatment combined, but the terpenes 3-carene, eucalyptol, limonene and para-cymene had higher concentrations in MeJA-treated nursery-grown plants than in control plants. These compounds are known to be effective in conifer resistance against weevils and bark beetles. Overall, 27% of our 400 study plants had signs of pine weevil damage after 3 ½ months in the field. However, treatment or plant type had no significant effect on whether plants were attacked or not and this might have been a result of the relatively low overall level of attacks in this study. Further studies are needed to disentangle the importance of plant age, stress level, genetic origin and resource availability for chemical defence mechanisms of young Norway spruce plants, as strengthening the natural resistance of nursery plants may be increasingly important in a future with less pesticide use.

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Overgang fra en til to generasjoner av stor granbarkbille med varmere klima vil kunne øke mengden av skader i norske skoger på grunn av to angrepsperioder. Sommertemperaturene i Norge har vært økende siden 1970-tallet og en utviklingsmodell for stor granbarkbille basert på temperatursummer viser økt hyppighet av to fullførte generasjoner i de varmeste lokalitetene de siste tiårene. Mens feltstudier og utviklingsmodellen fra Sør-Norge i den varme sommeren 1975 viste at granbarkbillen ikke rakk å fullføre en påbegynt andre generasjon, viste utviklingsmodellen full gjennomføring av to generasjoner for flere barkbilleangrepne lokaliteter i Vestfold i 2020. I disse lokalitetene observerte vi også fullt utviklete granbarkbiller under barken i november...

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The spruce bark beetle Ips typographus is the most damaging pest in European spruce forests and has caused great ecological and economic disturbances in recent years. Although native to Eurasia, I. typographus has been intercepted more than 200 times in North America and could establish there as an exotic pest if it can find suitable host trees. Using in vitro bioassays, we compared the preference of I. typographus for its coevolved historical host Norway spruce (Picea abies) and two non-coevolved (naïve) North American hosts: black spruce (Picea mariana) and white spruce (Picea glauca). Additionally, we tested how I. typographus responded to its own fungal associates (conspecific fungi) and to fungi vectored by the North American spruce beetle Dendroctonus rufipennis (allospecific fungi). All tested fungi were grown on both historical and naïve host bark media. In a four-choice Petri dish bioassay, I. typographus readily tunneled into bark medium from each of the three spruce species and showed no preference for the historical host over the naïve hosts. Additionally, the beetles showed a clear preference for bark media colonized by fungi and made longer tunnels in fungus-colonized media compared to fungus-free media. The preference for fungus-colonized media did not depend on whether the medium was colonized by conspecific or allospecific fungi. Furthermore, olfactometer bioassays demonstrated that beetles were strongly attracted toward volatiles emitted by both con- and allospecific fungi. Collectively, these results suggest that I. typographus could thrive in evolutionary naïve spruce hosts if it becomes established in North America. Also, I. typographus could probably form and maintain new associations with local allospecific fungi that might increase beetle fitness in naïve host trees.

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Nivået av granbarkbiller er økende for alle fylker i 2021, med unntak av Vest-Agder. Vestfold øker mest og har i år over 20 000 biller per felle i snitt, men billenivået er bare 69 % av nivået ved slutten av utbruddet på 1970-tallet og 75 % av nivået i 1994. Vestfold er også det området som har mest tørke- og barkbilleskader i år. Dette kan skyldes at mye tørkesvak mark har gitt ekstra mye svekkede grantrær etter tørkesommeren 2018. Videre kan en varm sommer ha gitt grunnlag for to angrepsperioder for barkbillene i stedet for en. Billenivået i øvrige fylker varierer fra 30 til 51 % av utbruddsnivået ved slutten av 1970-tallet. Det er noen skaderapporter fra kommuner i den boreonemorale sonen rundt Oslofjorden utenom Vestfold, men det er ofte uklart om skadene skyldes tørke eller barkbilleangrep. De boreale skogene i indre deler av Østlandet og i Trøndelag og Nordland har lite eller ingen tørke- og barkbilleskader i år. Videre utvikling av barkbillepopulasjoner og skader i 2022 er usikker, fordi vi ikke vet hvor mye skog som fortsatt er svekket etter tørkesommeren 2018 og som derfor kan angripes av granbarkbillen.

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Key words: VKM, risk assessment, Norwegian Scientific Committee for Food and Environment, Norwegian Food Safety Authority, biological control, Nematodes, Phasmarhabditis californica, Moraxella osloensis. Parasitic nematodes and associated bacteria are increasingly being used for biocontrol of molluscs. Functionally, it is the bacteria that kill and thus control the targeted pests, but the function of the bacteria is dependent on the nematodes, which should be regarded as vectors of biocontrol. Although the nematodes and the bacteria have a symbiotic relationship within such biocontrol formulations, it should be noted that they are not dependent on each other in the wild, but can establish separate populations which can be free-living or hosted by other organisms. The biocontrol product Nemaslug 2.0 contains the nematode Phasmarhabditis californica (strain P19D) and the bacterial symbiont Moraxella osloensis (unknown strain). The nematode was first described in 2016 and has never been reported in Norway. The lack of reports suggests that it is absent from Norway, but this conclusion comes with a high degree of uncertainty since there have been limited search efforts. The climatic thresholds of the nematode are not known, but its current distribution, spanning widely varying climates, suggests that it could survive and establish in Norway. Natural spread from currently known areas of establishment to natural habitats in Norway is ruled out due to the nematode’s limited dispersal capacity. However, human-assisted spread (e.g. via the use of biocontrol products) and establishment would be likely if Nemaslug 2.0 is allowed for use in open fields in Norway. Use of Nemaslug 2.0 in greenhouses and other enclosed areas is not likely to facilitate spread to natural habitats in Norway provided that residues are properly handled. However, deposition of product residues from greenhouses to outdoor areas may result in local establishment of the nematode in the vicinity of the deposition. Phasmarhabditis californica has a broad host range and may parasitize both rare/endangered and common mollusc species. However, there is no scientific evidence suggesting that the nematode can affect natural populations of molluscs in wild habitats, or otherwise have negative effects on biodiversity. The nematodes’ association with the bacteria Moraxella osloensis is most likely lost, or at least weakened, in natural habitats, suggesting that the nematode becomes less capable of killing its hosts in the wild. Phasmarhabditis californica is not capable of harming or infecting humans. The bacterial species Moraxella osloensis is already present in Norway in a few locations and at a low abundance, and it may be native to Norway. Little is known regarding its distribution in natural environments, but the literature shows that it can infect humans and other mammals. In humans with immunodeficiency or other comorbidities, M. osloensis can cause meningitis, vaginitis, sinusitis, bacteremia, endocarditis, and septic arthritis. The risk of infection in people handling Nemaslug 2.0 can probably be substantially reduced by protective clothing and appropriate handling. We are not aware of any reported health issues arising from use of the previous version of Nemaslug, which also contains M. osloensis. Different strains of M. osloensis are known to vary in their sensitivity to antibiotics, and likely in other traits too. Thus, the lack of information provided about the strain identity and specific characteristics of the strain used in Nemaslug 2.0 generates a high degree of uncertainty regarding its pathogenicity, climate tolerance, sensitivity to antibiotics etc.

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In 2018, up to 4 million m3 Norway spruce was killed by the spruce bark beetle Ips typographus in Sweden. The event was unique for Sweden, in terms of both affected volume and the fact that it was triggered by severe drought stress, not by ample availability of relatively defenseless storm-felled trees. The outbreak continued in 2019 and 2020, each year with twice as many trees killed as in 2018. The aim of this study was to quantify seasonal variation and potential lag-effects in tree defense capacity the year after a severe drought stress. Inoculation with a bark beetle-associated bluestain fungus, repeated four times with one-month-intervals between May and August 2019, were carried out at three field sites with spruce provenances of Swedish and East European origin representing early and late bud burst, respectively. All sites had experienced moderate to severe drought stress in 2018, and site-specific defense capacity correlated positively with the cumulative precipitation two months before inoculation. Sites with two-month precipitation levels <100 mm had larger necrotic lesions in the phloem following inoculation, an indication of lower tree defense capacity. Lesion size did not differ between provenances, and all trees were able to confine fungal infection successfully. There were some seasonal differences in necrotic lesion size, with the sites Skärsnäs and Norberg having significantly larger lesions in June than in May, and site Lugnet having large lesions also in May. Lesions were generally smaller in July and August than in June. The cross-sectional area and number of traumatic resin ducts was measured in sapwood samples from one site, Lugnet, to quantify an additional aspect of tree defenses. The area of resin ducts produced in May and June were larger than that in July and August. This is in line with a positive correlation between lesion area and resin duct area, indicating that a stronger fungal infection following inoculation in spring triggered a stronger induced defense response. The East European provenances had more resin ducts than Swedish provenances, but the area of resin ducts did not differ significantly between provenances.

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Methyl jasmonate (MeJA) treatment elicits induced resistance (IR) against pests and diseases in Norway spruce (Picea abies). We recently demonstrated using mRNA-seq that this MeJA-IR is associated with both a prolonged upregulation of inducible defenses and defense priming. Gene expression can be regulated at both a transcrip-tional and post-transcriptional level by small RNAs, including microRNAs (miRNAs). Here we explore the effects of MeJA treatment and subsequent challenge by wounding on the Norway spruce miRNA transcriptome. We found clusters of prolonged down- or upregulated miRNAs as well as miRNAs whose expression was primed after MeJA treatment and subsequent wounding challenge. Differentially expressed miRNAs included miR160, miR167, miR172, miR319, and the miR482/2118 superfamily. The most prominent mRNA targets predicted to be differentially expressed by miRNA activity belonged to the nucleotide-binding site leucine-rich repeat (NBS- LRR) family. Among other predicted miRNA targets were genes regulating jasmonic acid biosynthesis. Our re-sults indicate that miRNAs have an important role in the regulation of MeJA-IR in Norway spruce.

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Skogen i Norge har et årlig netto opptak i underkant av 30 mill. tonn CO2. Størrelsen på opptaket påvirkes av forvaltningen av skogarealene, både gjennom endringer i totalarealet (avskoging og påskoging), og forvaltningen av de eksisterende skogarealene. I denne rapporten presenteres en første vurdering av syv klimatiltak som ikke tidligere er utredet, en kunnskapsoppdatering av noen tidligere utredede klimatiltak, og en framskrivning av mulige effekter på netto CO2-opptak av ulike nivå på implementerte tiltak. Rapporten er skrevet på bestilling fra Landbruksdirektoratet og Miljødirektoratet, og det er direktoratene som har gjort utvalget av tiltak....

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In response to various stimuli, plants acquire resistance against pests and/or pathogens. Such acquired or induced resistance allows plants to rapidly adapt to their environment. Spraying the bark of mature Norway spruce (Picea abies) trees with the phytohormone methyl jasmonate (MeJA) enhances resistance to tree‐killing bark beetles and their associated phytopathogenic fungi. Analysis of spruce chemical defenses and beetle colonization success suggests that MeJA treatment both directly induces immune responses and primes inducible defenses for a faster and stronger response to subsequent beetle attack. We used metabolite and transcriptome profiling to explore the mechanisms underlying MeJA‐induced resistance in Norway spruce. We demonstrated that MeJA treatment caused substantial changes in the bark transcriptional response to a triggering stress (mechanical wounding). Profiling of mRNA expression showed a suite of spruce inducible defenses are primed following MeJA treatment. Although monoterpenes and diterpene resin acids increased more rapidly after wounding in MeJA‐treated than control bark, expression of their biosynthesis genes did not. We suggest that priming of inducible defenses is part of a complex mixture of defense responses that underpins the increased resistance against bark beetle colonization observed in Norway spruce. This study provides the most detailed insights yet into the mechanisms underlying induced resistance in a long‐lived gymnosperm.

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Plants can form an immunological memory known as defense priming, whereby exposure to a priming stimulus enables quicker or stronger response to subsequent attack by pests and pathogens. Such priming of inducible defenses provides increased protection and reduces allocation costs of defense. Defense priming has been widely studied for short‐lived model plants such as Arabidopsis, but little is known about this phenomenon in long‐lived plants like spruce. We compared the effects of pretreatment with sublethal fungal inoculations or application of the phytohormone methyl jasmonate (MeJA) on the resistance of 48‐year‐old Norway spruce (Picea abies) trees to mass attack by a tree‐killing bark beetle beginning 35 days later. Bark beetles heavily infested and killed untreated trees but largely avoided fungus‐inoculated trees and MeJA‐treated trees. Quantification of defensive terpenes at the time of bark beetle attack showed fungal inoculation induced 91‐fold higher terpene concentrations compared with untreated trees, whereas application of MeJA did not significantly increase terpenes. These results indicate that resistance in fungus‐inoculated trees is a result of direct induction of defenses, whereas resistance in MeJA‐treated trees is due to defense priming. This work extends our knowledge of defense priming from model plants to an ecologically important tree species.

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Key words: VKM, risk assessment, Norwegian Scientific Committee for Food and Environment, Norwegian Environment Agency, mycorrhiza. Mycorrhiza is a beneficial association between plant roots and fungi. This mutualistic symbiosis is essential for plant growth in most natural terrestrial ecosystems and in agriculture. Commercial mycorrhizal products containing fungi and bacteria may promote plant growth, especially on sites without a natural microbial community. Due to the risk of unintended negative effects, introduction of new species or genetically different isolates of native species should always be considered carefully. This report assesses the risk of establishment and spread of six fungal species and six bacterial species included in different commercial mycorrhizal products, as well as the species’ potential impact on Norwegian biodiversity. Most of the evaluated fungi and bacteria are probably present in Norway, even though presence at present data only exist for two of the six fungal species. Establishment of the assessed fungi on the plants and sites where they are applied is considered moderately likely, with medium uncertainty, while establishment of the bacterial species is considered to range from very unlikely to very likely depending on the bacterial group, with low uncertainty. The probability of spread to the wider environment ranges from unlikely (four fungal species), to moderately likely (two fungal species), to very likely (five of the six bacterial species). However, for all species it is considered unlikely that establishment and spread would have negative effects on other native species, habitats and ecosystems in Norway.

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ANDERcontrol with the predatory mite Amblyseius andersoni as the active organism is sought to be used as a biological control agent in Norway. ANDERcontrol is intended for use against different mites (such as the two-spotted, fruit-tree, and red spider mite, russet mite,cyclamen mite) and in horticultural crops such as fruits, berries, vegetables, and ornamental. VKM’s conclusions are as follows Prevalence, especially if the organism is found naturally in Norway: Amblyseius andersoni has not been observed in Norway. It has been observed, in low numbers, in southern Sweden and has the capability to enter diapause under unfavourable conditions which suggests the potential for establishing under Norwegian conditions. It is however, the view of VKM that it likely lacks the ability to survive and establish in areas with cold winters and chilly summers, as found in most parts of Norway under current climatic conditions. The potential of the organism for establishment and spread under Norwegian conditions specified for use in greenhouses and open field: The thermal preference of A. andersoni restricts its establishment, and the species has not been observed in Norway. The species is capable of entering diapause, but the lack of records, despite targeted surveys, makes it the opinion of VKM that it is unlikely that A. andersoni will be able to establish in outdoor areas in Norway. However, the lack of information on temperature tolerance of the species constitute an uncertainty factor. The risk of spread from greenhouses is low because no wind or vector are likely to carry the mites from the greenhouse to suitable outdoor habitats, and mite populations in greenhouses do not enter the more cold-tolerant diapause. All conclusions are uncertain due to lack of relevant information regarding the species’ climate tolerance. Any ambiguities regarding the taxonomy, which hampers risk assessment: There are no taxonomic challenges related to the assessment of A. andersoni. Assessment of the product and the organism with regard to possible health risk: VKM is unaware of reports where harm to humans by A. andersoni itself, or associated pathogenic organisms have been observed. Mites may however produce allergic reactions in sensitive individuals handling plant material with high numbers of individuals. There is reason to believe that this holds true also for A. andersoni. Key words: VKM, risk assessment, Norwegian Scientific Committee for Food and Environment, Norwegian Food Safety Authority, biological control, predatory mite

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The product Limonica, with the predatory mite Amblydromalus limonicus as the active organism, is sought to be used as a biological control agent in Norway. Limonica is intended for use against western flower thrips (Frankliniella occidentallis), other thrips (e.g. Thrips tabaci), spider mites and whiteflies (e.g. Trialeurodes, Aleyrodes and Bemisia spp.) in protected horticultural crops such as cucumber, sweet pepper, strawberry and ornamentals. The product is not recommended for greenhouse-grown tomatoes. VKM’s conclusions are as follows Distribution, especially if the organism is found naturally in Norway Amblydromalus limonicus has a very wide natural distribution, being reported from New Zealand, Australia South America, Central America, and North America as well as Hawaii. It has also recently established populations in crop productions and non-crop vegetation in Catalonia, North Eastern Spain. Amblydromalus limonicus have not been observed in Norway. The species seems not to have the capability to enter diapause under unfavourable conditions and it is the view of VKM that it likely lacks the ability to survive and establish in areas with cold winters and chilly summers, as found in most parts of Norway under current climatic conditions. The potential of the organism for establishment and spread under Norwegian conditions specified for use in greenhouses and open field The thermal preference of A. limonicus restricts its establishment, and the species has not been observed outdoors in Norway. As the species is incapable of entering diapause it is the opinion of VKM that it is unlikely that A. limonicus will be able to establish in outdoor areas in Norway. However, the lack of detailed information on temperature tolerance of the species constitutes an uncertainty factor. The risk of spread from greenhouses is low because no wind or vector are likely to carry the mites from the greenhouse to suitable outdoor habitats. However, mites that have escaped from a greenhouses to may spread in the nature. All conclusions are uncertain due to lack of relevant information regarding the species’ climate tolerance. Its origin and current distribution suggest that it cannot survive cold winters. Any ambiguities regarding taxonomy that hamper risk assessment There are no taxonomic challenges related to the assessment of A. limonicus. Assessment of the product and the organism with regard to possible health risks VKM Report 2020: 13 8 VKM is unaware of reports where harm to humans has been observed, whether by A. limonicus itself. Mites may, however, produce allergic reactions in sensitive individuals handling plant material with high numbers of individuals. There is reason to believe that this holds true also for A. limonicus. Key words: VKM, risk assessment, Norwegian Scientific Committee for Food and Environment, Norwegian Food Safety Authority, biological control, predatory mite

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Atheta-System with the rove beetle Atheta coriaria (Kraatz 1856) as the active organism is sought to be used as a biocontrol agent for augmentation biological control in Norway. Atheta-System is intended for use against soil dwelling stages of fungus gnats (e.g. Bradysia paupera), shore flies (Scatella stagnalis), and thrips (e.g. Frankliniella occidentallis) in greenhouses, plastic tunnels, and other closed or controlled climate cultivations of horticultural crops, incl. soft-fruit crops, vegetables, ornamentals, and kitchen herbs. VKM’s conclusions are as follows Distribution, especially if the organism is found naturally in Norway Atheta coriaria is established (naturalized) in Norway since 1919 and has been reported numerous times from Agder in the South to Trøndelag in mid-Norway. The potential of the organism for establishment and spread under Norwegian conditions specified for use in greenhouses and open field The thermal thresholds of A. coriaria are not well-studied, but its current distribution in Southern and mid-Scandinavia shows that it tolerates relatively low winter temperatures, and that the Norwegian summer climate allows for successful reproduction. A. coriaria overwinters in the soil, which provides a relatively sheltered environment. Adults disperse rapidly by flying. All life stages can be vectored by humans – mainly by movement of soil and compost material. Thus, further spread northwards in Norway is predicted irrespective of additional introductions. It is unknown if it can enter diapause under greenhouse conditions. Any ambiguities regarding the taxonomy which hamper risk assessment There are no major taxonomic challenges related to the assessment of A. coriaria. Assessment of the product and the organism with regard to possible health risk VKM is unaware of reports of harm inflicted to humans by A. coriaria itself. Atheta-System comes with the cosmopolitan cheese mite (Tyrophagus putrescentiae), serving as food for A. coriaria. As with most mites, T. putrescentiae may induce allergic reactions in sensitive persons handling the product. Key words: VKM, risk assessment, Norwegian Scientific Committee for Food and Environment, Norwegian Food Safety Authority, biological control, rove beetle

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Tree-killing bark beetles are the most economically important insects in conifer forests worldwide. However, despite >200 years of research, the drivers of population eruptions and crashes are still not fully understood and the existing knowledge is thus insufficient to face the challenges posed by the Anthropocene. We critically analyze potential biotic and abiotic drivers of population dynamics of an exemplary species, the European spruce bark beetle (ESBB) (Ips typographus) and present a multivariate approach that integrates the many drivers governing this bark beetle system. We call for hypothesis-driven, large-scale collaborative research efforts to improve our understanding of the population dynamics of this and other bark beetle pests. Our approach can serve as a blueprint for tackling other eruptive forest insects.

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Convergent evolution of semiochemical use in organisms from different Kingdoms is a rarely described phenomenon. Tree-killing bark beetles vector numerous symbiotic blue-stain fungi that help the beetles colonize healthy trees. Here we show for the first time that some of these fungi are able to biosynthesize bicyclic ketals that are pheromones and other semiochemicals of bark beetles. Volatile emissions of five common bark beetle symbionts were investigated by gas chromatography-mass spectrometry. When grown on fresh Norway spruce bark the fungi emitted three well-known bark beetle aggregation pheromones and semiochemicals (exo-brevicomin, endo-brevicomin and trans-conophthorin) and two structurally related semiochemical candidates (exo-1,3-dimethyl-2,9-dioxabicyclo[3.3.1]nonane and endo-1,3-dimethyl-2,9-dioxabicyclo[3.3.1]nonane) that elicited electroantennogram responses in the spruce bark beetle Ips typographus. When grown on malt agar with 13C D-Glucose, the fungus Grosmannia europhioides incorporated 13C into exo-brevicomin and trans-conophthorin. The enantiomeric compositions of the fungus-produced ketals closely matched those previously reported from bark beetles. The production of structurally complex bark beetle pheromones by symbiotic fungi indicates cross-kingdom convergent evolution of signal use in this system. This signaling is susceptible to disruption, providing potential new targets for pest control in conifer forests and plantations.

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Several studies have looked at how individual environmental factors influence needle morphology in conifer trees, but interacting effects between drought and canopy position have received little attention. In this study, we characterized morphological responses to experimentally induced drought stress in sun exposed and shaded current-year Norway spruce needles. In the drought plot trees were suffering mild drought stress, with an average soil water potential at 50 cm depth of -0.4 MPa. In general, morphological needle traits had greater values in sun needles in the upper canopy than in shaded needles in the lower canopy. Needle morphology 15 months after the onset of drought was determined by canopy position, as only sun needle morphology was affected by drought. Thus, canopy position was a stronger morphogenic factor determining needle structure than was water availability. The largest influence of mild drought was observed for needle length, projected needle area and total needle area, which all were reduced by ~27% relative to control trees. Needle thickness and needle width showed contrasting sensitivity to drought, as drought only affected needle thickness (10% reduction). Needle dry mass, leaf mass per area and needle density were not affected 15 months after the onset of mild drought. Our results highlight the importance of considering canopy position as well as water availability when comparing needle structure or function between conifer species. More knowledge about how different canopy parts of Norway spruce adapt to drought is important to understand forest productivity under changing environmental conditions.

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Plants are exposed to various pathogens in their environment and have developed immune systems with multiple defense layers to prevent infections. However, often pathogens overcome these resistance barriers, infect plants and cause disease. Pathogens that cause diseases on economically important crop plants incur huge losses to the agriculture industry. For example, the 2016 outbreak of strawberry grey mold (Botrytis cinerea) in Norway caused up to 95% crop losses. Such outbreaks underline the importance of developing novel and sustainable tools to combat plant diseases, for example by increasing the plants’ natural disease resistance. Priming plant defenses using chemical elicitors may enhance resistance against multiple pathogens. Such an approach may reduce the use of chemical fungicides and pesticides that often select for resistant strains of pests and pathogens. My presentation will focus on the effectiveness of different chemical agents to prime woodland strawberry (Fragaria vesca) defenses against the necrotroph B. cinerea. We have identified several genes that seem to play a role in disease resistance in strawberry and associated epigenetic memory mechanisms. Our results point out new management avenues for more sustainable crop protection schemes.

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I Europa er det registrert økende omfang av skogskader de siste hundre år, og klimaendringer er identifisert som en viktig driver bak økningene i for eksempel vindskader, barkbilleangrep og skogbranner. Det er likevel store regionale forskjeller i Europa, med en tendens til økt vekst og produktivitet i nordlige og høyereliggende skogområder, og mer tørkestress og mortalitet i sør. Ikke are endringer i klima, men også endringer i skogskjøtsel og skogstruktur påvirker forekomsten av skader i skog...

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As primary producers, plants are under constant pressure to defend themselves against potentially deadly pathogens and herbivores. In this review, we describe short- and long-term strategies that enable plants to cope with these stresses. Apart from internal immunological strategies that involve physiological and (epi)genetic modifications at the cellular level, plants also employ external strategies that rely on recruitment of beneficial organisms. We discuss these strategies along a gradient of increasing timescales, ranging from rapid immune responses that are initiated within seconds to (epi)genetic adaptations that occur over multiple plant generations. We cover the latest insights into the mechanistic and evolutionary underpinnings of these strategies and present explanatory models. Finally, we discuss how knowledge from short-lived model species can be translated to economically and ecologically important perennials to exploit adaptive plant strategies and mitigate future impacts of pests and diseases in an increasingly interconnected and changing world.

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Yunnan pine is the most important tree species in SW China in both economical and ecological terms, but it is often killed by pine shoot beetles (Tomicus spp.). Tomicus beetles are secondary pests in temperate regions and the aggressiveness of the beetles in SW China is considered to be due to the warm subtropical climates as well as the beetles’ virulent fungal associates. Here, we assessed the virulence of three blue-stain fungi (Leptographium wushanense, L. sinense and Ophiostoma canum) associated with pine shoot beetles to Yunnan pine (Pinus yunnanensis) in SW China. Following fungal inoculation, we measured necrotic lesion lengths, antioxidant enzyme activities and monoterpene concentrations in the stem phloem of Yunnan pine. Leptographium wushanense induced twice as long lesions as L. sinense and O. canum, and all three fungi induced significantly longer lesions than sterile agar control inoculations. The activity of three tested antioxidant enzymes (peroxidase, polyphenol oxidase, and superoxide dismutase) increased after both fungal inoculation and control inoculation. However, L. wushanense and L. sinense generally caused a greater increase in enzyme activities than O. canum and the control treatment. Fungal inoculation induced stronger increases in six major monoterpenes than the control treatment, but the difference was significant only for some fungus-monoterpene combinations. Overall, our results show that L. wushanense and L. sinense elicit stronger defense responses and thus are more virulent to Yunnan pine than O. canum. The two Leptographium species may thus contribute to the aggressiveness of their beetle vectors and could damage Yunnan pine across SW China if they spread from the restricted geographical area they have been found in so far.

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Climate change is one of the greatest challenges for the biosphere. As sessile organisms, plants must adapt quickly to keep pace with the rapidly changing climatic conditions. Epigenetic memory is one mechanism which would provide sufficient plasticity under rapid climate change and enable long-lived organisms to survive long enough to adapt by classical genetic selection. In Norway spruce, the timing of bud burst and bud set are regulated by an epigenetic memory established by the temperature sum endured during embryogenesis. The resulting epitypes display a life-long shift in seasonal timing of the bud phenology, a trait previously presumed to be under strict classical selection and highly heritable. However, Norway spruce is a difficult plant to study because it has a very long generation time and an extensive genome size. We therefore seek to find a suitable perennial model plant to study the phenomenon of epigenetic climatic memory. Woodland strawberry (Fragaria vesca) may be an ideal model to research the role of epigenetic memory on plant phenology. Fragaria vesca is a perennial plant with a small well-characterized genome, a short sexual reproduction cycle and can also propagate asexually trough clonal daughter plants formed by stolons. We will explore whether the temperature sum experienced during sexual and asexual reproduction impact on the phenology of Fragaria vesca and use this as a model to decipher the molecular mechanism underlying epigenetic memory in plants.

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Bark beetles and their symbiotic bluestain fungi kill more trees than all other natural factors and cause great economic losses in Norway spruce and other conifers. The tree's natural defenses are the most important factor maintaining bark beetle-fungus complexes at low, endemic levels. Spraying Norway spruce trees with the plant hormone methyl jasmonate (MeJA) primes tree defenses without eliciting notable induced defenses, but enables the trees to respond much more quickly and strongly when challenged by bark beetles or fungi several weeks after treatment. This phenomenon, known as defense priming, is a form of acquired resistance that enables cost-effective and vigorous defense responses. In field experiments with 50-year-old clonal spruce trees terpene concentrations in the bark increased 60-fold within 24 h after mechanical wounding of MeJA primed trees, compared with a 13-fold increase in unprimed control trees. We also observed altered transcriptional patterns in primed trees using Illumina deep transcriptome sequencing. When wounded, primed trees launched vigorous induced defenses with significant differential regulation of gene transcripts, such as those involved in phenylpropanoid synthesis leading to lignification. Resistance-like genes, such as the NB-LRR coding genes, are also more rapidly induced in primed than in unprimed trees. Transcriptome results from primed but unwounded trees indicate an alteration in the state of the chromatin, resembling changes associated with the activity of the epigenetic machinery creating long-lasting epigenetic marks. We do not know yet how long the primed state is activated in Norway spruce, but our data so far indicate that it may last for at least 3 years.

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The bark beetle Ips typographus carries numerous fungi that could be assisting the beetle in colonizing live Norway spruce (Picea abies) trees. Phenolic defenses in spruce phloem are degraded by the beetle's major tree-killing fungus Endoconidiophora polonica, but it is unknown if other beetle associates can also catabolize these compounds. We compared the ability of five fungi commonly associated with I. typographus to degrade phenolic compounds in Norway spruce phloem. Grosmannia penicillata and Grosmannia europhioides were able to degrade stilbenes and flavonoids faster than E. polonica and grow on minimal growth medium with spruce bark constituents as the only nutrients. Furthermore, beetles avoided medium amended with phenolics but marginally preferred medium colonized by fungi. Taken together our results show that different bark beetle-associated fungi have complementary roles in degrading host metabolites and thus might improve this insect's persistence in well defended host tissues.

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Plants are exposed to various pathogens in their environment and have developed immune systems with multiple layers of defence to fight-back. However, often pathogens overcome the resistance barriers, infect the plants to cause the disease. Pathogens that cause diseases on economically important crop plants like strawberry incur huge losses to the agriculture industry. For example, The 2016 outbreak of strawberry grey mould (Botrytis cinerea) in Norway caused up to 95% crop losses. Outbreaks like this underline the importance of developing novel and sustainable tools to combat plant diseases, for example by increasing the plants’ natural disease resistance. Priming plant defences using chemical elicitors may be effective in providing the enhanced resistance against multiple pathogens. We have used β-aminobutyric acid (BABA) as a chemical priming agent to induce resistance in Fragaria vesca against Botrytis cinerea. Effects of BABA on disease progression and defence responses of Fragaria are being characterized using molecular tools like RNAseq, RT-PCR and ChIP. As priming chemicals may induce an epigenetic memory in treated plants, we also plan to study the histone methylation patterns in primed plants and the genes that are regulated. Our long-term aim is to understand the duration of the epigenetic memory and its cross-generational transmission to the progeny in Fragaria. Our results will help guide various crop protection strategies in addition to providing new insights to develop novel tools for plant disease management.

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1 The European spruce bark beetle Ips typographus is a damaging pest on spruce in Europe. Beetle interactions with tree species originating outside the natural range of the beetle are largely unknown and may be unpredictable because trees without a co-evolutionary history with the beetle may lack effective defences. 2 The terpenoid composition and breeding suitability for I. typographus of the historic host Norway spruce Picea abies were compared with two evolutionary naïve spruces of North American origin that are extensively planted in North-West Europe: Sitka spruce Picea sitchensis and Lutz spruce Picea glauca x lutzii. 3 The bark of all three species had a similar chemical composition and similar levels of total constitutive terpenoids, although Norway spruce had higher total induced terpenoid levels. 4 Beetles tunnelling in the three spruce species produced similar amounts of aggregation pheromone. Controlled breeding experiments showed that I. typographus could produce offspring in all three species, with a similar offspring length and weight across species. However, total offspring production was much lower in Sitka and Lutz spruce. 5 Overall, the results of the present study suggest that I. typographus will be able to colonize Sitka and Lutz spruce in European plantations and in native spruce forests in North America if introduced there.

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Global warming will most likely lead to increased drought stress in forest trees. We wanted to describe the adaptive responses of fine roots and fungal hyphae, at different soil depths, in a Norway spruce stand to long-term drought stress induced by precipitation exclusion over two growing seasons. We used soil cores, minirhizotrons and nylon meshes to estimate growth, biomass and distribution of fine roots and fungal hyphae at different soil depths. In control plots fine roots proliferated in upper soil layers, whereas in drought plots there was no fine root growth in upper soil layers and roots mostly occupied deeper soil layers. Fungal hyphae followed the same pattern as fine roots, with the highest biomass in deeper soil layers in drought plots. We conclude that both fine roots and fungal hyphae respond to long-term drought stress by growing into deeper soil layers.

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Utstillingen «Det fantastiske treet» forteller om hvordan treet blir til, og at fotosyntesen er grunnlaget for alt liv. Bladene er verdens beste solfangere, og vi forteller hvordan fotosyntesen skjer i bladet. Trærnes magiske evne til å forvandle luft til sukker forklares på en ny og spennende måte. For å vise hvor spektakulær fotosyntesen er har vi lagd en 9 meter lang lysende akrylvegg som viser snittet av et blad. Midt i utstillingen står en 7,5 meter høy treskulptur laget av 10 km aluminiumsrør – selve Det fantastiske treet. Det fantastiske treeter et godt eksempel på forskningsformidling og et fruktbart samarbeid mellom to institusjoner. Norsk institutt for bioøkonomi (NIBIO) ved Skog og utmarksdivisjonen (tidligere Skog og landskap) har gjort et stort og omfattende arbeid med å tilgjengeliggjøre forskning og kvalitetssikre innholdet i utstillingen. NIBIO har vært en uvurdelig støttespiller i den faglige kvalitetssikringen. Vi har lagd en utstilling som skal overbevise publikum om hvilken spektakulær prosess fotosyntesen er og at det ikke er «bare bare» å bli et stort tre. Publikum skal både fascineres, og de skal få ny kunnskap. Den skal også vekke nysgjerrigheten for spennende forskning og alle ubesvarte spørsmål vi har rundt skogen og treet – det er fremdeles mye vi ikke vet!

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Kva hadde vel julaan vore utan eit grønt, glitrande juletre? Men det er ikkje ei sjølvfølgje at julegran kan hoggast alle stadar i Noreg. Grana er nemleg eit utsett treslag som er i ein stadig kamp mot insekt og sopp for å overleve. Heldigvis har grana nokre overraskande knep i bakhand som sender fiendane på dør, fortel seniorforskar og granekspert Paal Krokene frå Norsk institutt for bioøkonomi (NIBIO).

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The purpose of this study is to increase the basic understanding of outbreak dynamics in order to improve the management of bark beetle outbreaks. The spruce bark beetle Ips typographus is a major disturbance agent of European forests and is the continent’s most economically and environmentally damaging bark beetle. Outbreaks of the spruce bark beetle are often triggered by large windfall episodes, and we have utilized a unique opportunity to study a Slovakian outbreak where little salvage logging was performed in some areas after a 2.5 million m3 storm-felling in 2004. Our analyses focused on the first five years after the windfall, and we used a combination of empirical data and simulation models to understand the spatial patterns of beetle-killed forest patches developing during the outbreak. The univoltine beetle population used an increasing proportion of the windfelled trees during the two first seasons after the storm, but from the third season onwards our comparisons of inter-patch distance distributions indicated a transition from beetle production largely in windfall areas to a self-sustaining outbreak with infestation patches developing independently of the windthrows. The size of new infestation patches formed after this transition was modeled as a function of beetle pressure, estimated by the proportion of a circle area surrounding new patches that was covered by infestation patches the previous year. Our model results of patch size distribution did not correspond well with the empirical data if patch formation was modeled as a pure dispersal–diffusion process. However, beetle aggregation on individual trees appears to be important for patch development, since good correspondence with empirical data was found when beetle aggregation was incorporated in the modeled dispersal process. The strength of correspondence between the beetle aggregation model and the empirical data varied with the density of aggregation trees in the modeled landscape, and reached a maximum of 83% for a density of three aggregation trees per infestation patch. Our results suggest that efficient removal of windfelled trees up until the start of the second summer after a major windfall is important to avoid a transition into a patch-driven bark beetle outbreak that is very difficult to manage. Our results also indicate that the outcome of a patch-driven outbreak is difficult to predict, since the development of new infestation patches is not a simple function of beetle pressure but is also affected by beetle behavior and local forest conditions.

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Increasing inter-continental trade with wood chips represents a challenge for phytosanitary authorities, as such trade may lead to pest introductions and invasions with huge impacts on forest ecosystems and economy. Predicting species invasions and their impacts in advance may be difficult, but improved information about potential invasive species ahead of any interceptions is an important precautionary step to reduce the probability of invasions. Here we identify bark- and wood-boring insects that have a potential to become invasive in northern Europe, and that may be introduced by import of deciduous wood chips from North America. The potentially most damaging species belong to the beetle genus Agrilus (Buprestidae), which includes the highly damaging emerald ash borer A. planipennis. We give a brief presentation of this and seven other Agrilus species or subspecies, and review factors of importance for the risk of establishment and potential economic and ecological impacts of these species. We also discuss one Scolytinae, Hylurgopinus rufipes. There are strong indications in the literature that some north European trees are highly susceptible to attack from the selected beetle species. We therefore conclude that because north European trees have not coevolved with these herbivores and thus may lack adequate defenses, most of the identified beetle species are likely to spread in “defense- and enemy-free space” if they are introduced to northern Europe, with considerable economic and ecological consequences.

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Trees must respond to many environmental factors during their development, and light is one of the main stimuli regulating tree growth. Thinning of forest stands by selective tree removal is a common tool in forest management that increases light intensity. However, morphological and anatomical adaptations of individual shoots to the new environmental conditions created by thinning are still poorly understood. In this study, we evaluated shoot morphology (shoot length, needle number, projected leaf area) and anatomy (tracheid lumen area, tracheid number, tracheid dimensions, xylem area, potential hydraulic conductivity) in three Norway spruce (Picea abies/L./Karst.) families exposed to different thinning regimes. We compared shoot characteristics of upper-canopy (i.e. sun-exposed) and lower-canopy (i.e. shaded) current-year shoots in a control plot and a plot thinned to 50 % stand density the previous year. One tree per family was chosen in each treatment, and five shoots were taken per canopy position. We found that upper-canopy shoots in both plots had higher values than lower-canopy shoots for all studied parameters, except lumen roundness and tracheid frequency (i.e. tracheid number per xylem area). Thinning had little effect on shoot morphology and anatomy 1 year after thinning, except for small but significant changes in tracheid dimensions. Needles were more sensitive to altered light conditions, as projected leaf area of shoot, needle number and leaf hydraulic conductivity changed after thinning. Differences between upper- and lower-canopy shoots did not seem to be influenced by thinning and were almost the same in both plots. Our results suggest that lower-canopy shoots require several years to modify their morphology and anatomy to new light conditions following thinning. The slow light adaptation of the lower canopy may be of practical importance in forest management: thinned stands may be predisposed to drought stress because newly exposed shoots experience increased illumination and transpiration after thinning.

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Bark beetles and associated fungi are among the greatest natural threats to conifers worldwide. Conifers have potent defenses, but resistance to beetles and fungal pathogens may be reduced if tree stored resources are consumed by fungi rather than used for tree defense. Here, we assessed the relationship between tree stored resources and resistance to Ceratocystis polonica , a phytopathogenic fungus vectored by the spruce bark beetle Ips typographus. We measured phloem and sapwood nitrogen, non-structural carbohydrates (NSC), and lipids before and after trees were attacked by I. typographus (vectoring C. polonica) or artificially inoculated with C. polonica alone. Tree resistance was assessed by measuring phloem lesions and the proportion of necrotic phloem around the tree’s circumference following attack or inoculation. While initial resource concentrations were unrelated to tree resistance to C. polonica, over time, phloem NSC and sapwood lipids declined in the trees inoculated with C. polonica. Greater resource declines correlated with less resistant trees (trees with larger lesions or more necrotic phloem), suggesting that resource depletion may be caused by fungal consumption rather than tree resistance. Ips typographus may then benefit indirectly from reduced tree defenses caused by fungal resource uptake. Our research on tree stored resources represents a novel way of understanding bark beetle-fungal-conifer interactions.

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Insects are among the organisms that will react most rapidly to climate change. They have a short generation span, they are very mobile, and their rate of development is directly impacted by temperature. This means that the development from egg to adult insect is much quicker when temperatures rise – a fact that may bode bad news for forestry.

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This chapter provides an overview of anatomical and ecological aspects of resin-based defences in pines and contrasts the defence strategy of pines with that of other conifers. The main constituents of conifer resin are mono- and diterpenes in about equal amounts, with smaller amounts of sesquiterpenes. Resin production and storage represent a great cost for the trees, and because resin is both chemically toxic and physically deterring to insects and pathogens it has long been considered an important defence mechanism in conifers. Preformed or constitutive resin structures are present in pines and all other members of the pine family, but are generally absent in non-Pinaceae species. Resin stored under pressure in constitutive ducts flows out when a tree is injured and helps trapping or repelling invading organisms and sealing the wound. Pines have constitutive resin ducts in needles, phloem and xylem. In the phloem and xylem constitutive resin ducts are oriented both radially (within the radial rays) and axially in the form of cortical resin ducts in the outer phloem and constitutive resin ducts in the xylem. Numerous connections between the radial resin ducts and the axial resin ducts in the xylem create a large inter-connected resin reservoir. In addition, so-called traumatic resin ducts can be induced axially in the xylem in response to wounding, insect attack or other biotic and abiotic stresses. Traumatic resin ducts may contribute to so-called acquired or systemic induced resistance that increases tree resistance to future attacks.

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Stormen Dagmar som rammet Sør-Norge i romjula blåste ned mye skog. Dersom de vindfelte trærne blir liggende i skogen gjennom sommeren er det stor fare for at barkbillene vil oppformere seg i vindfallet. I granskog kan dette føre til omfattende angrep på den skogen som i dag er frisk.

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We compared gene expression in Norway spruce secondary phloem (bark) and developing xylem (sapwood) in response to the necrotrophic pathogen Heterobasidion parviporum, wounding and methyl jasmonate (MeJ). The pathogen induced systemic and local up-regulation of PaPX3, PaPX2 and PaChi4 in both bark and sapwood that returned to constitutive levels as the plants recovered from the infection, whereas the local responses to MeJ were similar in both tissues but was longer lasting for PaPX3 and PaChi4. Genes involved in lignin biosynthesis (PaPAL1, PaPAL2, PaC4H3/5 and PaHCT1) were up-regulated locally in the bark in response to pathogen and wounding whereas MeJ induced a similar but stronger local response. The ethylene biosynthesis related transcripts PaACO and PaACS did not increase in response to MeJ treatment or the pathogen, however it increased both locally and systemically as a response to wounding in the sapwood. These results demonstrate that the local and systemic host responses to pathogen infection and wounding largely correspond and reveal striking similarities between the local response to a necrotroph, wounding and MeJ treatment in both bark and living wood.

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Purpose: Drought-induced tree susceptibility is a major risk associated with climate change. Here we report how an 11-week drought affected tracheid structure, gene expression, and above- and belowground growth in 5-year-old Norway spruce trees (Picea abies) under controlled conditions. Results: The canopy of trees subjected to severe drought had significantly less current-year needle biomass, and fewer tracheids and tracheid rows in current-year shoots compared to fully watered control trees. Belowground tissues were more strongly affected by drought than aboveground tissues. In fine roots (<2 mm diameter) severe drought significantly reduced root biomass, root diameter, root length density and root surface area per soil volume compared to the control. Tracheid diameter and hydraulic conductivity in fine roots were significantly lower and tracheid flatness higher in trees subjected to severe drought than in control trees, both for long and short roots. Transcripts of the drought-related dehydrins PaDhn1 and PaDhn6 were strongly upregulated in stem bark and current-year needles in response to drought, whereas PaDhn4.5 was down-regulated. Conclusions: This study demonstrates that drought reduces biomass and hydraulic conductivity in fine roots and needles. We suggest that the ratio between PaDhn6 and PaDhn4.5 may be a sensitive marker of drought stress in Norway spruce.

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Ceratocystis polonica and Heterobasidion parviporum are important fungal pathogens in Norway spruce (Picea abies). Tree susceptibility to these pathogens with respect to phenology was studied using artificial fungal inoculations at six stages of bud development, and assessed by measuring phloem necroses in the stems of 2- and 8-year-old trees. Tree capacity for resistance was assessed by measuring phloem nonstructural carbohydrates at each stage. Phloem necroses were significantly larger in trees with fungal versus control inoculations and increased significantly over time. Changes in nonstructural carbohydrates occurred in the trees; a significant decline in starch and a slight but significant increase in total sugars occurred over time. These results suggest that susceptibility to fungal pathogens and carbohydrate levels in the stems of the trees were related to fine-scale changes in bud development. A trade-off may occur between allocation of starch (the major fraction of the stem carbohydrate pool) to bud development/shoot growth versus defence of the stem. Previous tests of plant defence hypotheses have focused on herbivory on plants growing under different environmental conditions, but the role of phenology and the effect of pathogens are also important to consider in understanding plant resource allocation patterns.