Acute Oak Decline Research Articles

Oak declines: Reviewing the evidence for causes, management implications and research gaps

Abstract Oak decline is a complex disorder caused by multiple stressors. Although declines have been observed across Europe since 1700, there is still a lot of uncertainty around the cause, and therefore the appropriate management techniques. Using literature from across European oak ecosystems, this review and perspective discusses the key stressors associated with oak declines in Quercus robur L. and Q. petraea (Matt.) Liebl. in Europe and the newly described acute oak decline breaking out in the United Kingdom (and beyond), with a view to identifying important evidence gaps and management implications. The key factors implicated in oak decline include drought, pests and pathogens. These factors can interact in positive feedback loops to increase stress and decline within oaks. Extreme frost, waterlogging, soil properties, land management, nitrogen pollution, heavy metal pollution, genetic predisposition and mycorrhizal changes could also be involved in decline, but more research is required to understand these. In acute oak decline, necrotic lesions are caused by a bacterial complex of up to three species, and it has been observed that the presence of the wood borer Agrilus biguttatus Fabricius 1776 can amplify the symptoms. Practical implication: The amount that each stressor contributes towards these declines and the ‘tipping points’ are largely unknown and are likely to differ between decline events, sites and even individual trees. This makes management advice provision exceedingly difficult. Historic records show oaks in decline can recover; therefore, allowing trees time and space to recover should be a priority for management practitioners. Future research recommendations for effective management of declining oaks are discussed.

Assessment of Acute Oak Decline in Latvia

Acute Oak Decline (AOD) is a complex disease affecting oaks (Quercus spp.). Typical symptoms include a dark, sticky exudate from bark cracks. Larval galleries of the beetle Agrilus biguttatus under the bark of affected trees are often reported. AOD is characterized by oak decline, after which a large proportion of the oaks die, but some survive. In Latvia, oaks with AOD symptoms were first observed in 2017, and the presence of Gibbsiella quercinecans and Brenneria goodwinii in the bark exudate was confirmed. A country-wide survey was initiated to assess the prevalence of oaks with AOD symptoms. In addition, experimental plots were established to monitor the progression of AOD in infected sites. A total of 1,329 forest stands were surveyed; 111 exudate samples were collected and 36 samples were positive for one of both B. goodwinii and G. quercinecans. Larval galleries or other signs of the beetle Agrllus biguttatus were not found in association with AOD symptoms. Four trial plots were established and routinely monitored over a four-year period for AOD symptoms, presence of G. quercinecans and B. goodwinii, and an assessment of fungal species was done. In the trial plots, AOD symptoms peaked in 2019. Presence of the bacteria was not detected in all exudate samples collected regularly over summer from the trial plots. The presence of the bacteria was confirmed only in a few soil samples collected along a transect in one trial plot. One or both bacteria were identified in a few soil and wood samples collected from asymptomatic oak stands. Assessment of fungal species in both symptomatic and healthy trees did not identify significant differences in species composition, soil pH, fine root vitality, and mycorrhization. Environmental factor analysis indicated that precipitation in the previous autumn is related to a higher detection possibility of G. quercinecans and B. goodwinii in exudate samples collected in the following year. Continued monitoring for AOD symptoms, focussing on mature oak trees is required to identify future potential AOD outbreaks in Latvia. Keywords: Quercus robur; AOD; monitoring; qPCR; phytopathology; environmental factors

The Role of Bacteria in Acute Oak Decline in South-West Poland.

The process of multifactorial oak disease has been of interest to scientists from all over the world for many years. Recently, a new phenomenon has been added to the model related to oak decline, acute oak dieback, which causes oak decline and was first described in the UK. This study presents research on this phenomenon in the area of the largest oak stand complex in Poland, the so-called Krotoszyn Plateau. This work was carried out in two stages. In the first stage, 54 trees were tested for the presence of bacteria using molecular biology (real-time PCR). Subsequently, a tissue fragment was taken for inoculation from the trees in which the presence of B. goodwinii and G. quercinecans bacteria was confirmed. The isolates obtained were used to test Koch's postulates and for biochemical analyses for Polish strains. In addition, the results obtained were also compared with the presence of A. biguttatus, which is considered a bacterial vector, which, in turn, confirmed that the bacteria responsible for the AOD phenomenon can also be present in trees not inhabited by this insect. The results obtained confirmed the presence of bacteria and their potential to cause necrosis in oaks, which fits into the model of the spiral disease that has been causing mass mortality of oaks in this naturally and economically valuable area since the 1980s.

Alien invasive pathogens and pests in the changing environment: Focus on North Europe

On 12–13 September 2023, a panel of forest pathologists and entomologists gathered in Visby, Gotland Island, Baltic Sea, Sweden. The participants, a total of 20, represented all five Nordic Countries, three Baltic States, and Ukraine, and also joined by the local stakeholders representing the Swedish Forestry Agency and Gotland Administration. The purpose was to conduct a scientific workshop focusing on invasive tree pests and diseases emerging in each respective country, as well as to participate in an excursion to damaged woodland sites of Gotland. The Nordic Forest Research (SNS) financially supported the event (https://nordicforestresearch.org/n2023-01/). Keywords: Corinectria / Neonectria cankers; Hymenoscyphus fraxineus; Emerald Ash Borer; Diplodia sapinea; Acute Oak Decline; Polygraphus proximus; emerging birch pests; Bronze Birch Borer; Thekopsora areolata; seedborn conifer fungi

Acute and Chronic Oak Decline in urban and forest ecosystems in Southern Italy

Abstract Since recently, a decline of holm oak (Quercus ilex L.) is observed in Salento (South Italy), this caused concern regarding the protection of native biodiversity and local forests. Symptomatic trees show browning of leaves, thinning of canopy, and loss of branches. The aim of this study was to understand the biotic factors involved in the observed decline. During the monitoring activity, the use of phenotypic descriptors highlighted the presence of two types of decline with distinct symptoms among oaks in rural and urban areas, which could be classified as Acute Oak Decline (AOD) and Chronic Oak Decline (COD), respectively. Following this, diagnostic analyses were carried out to assess the presence of various holm oak pathogens on twigs, trunk, and soil. These analyses revealed the presence of several Botryosphaeriaceae oak pathogens, present ubiquitously between the two environmental contexts, with Diplodia seriata being overall the most prevalent. Contrarily, bacteria associated with AOD were only present in the rural areas and included: Brenneria goodwinii, Gibbsiella quercinecans, and Rahnella victoriana. As far as known to the authors, this is the first time these pathogens have been found in the Mediterranean coastal regions. Lastly, soil analyses performed to detect the presence of Phytophthora cinnamomi were negative. Our results highlight the presence of several pathogens, which indicates that oak decline is a multifactorial phenomenon for which the predisposing, initial, and contributing factors are not yet known particularly for the recently described AOD and COD. Finally, the identification of AOD-related bacteria in Salento is a cause of concern for the need of urgent management actions aimed to contain their spread and to preserve the forest heritage of the region.

Bacteria Associated with Acute Oak Decline: Where Did They Come From? We Know Where They Go.

Acute oak decline is a high-impact disease causing necrotic lesions on the trunk, crown thinning and the eventual death of oak. Four bacterial species are associated with the lesions-Brenneria goodwinii, Gibbsiella quercinecans, Rahnella victoriana and Lonsdalea Britannica-although an epi-/endophytic lifestyle has also been suggested for these bacteria. However, little is known about their environmental reservoirs or their pathway to endophytic colonisation. This work aimed to investigate the ability of the four AOD-associated bacterial species to survive for prolonged periods within rhizosphere soil, leaves and acorns in vitro, and to design an appropriate method for their recovery. This method was trialled on field samples related to healthy and symptomatic oaks. The in vitro study showed that the majority of these species could survive for at least six weeks within each sample type. Results from the field samples demonstrated that R. victoriana and G. quercinecans appear environmentally widespread, indicating multiple routes of endophytic colonisation might be plausible. B. goodwinii and L. britannica were only identified from acorns from healthy and symptomatic trees, indicating they may be inherited members of the endophytic seed microbiome and, despite their ability to survive outside of the host, their environmental occurrence is limited. Future research should focus on preventative measures targeting the abiotic factors of AOD, how endophytic bacteria shift to a pathogenic cycle and the identification of resilient seed stock that is less susceptible to AOD.

Bioclimatic variables and their impact on the potential distribution of Brenneria goodwinii in Europe

AbstractBrenneria goodwinii is a Gram‐negative bacterium associated with the phenomenon of Acute Oak Decline (AOD), which has played a very important role in the decline of oak populations in Europe in recent years. In this paper, the Maxent model was developed to detect the trend in the distribution of B. goodwinii in Europe. Generated from confirmed location data and bioclimatic variables, the Maxent model achieved high predictive accuracy as measured by parameters such as AUC and AUCdiff. Nineteen bioclimatic variables available on the WorldClim portal for the years 1970–2000 were used to create the model. The generated model allows to determine the most useful bioclimatic variables to assess the maximum entropy of the habitat in terms of the occurrence of B. goodwinii. In addition, the model identified areas of Europe where the probabilities of fit for bacteria are >.7. These areas include Great Britain, France, Belgium, the Netherlands, Germany, Denmark, Spain, Portugal and Italy.

Description of Dryocola gen. nov. and two novel species, Dryocola boscaweniae sp. nov. and Dryocola clanedunensis sp. nov. isolated from the rhizosphere of native British oaks

While investigating the role of the rhizosphere in the development of Acute Oak Decline, bacterial strains belonging to the family Enterobacteriaceae were isolated from rhizosphere soil following enrichment for the Enterobacterales. Partial sequencing of several housekeeping genes showed that these strains could not be assigned to an existing genus. Overall, 16 strains were investigated using a polyphasic approach to determine their taxonomic status. This involved phenotypic testing and fatty acid analysis paired with phylogenetic analyses of 16S rRNA and housekeeping gene sequences, as well as phylogenomic analysis of whole genome sequences. Phylogenomic and phylogenetic analyses consistently demonstrated that the 16 isolates could be separated into two distinct clusters in a monophyletic clade situated between the genera Cedecea and Buttiauxella. The two clusters could be genotypically and phenotypically differentiated from each other and from their closest neighbours. As such we propose the description of Dryocola boscaweniae gen. nov. sp. nov. (type strain H6W4T = CCUG 76177T = LMG 32610T) and Dryocola clanedunesis sp. nov. (type strain H11S18T = CCUG 76181T = LMG 32611T).

Microbial Community Structure among Honey Samples of Different Pollen Origin.

Honey's antibacterial activity has been recently linked to the inhibitory effects of honey microbiota against a range of foodborne and human pathogens. In the current study, the microbial community structure of honey samples exerting pronounced antimicrobial activity was examined. The honey samples were obtained from different geographical locations in Greece and had diverse pollen origin (fir, cotton, fir-oak, and Arbutus unedo honeys). Identification of honey microbiota was performed by high-throughput amplicon sequencing analysis, detecting 335 distinct taxa in the analyzed samples. Regarding ecological indices, the fir and cotton honeys possessed greater diversity than the fir-oak and Arbutus unedo ones. Lactobacillus kunkeei (basionym of Apilactobacillus kun-keei) was the predominant taxon in the fir honey examined. Lactobacillus spp. appeared to be favored in honey from fir-originated pollen and nectar since lactobacilli were more pronounced in fir compared to fir-oak honey. Pseudomonas, Streptococcus, Lysobacter and Meiothermus were the predominant taxa in cotton honey, whereas Lonsdalea, the causing agent of acute oak decline, and Zymobacter, an osmotolerant facultative anaerobic fermenter, were the dominant taxa in fir-oak honey. Moreover, methylotrophic bacteria represented 1.3-3% of the total relative abundance, independently of the geographical and pollen origin, indicating that methylotrophy plays an important role in honeybee ecology and functionality. A total of 14 taxa were identified in all examined honey samples, including bacilli/anoxybacilli, paracocci, lysobacters, pseudomonads, and sphingomonads. It is concluded that microbial constituents of the honey samples examined were native gut microbiota of melliferous bees and microbiota of their flowering plants, including both beneficial bacteria, such as potential probiotic strains, and animal and plant pathogens, e.g., Staphylococcus spp. and Lonsdalea spp. Further experimentation will elucidate aspects of potential application of microbial bioindicators in identifying the authenticity of honey and honeybee-derived products.

Description of a novel species of Leclercia, Leclercia tamurae sp. nov. and proposal of a novel genus Silvania gen. nov. containing two novel species Silvania hatchlandensis sp. nov. and Silvania confinis sp. nov. isolated from the rhizosphere of oak

BackgroundAcute Oak Decline (AOD) is a decline disease first reported on native oaks in the UK, but in recent years reports from further afield such as Europe and the Middle East, indicate that the distribution and host range is increasing at an alarming rate. The stem weeping symptoms of the disease partially develop due to polymicrobial-host interaction, caused by several members of the order Enterobacterales. While investigating the rhizosphere soil of AOD-unaffected trees, termed ‘healthy’ trees, and diseased oaks suffering from Acute Oak Decline (AOD), an enrichment method designed for enhanced recovery of Enterobacterales led to the recovery of several isolates that could not be classified as any existing species. These isolates showed a close relationship to the genus Leclercia, of which both species are of clinical importance, but the type species Leclercia adecarboxylata also displays plant growth-promoting properties in the rhizosphere.ResultsPartial sequencing of four housekeeping genes revealed similarity to the genus Leclercia with varying degrees of relatedness. As such a complete polyphasic approach was used to determine the true taxonomic position of these isolates. This involved whole genome sequencing, phylogenomic analysis, phylogenetic analysis of both the 16S rRNA and four housekeeping gene sequences, combined with phenotypic testing and fatty acid analysis. Both the phylogenomic and phylogenetic analyses separated the isolates into four clusters, two of which were contained in the Leclercia clade. The remaining two clusters formed a separate lineage far removed from any currently defined species. Further investigation into the role of the isolates as plant growth-promoting bacteria as well as plant pathogens was investigated computationally, revealing a number of plant growth-promoting traits as well as virulence genes related to motility, adhesion and immune modulation.ConclusionBased on the genotypic and phenotypic data presented here, these isolates could be differentiated from each other and their closest neighbours. As such we propose the description of Leclercia tamurae sp. nov. (type strain H6S3T = LMG 32609T = CCUG 76176T), Silvania gen. nov., Silvania hatchlandensis sp. nov. (type strain H19S6T = LMG 32608T = CCUG 76185T) and Silvania confinis sp. nov. (type strain H4N4T = LMG 32607T = CCUG 76175T). Due to their interesting protein annotations and alignments, these species warrant further investigation for their role in relation to plant health.

Worldwide review of bacterial diseases of oaks (Quercus sp.) and their potential threat to trees in Central Europe

Abstract The phenomenon of hhh Europe has been observed for over 100 years. In this time, many attempts have been made to describe this phenomenon considering biotic, abiotic and anthropogenic factors. Recently, an increasing intensity of bacterial tree diseases has been observed both in Europe and around the world. Moreover, climate change is contributing to an increase in the range of pathogens. The aim of this publication was to highlight the most important bacterial diseases occurring on oaks around the world, and to discuss the potential threat to native oaks occurring in Central Europe: English oak (Quercus robur L.) and sessile oak (Quercus petraea (Matt.) Liebl.). The main focus was on three diseases caused by different bacteria: bacterial leaf streak (caused by Xylella fastidiosa), acute oak decline (caused by Gibbsiella quercinecans, Rahnella victoriana and Brenneria goodwinii) and drippy nut disease (caused by Brenneria quercina—formerly Erwinia quercina). At present, these are the only known bacterial diseases that cause damage to oak stands. Information on each of the above-mentioned diseases is given in the review, ranging from their origin, importance, list of host plants and their potential threat to native oaks of Central Europe.

Acute oak decline (AOD) new complex disese on holm oak (Quercus ilex L.) and possibilities of spread on other oak species in Croatia

U radu se prikazuje pregled dosadašnjih saznanja o Akutnom odumiranju hrastova (AOH), u svijetu opisanom kao AOD (Acute oak decline). Ova polimikrobna bolest je nedavno otkrivena u Hrvatskoj (2021. godine) na poluotoku Pelegrin (otok Hvar), gdje se na stablima hrasta crnike zadnjih nekoliko godina javljaju tipični simptomi: sušenje vrhova krošnje koje prate uzdužne raspukline kore, gdje istodobno ispod kore dolazi do odumiranja tkiva u obliku crnih nekroza. U kasnijoj fazi javljaju se i tekline te se vide izlazne rupe kukaca, a stablo nakon 3-4 godine odumire. Bolest se širi sa stabla na stablo, a krajnja posljedica je masovno sušenje. Uzročnici odumiranja tkiva pod korom su patogene bakterije Brenneria godwinii, Gibbsiella quercinecans i Lonsdalea britannica, a njihovi mogući prijenosnici su krasnici Agrilus sulcicolis i A. olivicolor. AOH je do sada opisana u Ujedinjenom kraljevstvu, Latviji, Španjolskoj, Iranu i Švicarskoj. Važnost prvog nalaza AOH u Hrvatskoj je što hrast crnika kao autohtona vrsta ima posebno značenjej za Mediteranske šume, a k tome su po prvi puta nađene i vrste krasnika koje do sada nisu potvrđene kao vektori AOH. Posebno se naglašava rizik prijelaza AOH na kontinentalne šume hrasta lužnjaka i kitnjaka, jer za razliku od svih dosadašnjih nalaza AOH u svijetu, lužnjakove i kitnjakove šume u Hrvatskoj su jedine koje su već godinama izložene napadima hrastove mrežaste stjenice (Corythucha arcuata). Moguća kombinacija hrastove mrežaste stjenice i AOH mogla bi biti iznimno opasna. Stoga se naglašava promptna primjena mjera zaštite, posebice preventivnih te važnost znanstvenih istraživanja.

Description of three novel species of Scandinavium: Scandinavium hiltneri sp. nov., Scandinavium manionii sp. nov. and Scandinavium tedordense sp. nov., isolated from the oak rhizosphere and bleeding cankers of broadleaf hosts.

While investigating the bacterial populations of environmental samples taken from a mix of healthy and Acute Oak Decline afflicted Quercus robur (pedunculate or English oak) rhizosphere soil samples and swabs of bleeding lesions on Tilia spp. (lime) and Quercus rubra (red oak) trees, several strains belonging to the order Enterobacterales were isolated using selective media and enrichment broth. Seven strains from the Q. robur rhizosphere, three strains from Tilia spp. and one from Q. rubra were investigated, with their taxonomic status determined via a polyphasic taxonomic approach. Initially stains were identified as potential members of the recently described genus Scandinavium, based on the partial sequencing of three housekeeping genes. Further analysis of phenotypic traits, including fatty acid profiles, coupled with 16S rRNA gene and phylogenomic analysis of whole genome sequences were applied to a subset of the strains. Phylogenetic and phylogenomic analysis repeatedly placed the isolates in a monophyletic clade within Scandinavium, with four distinct clusters observed, one of which corresponded to Scandinavium goeteborgense, the type species of the genus. The remaining three clusters could be phenotypically and genotypically differentiated from each other and S. goeteborgense. As such, we describe three novel species of the genus, for which we propose the names Scandinavium hiltneri sp. nov. (type strain H11S7T = LMG 32612T = CCUG 76179T), Scandinavium manionii sp. nov. (type strain H17S15T = LMG 32613T = CCUG 76183T) and Scandinavium tedordense sp. nov. (type strain TWS1aT = LMG 32614T = CCUG 76188T). Additionally, the descriptions of the genus Scandinavium and the type species, S. goeteborgense, are emended.

11- Acute oak decline disease

11- Acute oak decline disease

First report of Brenneria goodwinii causing acute oak decline on Quercus suber in Portugal

First report of Brenneria goodwinii causing acute oak decline on Quercus suber in Portugal

Brenneria goodwinii growth in vitro is improved by competitive interactions with other bacterial species associated with Acute Oak Decline.

Brenneria goodwinii, Rahnella victoriana and Gibbsiella quercinecans are three bacterial species frequently isolated together from oak displaying symptoms of Acute Oak Decline (AOD), which include weeping patches on trunks. All three bacterial species play a role in lesion formation in the current episode of AOD in Britain, although B. goodwinii is the most dominant. The ongoing research into stem lesion formation characteristic of this polybacterial syndrome has been focussed primarily on the pathogenicity, identification and taxonomy of these bacteria. As all three species were newly classified within the past ten years, there are many unanswered questions regarding their ecology and interactions with each other. To determine the effect of bacterial interactions on fitness in vitro, we examined pairwise (diculture) and multispecies (triculture) interactions between B. goodwinii, R. victoriana and G. quercinecans in oak leaf media microcosms. Additionally, the effect of co-culturing on the evolution of these species was determined and the evolved B. goodwinii strains were examined further by whole genome sequencing. Our results indicate that B. goodwinii thrived in monoculture with significantly higher viable cell counts than the other two species. Additionally, B. goodwinii performed well in pairwise culture with mutually competitive interactions observed between B. goodwinii and R. victoriana, and between B. goodwinii and G. quercinecans. In the multispecies triculture, B. goodwinii and R. victoriana appeared to exhibit co-ordinated behaviour to outcompete G. quercinecans. After four weeks B. goodwinii grown in co-culture with the other two species developed greater evolved fitness than the strain grown in monoculture as reflected by the increased viable cell counts. The competitive interactions taking place between the threes species indicated evolving improved fitness of B. goodwinii in vitro, that gave it a growth advantage over both R. victoriana and G. quercinecans which showed no significant changes in fitness. Overall, B. goodwinii gains greater benefit in terms of fitness from in vitro competitive interaction with the other two species.

Evidence for the Widespread Occurrence of Bacteria Implicated in Acute Oak Decline from Incidental Genetic Sampling

Acute Oak Decline (AOD) is complex syndrome affecting Britain’s keystone native oak species, (Quercus robur L. and Q. petraea L. (Matt.) Liebl.), in some cases causing mortality within five years of symptom development. The most distinguishable symptom is weeping stem lesions, from which four species of bacteria have been isolated: Brenneria goodwinii, Gibbsiella quercinecans, Lonsdalea britannica and Rahnella victoriana. We do not yet know where else these bacteria exist, and little is known about the relationship of the wider oak leaf microbiome (phyllosphere) to acute oak decline. Here we investigate whether incidental evidence from a large oak genome re-sequencing dataset could be used to detect these bacteria in oak foliage, and whether bacterial incidence co-varied with AOD status or location. Oak leaves and buds were sampled from 421 trees at five sites in England. Whole genomic DNA from these samples was shot-gun sequenced with short reads. Non-oak reads were extracted from these data and queried to microbial databases. Reads uniquely matching AOD-associated bacterial genomes were found to be present on trees from all five sites and included trees with active lesions, trees with historic lesions and trees without AOD symptoms. The abundance of the AOD-associated bacteria did not differ between tree health categories but did differ among sites. We conclude that the AOD-associated bacteria may be members of the normal oak microbiome, whose presence on a tree is not sufficient to cause AOD symptoms.

The distribution of bacteria Gibbsiella quercinecans and Brenneria goodwinii in oak (Quercus robur L.) stands in Latvia

Acute Oak Decline (AOD) is a complex plant disease affecting species of native oaks, for example, Quercus robur, in Latvia. Typical AOD symptoms are bark cracks with dark exudate. In other European region countries, like the United Kingdom, AOD is associated with bark insects, for example, Agrilus biguttatus. From the results of the forest survey, it can be concluded that in oak forest stands located in Latvia, there is practically no damage by the bark insect A. biguttatus, which may indicate the existence of another AOD spreading vector. In 2019, from one oak, which was positive for AOD in the spring, repeated stem bleed samples were taken in the autumn period, the laboratory analysis results of the repeated samplings were negative. These findings suggest that the activity of bacteria Brenneria goodwinii and Gibbsiella quercinecans are influenced by climatic conditions.

Genomic structure and diversity of oak populations in British parklands

Societal Impact StatementThe largest populations of veteran oak trees in Europe are found in British parklands: managed wood pastures up to 1000 years old. Here, we present genomic evidence that parkland oak populations harbour considerable diversity and grew from local seed sources. We found some evidence for natural regeneration of offspring and for hybridization between pedunculate and sessile oak. We detected signatures of past gene flow between these two species and few regions of high differentiation within their genomes. Future expansion of this dataset may allow us to test for a genomic basis of acute oak decline, a syndrome of particular concern in parkland environments.Summary The two predominant oak species in Europe, Quercus robur (English or pedunculate oak) and Quercus petraea (sessile oak), have a long history of human intervention. In Britain, a common management regime is parklands, often surrounding country houses. Little is known about how seeds were sourced for parkland oak populations nor the genetic diversity that they contain. We sequenced the whole genomes of 386 trees from four British parkland sites to characterize the nuclear and chloroplast genetic structure and diversity of oak parkland populations. We assembled the chloroplast genomes and matched these to restriction enzyme fragment chloroplast haplotypes found in previous studies of ancient woodlands. We found over two million high‐quality nuclear single‐nucleotide polymorphisms (SNPs), allowing us to identify 360 Q. robur, 10 Q. petraea and 16 hybrid individuals with confidence. We identified 81 coding regions exhibiting strong differentiation between the two species. We found evidence for selective sweeps in Q. robur near some regions containing genes with putative involvement in stress tolerance. We detected a few very close relatives within some sites, suggesting natural regeneration or local seed planting. There was little differentiation among the Q. robur populations at the four sites. Chloroplast genomes found in each parkland tended to be similar to those of local ancient woodlands, suggesting that they were derived from local seed sources.

First report of Brenneria goodwinii and Gibbsiella quercinecans bacteria, detected on weaken oak trees in Poland

The decline of oak stands is a phenomenon that has been observed since the beginning of the 20th century in many European countries. It can be caused both with abiotic factors such as drought and fluctuations in groundwater levels, as well as biotic factors such as infestations by insects, fungi and bacteria. Acute Oak Decline (AOD) is an dangerous disease of oak trees which was first observed in the XX century. From the moment the first symptoms were noticed, the disease is able to kill trees in up to 6 years. Two species of bacteria, Brebberia goodwinii and Gibsiella quercinecand, are considered as one of the infectious agents of AOD. The decline of Quercs robur was reported from a weakened stand from the Chojnów Forest District. Symptomatic exudates were sampled and subjected to laboratory analysis. Using the Real time PCR, bacteria Brenneria goodwinii and Gibsiella quercinecans were confirmed in two out of seven collected field samples. This report is the first information on the observation of these bacteria in weakened stands with the participation of Quercus robur in Poland. Keywords: Quercus robur, bacteria, Brenneria goodwinii, Gibsiella quercinecans, real time PCR, Acute Oak Decline