Oak Wilt Disease Research Articles

Japanese Oak Wilt Disease decreased survival probability and mean lifetime of tree populations in a secondary natural forest

ABSTRACT The purpose of this study was to assess the effects of Japanese Oak Wilt Disease on mortality in a tree population. The study site was the permanent plot of 0.26 ha established in the secondary forest dominated by Abies firma, Tsuga sieboldii and Quercus serrata at the University of Tokyo Chiba Forest in the southeastern part of the Boso peninsula, Japan. We set the two observation periods of 1999–2008 and 2009–2021, and Japanese Oak Wilt Disease invaded the study site in the middle of the second period. We collected tree age data for both alive and dead trees in the two periods based on semi-nondestructive drilling measurements for trees using a RESISTOGRAPH. Survival analyses were conducted on the second-period data, and the demographic metrics such as mortality ratios and mean lifetimes were compared between the two periods. The results showed that: the mortality ratio of the tree population at old ages, where oaks (Quercus serrata) concentrated in their age distribution, significantly increased; the effect of the oak group was significant on mortality in the tree population; the hazard for the oak group was 24 times the hazard for the other tree species group; the survival curve reflected the mass mortality in oaks at old ages, which led to the decrease of mean lifetime less than half. Consequently, it was implied that the effects of Japanese Oak Wilt Disease impacted the demographic metrics of oak trees.

Antifungal Activity of Culture Filtrate from Endophytic Fungus Nectria balsamea E282 and Its Fractions against Dryadomyces quercus-mongolicae

A key role that fungal endophytes play in interacting with their host plant can be defined by the fact that they promote the growth of plants and enhance the tolerance of the host against plant pathogens using bioactive compounds that they produce. Several studies utilizing endophytic fungi as a source of biological control against plant pathogens were conducted, and a representative example includes Aureobasidium protae from common wheat (Triticum aestivum), which inhibited the mycelial growth of Fusarium graminearum and Fusarium culmorum, causal agents of Fusarium head blight disease. Our previous study indicated that three endophytic fungal isolates, E089 (Daldinia childiae), E282 (Nectria balsamea), and E409 (Colletotrichum acutatum), showed antifungal activities against D. quercus-mongolicae, an ascomycetous fungus that is reported to be associated with oak mortality in South Korea. The objectives of this study were to optimize and evaluate antifungal efficiency for these endophytic fungi against D. quercus-mongolicae, and this was achieved using culture filtrate retrieved from the three above-mentioned endophytes and fractions isolated from the culture filtrate. Of those, the culture filtrate from E282 showed higher mycelial growth and sporulation inhibitions on PDA medium where D. quercus-mongolicae was grown. In addition, three fractions, including hexane, CHCl3, Et2O, and H2O, were tested for antifungal activities against D. quercus-mongolicae. The results revealed that the Et2O fraction showed higher mycelial growth and sporulation inhibition rates. Taking these results together, the endophytic fungus, N. balsamea, which exhibited high antifungal efficiency, can be effectively used as a biocontrol agent for the management of oak wilt disease in the country.

Biosurveillance of oak wilt disease in Canadian areas at risk

Biosurveillance of invasive species is critical for protecting native ecosystems and limiting economic losses. Early detection of pathogens through qPCR methods has recently shown great promise and can potentially slow the spread of devastating diseases. For instance, oak wilt, a disease caused by the fungus Bretziella fagacearum, can kill mature trees within weeks of infection. Originally contained in the USA, oak wilt has finally made its way into Canada, where it was recently observed for the first time in June 2023. This study has laid the foundations for a biosurveillance monitoring programme of B. fagacearum in Eastern Canada. From 2019–2021, insect vectors were baited and captured in Lindgren traps in various locations of interest, namely sawmills importing oak logs from the USA, forested areas containing mature oak trees and strategic sites along the border between the two countries. Insect vectors and collection fluids were analysed with our qPCR detection test for the presence of B. fagacearum. As a positive control to validate this method, we included traps in a known centre of oak wilt infection in Michigan (USA). Our analysis showed only one positive site at the border between Ontario (CA) and the USA, even though oak wilt has never been observed there. This result confirms that DNA from B. fagacearum can be detected with this method even before the appearance of symptomatic trees, which could be crucial in the current containment efforts in Ontario (CA).

Mapping oak wilt disease from space using land surface phenology

Protecting the future of forests relies on our ability to observe changes in forest health. Thus, developing tools for sensing diseases in a timely fashion is critical for managing threats at broad scales. Oak wilt —a disease caused by a pathogenic fungus (Bretziella fagacearum)— is threatening oaks, killing thousands yearly while negatively impacting the ecosystem services they provide. Here we propose a novel workflow for mapping oak wilt by targeting temporal disease progression through symptoms using land surface phenology (LSP) from spaceborne observations. By doing so, we hypothesize that phenological changes in pigments and photosynthetic activity of trees affected by oak wilt can be tracked using LSP metrics derived from the Chlorophyll/Carotenoid Index (CCI). We used dense time-series observations from Sentinel-2 to create Analysis Ready Data across Minnesota and Wisconsin and to derive three LSP metrics: the value of CCI at the start and end of the growing season, and the coefficient of variation of the CCI during the growing season. We integrate high-resolution airborne imagery in multiple locations to select pixels (n = 3872) from the most common oak tree health conditions: healthy, symptomatic for oak wilt, and dead. These pixels were used to train an iterative Partial Least Square Discriminant (PLSD) model and derive the probability of an oak tree (i.e., pixel) in one of these conditions and the associated uncertainty. We assessed these models spatially and temporally on testing datasets revealing that it is feasible to discriminate among the three health conditions with overall accuracy between 80 and 82%. Within conditions, our models suggest that spatial variations among three CCI-derived LSP metrics can identify healthy (Area Under the Curve (AUC) = 0.98), symptomatic (AUC = 0.89), and dead (AUC = 0.94) oak trees with low false positive rates. The model performance was robust across different years as well. The predictive maps were used to guide local stakeholders to locate disease hotspots for ground verification and subsequent decision-making for treatment. Our results highlight the capabilities of LSP metrics from dense spaceborne observations to map diseases and to monitor large-scale change in biodiversity.

Dynamics of litterfall production in a forest damaged by oak wilt disease: a case study in a warm-temperate secondary forest

ABSTRACT Quantification of litterfall production is crucial for evaluating net primary productivity and nutrient cycling in forest ecosystems. High mortality among trees in the family Fagaceae due to Japanese oak wilt disease (JOW) might affect litterfall production in secondary forests; however, few studies have quantified these effects. We investigated litterfall production and forest structure in warm-temperate secondary forests in the Kaisho Forest over 6 and 12 years, respectively, and compared the dynamics among different phases of a JOW outbreak to assess the impacts of JOW on litterfall production. We found that total annual litterfall and leaf fall showed little change in peak to post-JOW periods and that changes in basal area were unrelated to total litterfall and leaf fall. The observed fluctuation in BA in the Kaisho Forest may not have been large enough to clearly reveal the effect of JOW during these periods. Canopy gaps formed by JOW may enhance the recruitment and growth rates of sub-canopy and understory trees. Our results may only be applicable to warm secondary forests where evergreen trees are replacing deciduous trees. Additional information on litterfall production in JOW-disturbed secondary forests is needed.

Independent Evolution Has Led to Distinct Genomic Signatures in Dutch Elm Disease-Causing Fungi and Other Vascular Wilts-Causing Fungal Pathogens.

Vascular wilts are important diseases caused by plant pathogenic fungi that result in the rapid death of their plant hosts. This is due to a systemic defense mechanism whereby the plant induces the compartmentalization of the infected vascular system in order to reduce the propagation of the fungus. The ascomycete class Sordariomycetes contains several species that cause vascular wilts in diverse plant hosts, and they can be classified into four taxonomic orders. The genetic mechanisms of pathogenesis have already been investigated in Fusarium and Verticillium species, but they have not yet been compared with other well-known wilt-causing species, especially fungi causing oak wilt or Dutch elm disease (DED). Here we analyzed 20 whole genome assemblies of wilt-causing fungi together with 56 other species using phylogenetic approaches to trace expansions and contractions of orthologous gene families and gene classes related to pathogenicity. We found that the wilt-causing pathogens evolved seven times, experiencing the largest fold changes in different classes of genes almost every time. However, some similarities exist across groups of wilt pathogens, particularly in Microascales and Ophiostomatales, and these include the common gains and losses of genes that make up secondary metabolite clusters (SMC). DED pathogens do not experience large-scale gene expansions, with most of the gene classes, except for some SMC families, reducing in number. We also found that gene family expansions in the most recent common ancestors of wilt pathogen groups are enriched for carbohydrate metabolic processes. Our study shows that wilt-causing species evolve primarily through distinct changes in their repertoires of pathogenicity-related genes and that there is the potential importance of carbohydrate metabolism genes for regulating osmosis in those pathogens that penetrate the plant vascular system.

Patterns of community composition and diversity in latent fungi of living Quercus serrata trunks across a range of oak wilt prevalence and climate variables in Japan

Given that forest dieback due to emerging pests is increasing under global warming, understanding the relationships between pests, climate, and forest biodiversity is an urgent priority. In Japan, mass attacks of an ambrosia beetle, vectoring a pathogenic fungus, cause oak wilt outbreaks in recent decades. Here, the associations of oak wilt and climate with wood-inhabiting fungal communities in apparently healthy Quercus serrata trunks were investigated using DNA metabarcoding in seven sites along a climatic gradient in Japan. Amplicon sequencing of the fungal internal transcribed spacer 1 region generated 1,339,958 sequence reads containing 879 fungal operational taxonomic units (OTUs) in 234 wood samples. OTU compositions were significantly different between sites with and without oak wilt. OTU richness increased with temperature and precipitation at sites where oak wilt was present, but this relationship was not observed at sites without oak wilt, possibly due to interaction between oak wilt and climate. • Oak wilt disease is correlated with fungal communities in living oak trees. • OTU richness increased with temperature and precipitation at sites with oak wilt. • OTU richness was not correlated with macroclimate at sites without oak wilt. • Oak wilt was correlated with absence of some white-rot decomposer fungi. • Precipitation had a negative correlation with the species richness of brown-rot fungi.

Canopy spectral reflectance detects oak wilt at the landscape scale using phylogenetic discrimination

The oak wilt disease caused by the invasive fungal pathogen Bretziella fagacearum is one of the greatest threats to oak-dominated forests across the Eastern United States. Accurate detection and monitoring over large areas are necessary for management activities to effectively mitigate and prevent the spread of oak wilt. Canopy spectral reflectance contains both phylogenetic and physiological information across the visible near-infrared (VNIR) and short-wave infrared (SWIR) ranges that can be used to identify diseased red oaks. We develop partial least square discriminant analysis (PLS-DA) models using airborne hyperspectral reflectance to detect diseased canopies and assess the importance of VNIR, SWIR, phylogeny, and physiology for oak wilt detection. We achieve high accuracy through a three-step phylogenetic process in which we first distinguish oaks from other species (90% accuracy), then red oaks from white oaks (Quercus macrocarpa) (93% accuracy), and, lastly, infected from non-infected trees (80% accuracy). Including SWIR wavelengths increased model accuracy by ca. 20% relative to models based on VIS-NIR wavelengths alone; using a phylogenetic approach also increased model accuracy by ca. 20% over a single-step classification. SWIR wavelengths include spectral information important in differentiating red oaks from other species and in distinguishing diseased red oaks from healthy red oaks. We determined the most important wavelengths to identify oak species, red oaks, and diseased red oaks. We also demonstrated that several multispectral indices associated with physiological decline can detect differences between healthy and diseased trees. The wavelengths in these indices also tended to be among the most important wavelengths for disease detection within PLS-DA models, indicating a convergence of the methods. Indices were most significant for detecting oak wilt during late August, especially those associated with canopy photosynthetic activity and water status. Our study suggests that coupling phylogenetics, physiology, and canopy spectral reflectance provides an interdisciplinary and comprehensive approach that enables detection of forest diseases at large scales. These results have potential for direct application by forest managers for detection to initiate actions to mitigate the disease and prevent pathogen spread.

Transpiration Response of Neighboring Trees to the Wilting of Oak Individuals Prone to Japanese Oak Wilt Disease

Transpiration Response of Neighboring Trees to the Wilting of Oak Individuals Prone to Japanese Oak Wilt Disease

Fungal Community Analyses of Endophytic Fungi from Two Oak Species, Quercus mongolica and Quercus serrata, in Korea

Fungal endophytes have been recorded in various plant species with a richness of diversity, and their presence plays an essential role in host plant protection against biotic and abiotic stresses. This study applied the Illumina MiSeq sequencing platform based on the amplification of fungal ribosomal ITS2 region to analyze fungal endophytic communities of two oak species (Quercus mongolica and Q. serrata) with different oak wilt disease susceptibilities in Korea. The results showed a total of 230,768 sequencing reads were obtained and clustered at a 97% similarity threshold into 709 operational taxonomic units (OTUs). The OTUs of Q. serrata were higher than that of Q. mongolica with the number of 617 OTUs and 512 OTUs, respectively. Shannon index also showed that Q. serrata had a significantly higher level of fungal diversity than Q. mongolica. Total of OTUs were assigned into 5 fungal phyla, 17 classes, 60 orders, 133 families, 195 genera, and 280 species. Ascomycota was the dominant phylum with 75.11% relative abundance, followed by Basidiomycota with 5.28%. Leptosillia, Aureobasidium and Acanthostigma were the most abundant genera detected in Q. serrata with the average relative abundance of 2.85, 2.76, and 2.19%, respectively. On the other hand, Peltaster, Cladosporium and Monochaetia were the most common genera detected in Q. mongolica with the average relative abundance of 4.83, 3.03, and 2.87%, respectively. Our results indicated that fungal endophytic communities were significantly different between two oak species and these differences could influence responses of host trees to oak wilt disease caused by Raffaelea quercus-mongolicae.

Evaluation of Strength Performance of the Fumigation Treated Wood Affected by the Oak Wilt Disease

Fumigation treatment is mainly used on dead trees affected by the oak wilt disease to prevent the spread of damage. To verify the possibility of intensive use of the damaged Mongolian Oak wood treated by the fumigation treatment, we performed the compression and bending performance evaluation of the fumigation treated wood. The fumigation was done with Nemasect (Metam-sodium) for about 9 months. The dry longitudinal compressive strength of the fumigation treated oak wilt-diseased wood at the ambient temperature and humidity, and the compressive modulus of elasticity were measured to be 58.87MPa, and 5.66GPa, which were similar to the non-treated wood. The strength performance of mature wood of fumigation treated wood was 16% higher than that of juvenile wood. The compression fracture of the non-treated oak wood showed various shapes, however, most of the fumigation treated wood showed shear-type fracture shape. The bending strength of the fumigate treated wood was measured to be 157.43MPa, which was 8% higher than that of the non-treated wood, and the bending modulus of elasticity was measured to be 16.38GPa, which was 16% lower than that of the non-treated wood. However, it was confirmed that the coefficient of variation for the bending strength performance value of the fumigation treated wood was lower than that of the non-treated wood.

Comparison of Anatomical Characteristics for Wood Damaged by Oak Wilt and Sound Wood from Quercus mongolica

The aim of this study was to investigate the anatomical characteristics of Quercus mongolica infested by oak wilt disease. To analysis the anatomical characteristics of the wood specimens infested by the oak wilt, the anatomical structures of an infected wood, a dead wood, and sound wood were observed at 10-year-old intervals from 10 to 50 annual rings using both an optical and a scanning electron microscope. The fiber length was measured in units of 5 annual rings from the pith, and the diameter of the vessel element and the ratio of the vessel including the tyloses were measured for each 10 annual ring. In the cross section, on the infected and dead wood specimens, mycelium was also observed with the tyloses in the vessel. There was no signification difference between the wood specimens in the fiber length and the vessel diameter of the vessel element. The fiber length was not difference after 20-30 annual rings which is a part of juvenile wood. The average of the vessel ratio including tyloses in the infected wood was the highest. Especially, the ratio of tyloses was the highest 40-50 annual rings in the infected wood and the dead wood. Therefore, the large difference between the infested wood by oak wilt and the sound wood was the ratio of tyloses. This result can be used as a basic data to utilize the infested wood.

Screening of Endophytic Fungal Isolates Against Raffaelea quercus-mongolicae Causing Oak Wilt Disease in Korea

Oak wilt disease caused by Raffaelea quercus-mongolicae has emerged obviously in Korea. We selected antifungal isolates against R. quercus-mongolicae among 368 endophytic fungal isolates from different parts of oak and pine trees. The experiment was conducted in the primary and secondary screenings by dual culture test. The antifungal activity of the selected isolates was assessed in culture filtrate test based on the inhibition rates in mycelial growth, sporulation, and spore germination of oak wilt fungus. Five isolates, E089, E199, E282, E409 and E415, showed strong antifungal activity in culture filtrate test, and their antifungal activity decreased on the culture media supplemented with heated culture filtrate. Higher mycelial growth inhibitions on the unheated media were recorded in E409 (Colletotrichum acutatum), E089 (Daldinia childiae), E415 (Alternaria alternata) and E199 (Daldinia childiae) with the inhibition rates of 79.0%, 70.1%, 68.9% and 64.5%, respectively. These isolates also had the higher sporulation inhibitions on unheated media with the rates of 96.8%, 84.2%, 82.8% and 80.5%, respectively. The spore germination of the oak wilt fungus was completely inhibited by E282 (Nectria balsamea) on both unheated and heated media. These results showed that a higher number of potent antifungal isolates against oak wilt fungus was isolated from the petiole compared to the other parts. This study could contribute to the development of biological control approaches for the management of oak wilt disease caused by R. quercus-mongolicae.

New compounds from Japanese oak wilt disease-associated fungus Raffaelea quercivora

Two new compounds, a new lactone, quercilactone A (1), and (17R)-hydroxynafuredin (5), as well as five known compounds, scytalone (2), 3S,4R-hydoxy-scytalone (3), nafuredin (4), (+)-(3R,5R)-3-hydroxy-5-decanolide (6) and 3-ethyl-4-hydroxy-6-methyl-2H-pyran-2-one (7), were isolated from Raffaelea quercivora, a fungus that causes Japanese oak wilt disease. The structures of these compounds were determined by 1D and 2D NMR spectroscopic analyses. The absolute configuration at C-17 of 5 was determined to be R by the modified Mosher’s method. Compounds 1, 2, and 7 exhibited weak phytotoxic activity in lettuce seedlings at a concentration of 100 μg mL−1.

気象がナラ枯れ(ブナ科樹木萎凋病)に及ぼす影響に関する初歩的研究

気象がナラ枯れ(ブナ科樹木萎凋病)に及ぼす影響に関する初歩的研究

Spectral differentiation of oak wilt from foliar fungal disease and drought is correlated with physiological changes.

Hyperspectral reflectance tools have been used to detect multiple pathogens in agricultural settings and single sources of infection or broad declines in forest stands. However, differentiation of any one disease from other sources of tree stress is integral for stand and landscape-level applications in mixed species systems. We tested the ability of spectral models to differentiate oak wilt, a fatal disease in oaks caused by Bretziella fagacearum ``Bretz'', from among other mechanisms of decline. We subjected greenhouse-grown oak seedlings (Quercus ellipsoidalis ``E.J. Hill'' and Quercus macrocarpa ``Michx.'') to chronic drought or inoculation with the oak wilt fungus or bur oak blight fungus (Tubakia iowensis ``T.C. Harr. & D. McNew''). We measured leaf and canopy spectroscopic reflectance (400-2400nm) and instantaneous photosynthetic and stomatal conductance rates, then used partial least-squares discriminant analysis to predict treatment from hyperspectral data. We detected oak wilt before symptom appearance, and classified the disease with high accuracy in symptomatic leaves. Classification accuracy from spectra increased with declines in photosynthetic function in oak wilt-inoculated plants. Wavelengths diagnostic of oak wilt were only found in non-visible spectral regions and are associated with water status, non-structural carbohydrates and photosynthetic mechanisms. We show that hyperspectral models can differentiate oak wilt from other causes of tree decline and that detection is correlated with biological mechanisms of oak wilt infection and disease progression. We also show that within the canopy, symptom heterogeneity can reduce detection, but that symptomatic leaves and tree canopies are suitable for highly accurate diagnosis. Remote application of hyperspectral tools can be used for specific detection of disease across a multi-species forest stand exhibiting multiple stress symptoms.

Region-wide mass mortality of Japanese oak due to ambrosia beetle infestation: Mortality factors and change in oak abundance

Insect and pathogen disturbances can result in a decline in the abundance of host tree species, leading to changes in tree species composition at a regional scale. Quercus crispula and Q. serrata are dominant oak species in Japanese secondary forests, which are mostly composed of abandoned coppice. In recent decades, these two oak species have suffered mass mortality from Japanese oak wilt disease (JOW), which is caused by the ambrosia beetle Platypus quercivorus. This study analyzed factors affecting oak mortality during a JOW epidemic, and quantified the impact of the epidemic on forests at a regional scale in Toyama Prefecture, central Japan using data from 101 plots in the National Forest Inventory. Plot measurements before the epidemic (1999–2003) and re-measurements after the epidemic (2012–2014) were used for analysis. Before the epidemic, Q. crispula was the most dominant species in the natural forests and was distributed at a wider elevation range than Q. serrata (the third most dominant species). The mortality rate during the epidemic was 68% for Q. crispula and 21% for Q. serrata. The mortality of both species positively related with plot-level oak volume, suggesting that stand development after abandonment of coppice forests was an important factor in the epidemic. The mortality of Q. crispula related inversely with elevation and was especially low above 1000 m, probably because of the low reproductive success of P. quercivorus at high elevation, suggesting that global warming was a factor increasing the mortality from JOW. The total volume of Q. crispula in the study region decreased by 56% during the epidemic, while that of Q. serrata increased by 13%. After the epidemic, the dominance of Q. crispula in the natural forests decreased below that of Fagus crenata and Q. serrata. There were few regenerating Q. crispula and Q. serrata in the canopy gaps formed by dead oak because of their low numbers of saplings. Regenerating trees comprised various shade-tolerant canopy tree species and shrub species, and forests will change toward multispecies mixed, uneven-aged forests. This study comprehensively quantified forest change due to a JOW epidemic at a region-wide scale, and revealed that the epidemic was caused by multiple interactions among coppice abandonment, global warming, ambrosia beetles, and oak trees.

Early-stage vegetation recovery in forests damaged by oak wilt disease and deer browsing: effects of deer-proof fencing and clear-cutting

Oak wilt disease and deer browsing have depleted the canopy and forest floor of secondary Quercus serrata and Quercus variabilis forests in Japan. Small-scale clear-cuttings enhance sprouting, and are, therefore, recommended for restoration of the damaged forests. However, most damaged forests are composed of mature stands, and it is not clear whether they would sprout successfully when cut. Moreover, little is known about the regeneration of forests damaged by both oak wilt disease and deer browsing. To determine the appropriate treatment for restoration of damaged Q. serrata and Q. variabilis forests, we established a study site with three different treatments (10 × 30 m each) in Kyoto City: clear-cut and fenced, removed dead oak trees and fenced, and removed dead oak trees and unfenced. After 1-year treatment, the number of species and individual saplings tended to increase at the lower slope of each treatment site with dominance of Ilex pedunculosa. The largest species and individual numbers were observed at the clear-cut fenced site, where pioneer species such as Mallotus japonicus were found. A few seedlings of Q. serrata were found at each treatment site, and no Q. variabilis was recorded. The emergence of Q. serrata seedlings was explained by their location at the slope and not by the treatment. Moreover, many sprouts of Q. serrata and Q. variabilis were observed at the clear-cut fenced site. Although further monitoring is needed, clear-cutting and fencing appear to be an effective method for the rehabilitation of depleted forests.

Sprouting capacity of Quercus serrata Thunb. and Quercus acutissima Carruth. after cutting canopy trees in an abandoned coppice forest

ABSTRACTRejuvenation by sprouting is a possible solution to prevent abandoned coppice forests in Japan from outbreaks of oak wilt disease. Applying this approach requires examining the sprouting capacity of large-sized oak trees. Therefore, the present study investigated the effects of stump size, sprout characteristics (emerging time and origin position), and environmental factors (slope, convexity, soil moisture, soil net nitrogen mineralization rate (Net-NMR) and canopy closure) on sprout regeneration of the two widely distributed oaks in Japan, Quercus serrata and Quercus acutissima, in the first growing season after cutting. In November 2013, a study plot (40 × 90 m) was set, and canopy trees within the plot and edge areas were cut. We recorded sprout emergence, sprout origin position, sprout survival, and length from May to October 2014. Our data indicated that both species (ca. 60 years old) have not yet lost their ability of sprouting. In Q. acutissima, the sprouting probability increased with light availability and was higher in concave area, and its number of living sprouts was positively related to stump diameter. In Q. serrata, the number of living sprouts increased with light availability. Sprouts emerged earlier and/or originated from the lower part of stump exhibited a higher survival probability. Emerging time substantially influenced sprout growth pattern and its effect followed a similar tendency in both species. Our results evidence that the ability of sprouting and the number of living sprouts might not be reduced in large-sized trees, and the increasing of light availability could promote sprout regeneration.

Pest categorisation of Bretziella fagacearum.

Following a request from the European Commission, the EFSA Plant Health (PLH) Panel performed a pest categorisation of Bretziella fagacearum, a well‐defined and distinguishable fungal species of the family Ceratocystidaceae. The species was moved from the genus Ceratocystis to a new genus Bretziella following phylogenetic analysis of the species and its close relatives. The former species name Ceratocystis fagacearum is used in the Council Directive 2000/29/EC. The pathogen is regulated in Annex IAI as a harmful organism whose introduction into the EU is banned. B. fagacearum is only reported from the USA, where it causes a wilt disease on Quercus spp. Other hosts are reported based on inoculation trials, although Chinese chestnut (Castanea mollissima) is reported to be naturally infected. No North American oak species has been found to be immune to the disease. The European oak species Quercus robur, Quercus petraea and Quercus pubescens were found to be susceptible in inoculation experiments. The pest could enter the EU via wood (with and without bark, including wood packaging material), plants for planting and cut branches. Hosts and favourable climatic conditions are common in the EU, thus facilitating establishment. The pest would be able to spread following establishment by means of root grafts, insect vectors and movement of wood, plants for planting and other means. The pest introduction would have impacts in woodland and plantations, as oak wilt disease is often lethal in a short period of time. Wood treatment (debarking, kiln drying, fumigation), prompt removal of affected trees and creating root‐free zones between affected and healthy stands are available control measures. The main knowledge gaps concern (i) the survival of the fungus in wood during transport and the association with propagation material, (ii) the presence of suitable vectors in Europe and (iii) the relative susceptibility of the oak species native to Europe under natural conditions. The criteria assessed by the Panel for consideration as a potential quarantine pest are met. For regulated non‐quarantine pests, the criterion on the pest presence in the EU is not met.