ABSTRACT The combination of geographical factors (climate, slope, orientation, lithology, water availability, etc.) and the pathogenicity of agents such as the oomycete from the kingdom Straminopile Phytophthora or Pythium species causes the plant disease known as oak decline in the Iberian Peninsula. Leaving aside the presence of the pathogen, the aim of the study is to analyse the role played by geographical parameters in the development of this disease and to determine which ones have the greatest influence on its spread. The data were obtained from three Dehesas in the southern foothills of the Sierra de Guadarrama (Madrid, Spain). The time scale of analysis was 2006, 2011, 2014, 2020 and 2024. The geographical factors studied were altitude, slope, aspect, topographic wetness index, distance from rivers and distance from other affected trees. The results of the research showed a significant increase in disease in the three study areas. In addition, south‐southeast (S, SE) orientation, proximity to rivers, and distance from affected holm oaks were identified as geographical factors associated with holm oak decline. Given the loss of Quercus forest mass caused by the spread of the oak decline disease detected in several countries, including Spain, it becomes necessary to adequately understand the different factors that contribute and, in some cases, are the cause of the spread of the disease, as well as to identify any inhibiting factors.
ABSTRACT The invasive fungal pathogen Colletotrichum salicis , the causal agent of willow anthracnose and shoot blight, was first recorded to cause massive damage to willow in the Czech Republic in 2002 on Salix euxina . Since then, the pathogen has been repeatedly documented also in other willow species (e.g., S. caprea , S. cinerea , S. viminalis ) with the most severe damage occurring on Salix matsudana ‘Tortuosa’, which appears to be highly susceptible. Typical symptoms on infected hosts include necrotic lesions on young shoots, shoot dieback, premature defoliation and crown dieback, especially in their lower part. Disease occurrence and severity are strongly associated with inversion‐prone sites and with cold, rainy weather during spring, which promotes prolonged tissue wetness and delayed maturation of current‐year shoots. Based on currently available records, C. salicis represents an underestimated threat to willow stands in the Czech Republic. This short communication documents its occurrence, host range, impact and basic information about its ecology and disease epidemiology and highlights the need for systematic monitoring and precise diagnosis to better assess its current distribution and potential ecological consequences. The increase in the importance of this species may be associated with recent spread of willow species, especially in riparian vegetation, where ash, elm and alder have retreated due to damage by invasive pathogens.
ABSTRACT Emergent forest Phytophthora pathogens are routinely managed in a context of uncertainty where basic epidemiological understanding must be developed alongside disease management experiments. Phytophthora agathidicida causes the emergent disease kauri dieback, which threatens kauri ( Agathis australis ), a southern‐hemisphere conifer comprising some of the world's largest trees. Disease management often includes phosphite injections to reduce kauri susceptibility and slow or prevent spread between invaded and uninvaded stands. We adapt an existing spatially‐explicit and multi‐host forest epidemiological model (SODDr) to understand where incompletely understood treatment and epidemiological mechanisms may result in disease emergence across a treated host barrier. We parameterize our model with published data to evaluate three key areas of uncertainty: (1) the impact of transmission from secondary hosts, (2) the epidemiological impact of phosphite treatments at the host level, and (3) the width (treatment area) of phosphite chemical barriers. Our model experiments routinely demonstrated the potential for unknown secondary hosts to overwhelm phosphite treatment benefits, including any secondary hosts that support relatively little sporulation. Also, it is unclear if phosphite treatments cure trees of infection and reduce transmission in real systems however, in the model when treated trees remain infected the barrier is rapidly overcome. Lastly, increasing the width of the disease treatment area resulted in consistent slowing of disease spread in the model landscape, regardless of the other factors. These results were consistent in a model landscape with uniform host densities and in a follow‐up simulation of 2250 unique host landscapes with random host distribution. Our analysis suggests understanding the outcome of chemical treatment at the individual tree level along with a robust understanding of secondary host competency will be critical to effective kauri dieback management.
The combined use of Heterobasidion partitiviruses HetPV13-an1 and HetPV15-pa1 is considered a promising biocontrol approach against Heterobasidion root and butt rot. Both viruses mediate debilitating effects in many Heterobasidion isolates and are transmitted efficiently in laboratory conditions. In this investigation, we conducted transmission experiments in a natural substrate (wood billets incubated outdoors) and the natural habitat (spruce stumps with pre-existing H. parviporum infection) using H. parviporum isolates as donors and the indigenous strains as recipients. The overall transmission rates of HetPV13-an1 and HetPV15-pa1 were high in wood billets and slightly lower in naturally infected stumps, although still sufficient for biocontrol.
Global change and associated abiotic stresses, such as drought and heat waves, are increasingly predisposing forest trees to fungal pathogens. Many of these pathogens persist in a latent state within their hosts, hindering early detection and limiting accurate assessments of their current distribution. The fungus Cryptostroma corticale, the causal agent of the Sooty Bark Disease (SBD) on maple trees, is one such organism: it can remain latent within the host then become pathogenic and sporulate under abiotic stress. The fungus then colonises weakened trees, leading to dieback and mortality. Despite its emergence across Europe and the North American West Coast, there is a lack of knowledge about its latent distribution within host trees and the reliability of diagnostic approaches. In this study, we investigated the presence of C. corticale within healthy-looking sycamore maples, sampling at different tree heights and depths. During sampling, we observed numerous stains within the vascular tissues which were associated with the presence of C. corticale, particularly in the lower trunk, even though stains were more frequently observed in branches. Greenish stains were strongly correlated with fungal detection. The pathogen was predominantly detected at the collar and at 1.30-m height, suggesting that sampling at 1.30 m is a reliable proxy for rapid assessment without felling the tree. Our findings indicate that latent infections are widespread, since almost all sampled healthy-looking trees tested positive for the pathogen. This work shows that latent presence of C. corticale within infected maple stands is high and could potentially trigger severe outbreaks under abiotic stress conditions. An efficient survey method based on sampling the outer 1 cm of wood and bark from the trunk at 1.30 m above ground would improve monitoring and management of this emerging pathogen.
Pine wilt disease (PWD) caused by the pinewood nematode Bursaphelenchus xylophilus threatens subtropical pine plantations, yet family-level phenotyping remains scarce for Pinus elliottii and its hybrids with P. caribaea. We inoculated 176 two-year-old seedlings representing 22 breeding families (11 P. elliottii; 3 P. elliottii & times; P. caribaea var. caribaea; 8 P. elliottii & times; P. caribaea var. hondurensis) with a virulent nematode isolate and scored ordinal disease severity at 17 time points over 132 days, with mortality tracked to 9 months. Mixed models tested taxon effects and family effects nested within taxa. Taxa differed mainly in symptom onset, disease severity trajectories and mortality timing: P. elliottii developed symptoms later and showed lower mid-stage severity, but mortality accumulated earlier than in the hybrids, and differences diminished by 9 months. Across families, time to first symptom, integrated disease burden, and fixed-time mortality showed limited differentiation, whereas mid-stage severity (41-55 days post inoculation) provided more consistent within-taxon differentiation. These results highlight distinct response dynamics among taxa and identify a candidate mid-stage phenotyping window for breeding-oriented screening under the present assay conditions.
ABSTRACT Diseases associated with Botryosphaeriaceae have a wide host range, including plantation and fruit trees, as well as many ornamental plants. These fungi have a global distribution and occur across a wide variety of environments. DNA‐based techniques have revolutionized the characterization of the Botryosphaeriaceae , as is true for other groups of fungi. In China, the application of these tools has resulted in more than a hundred first reports of species including novel taxa. The aim of this review is to summarize this growing understanding of the taxonomy, distribution and pathogenicity of the Botryosphaeriaceae in China. Between 2007 and 2024, 321 papers have been published that include DNA sequence data for these Botryosphaeriaceae . These studies have recorded at least 144 species residing in 16 genera in 156 genera of 83 families. These records are from 31 of 34 provincial‐level regions of China, covering temperate, subtropical and tropical zones. The data illustrate the ability of the Botryosphaeriaceae to adapt to a wide diversity of environments. Furthermore, considering their importance in the context of climate change and especially for those species having a wide distribution and/or high levels of virulence.
Macaranga peltata (Roxb.) M & uuml;ll. Arg., a tropical tree widely distributed in South and Southeast Asia, is an ecologically and economically important species used for timber, traditional medicine, afforestation and agroforestry. During seedling evaluations at the College of Forestry, Thrissur, Kerala, India, characteristic symptoms of leaf blight were observed. A fungal isolate was consistently recovered from diseased tissues through standard tissue isolation methods. Cultural and morphological characteristics, together with multi-gene phylogenetic analyses comprising the internal transcribed spacer (ITS), Glyceraldehyde-3-phosphate dehydrogenase (GAPDH), the translation elongation factor 1-alpha region (TEF1 alpha) and Alternaria major allergen gene (Alt a 1), confirmed the pathogen as Alternaria jacinthicola. The pathogenicity of the isolate was validated through inoculation studies by fulfilling Koch's postulates. The present investigation constitutes the first confirmed report of Alternaria jacinthicola causing leaf blight on Macaranga peltata in India. Since A. jacinthicola is expanding its host range and posing a new threat to tropical forest nurseries, foresters need to implement regular monitoring and adopt suitable management interventions.
Cinnamomum camphora root rot was detected in Ji'an County, Jiangxi Province from 2023 to 2024. To identify the pathogen, root samples from diseased trees were collected. Tissue isolation method was employed to isolate and purify the pathogens causing camphor tree root rot. Fusarium solani was identified as the causative agent through morphological characterisation and multigene phylogenetic analysis (using ITS, EF-1 alpha and RPB2), further confirmed by in vitro artificial inoculation. F. solani led to leaf chlorosis and root browning on C. camphora seedings in pots, consistent with symptoms observed in the field. This study is the first to report F. solani as the cause of root rot on C. camphora, underscoring how this pathogen causes substantial losses to economically valuable trees due to the absence of prevention and mitigation strategies.
Eutypella parasitica, the causal agent of Eutypella canker on maple species, is an invasive forest pathogen recently introduced to Europe. Due to the wide distribution of susceptible Acer species, further spread across European forests is expected. To better understand factors driving the spread of this emerging forest disease, we aimed to identify the key environmental and spatial drivers of Eutypella canker occurrence focusing on Acer pseudoplatanus. For this purpose, we surveyed the presence and absence of Eutypella canker at 232 forest sites in southeastern Germany and analysed climatic, site-related and spatial factors using a binomial generalised linear model (GLM). Eutypella canker was detected at 57 sites, while 175 forest sites showed no symptoms. The probability of disease occurrence increased with higher precipitation and moderate temperatures during the vegetation period from May to September. In addition, forests located in close proximity to water bodies such as rivers and lakes exhibited a significantly higher probability of infection. Spatial proximity to already infected forest sites emerged as the strongest predictor of disease occurrence, indicating pronounced spatial clustering and suggesting active spatial spread processes. Our results demonstrate that both climatic suitability and spatial connectivity are key determinants of Eutypella canker establishment. These findings provide an important basis for risk assessment and targeted monitoring of this emerging invasive forest disease in Europe.
Since its introduction, ash dieback has been a disease affecting ash (Fraxinus excelsior) stands across nearly their entire range. As the disease cannot be contained, various options for mitigating its severity have been explored in numerous studies. It has frequently been proposed that ash, particularly in dense pure stands, is more severely impacted by the disease. Additionally, it has been claimed that the presence of mixed tree species might have a species-specific effect in mitigating disease progression. To investigate the impact of admixed tree species, we conducted greenhouse experiments in which ash trees were grown under varying quantities of infected ash and mixed tree species leaf litter. The objective was to assess the effect of admixed tree species based on pathogen spore production and the assessment of disease symptoms. The mixed tree species used in the experiments were beech (Fagus sylvatica), sycamore (Acer pseudoplatanus) and winter lime (Tilia cordata). Spore production from the infected leaf litter in the greenhouse cabins followed patterns broadly consistent with previous field observations. We demonstrated that spore pressure in the cabins depended on the applied quantity of infected ash leaf litter and that the mixed tree species exerted no further influence. The number of infected shoots on an ash tree correlated with both its total number of shoots and the quantity of infected ash leaf litter. The number of shoots was considered an indicator for leaf area and thus the tree's potential to become infected. For stem necroses, only the quantity of infected ash leaf litter was found to be decisive. We conclude that the milder progression of ash dieback in mixed stands is primarily due to a dilution effect caused by the presence of mixed tree species. No additional effects of the three mixed tree species on spore production or disease progression were observed in our study.
Bacterial blight caused by Erwinia psidii, has become an emerging and severe threat to Eucalyptus production in Brazil. Breeding for resistance remains the most effective strategy for disease management, yet the reliability of early-stage screening under controlled conditions as a predictor of field performance has not been fully validated. This study aimed to evaluate the predictive reliability of early-stage selection of resistant genotypes under standardized greenhouse inoculation and symptom expression in field trials under natural high pathogen inoculum pressure. A set of Eucalyptus clones was assessed for disease severity in both conditions, and statistical analyses were performed to determine the predictive value of controlled-environment phenotyping. Genetic parameters were estimated using REML/BLUP, and the correlation between early and field evaluations was analysed. The results revealed high genetic variability and broad-sense heritability ( = 0.98 in greenhouse; = 0.83-0.92 in field). A significant correlation (r = 0.73) was observed between greenhouse and field responses, with the early screening showing the highest accuracy for correctly classifying resistant clones. Greenhouse-based screening provides a strong indication of field resistance, highlighting its utility for early selection in breeding programs. These findings reinforce the role of integrated screening strategies in accelerating development of resistant clones, ensuring sustainable management of E. psidii in Eucalyptus field stands.
Tectona grandis (teak) is a tree species highly appreciated for its high-quality hardwood and versatile industrial applications. Despite clonal teak plantations showing several advantages, such as reduced rotation time and increased wood volume production, the genetic uniformity of plantations makes them more susceptible to diseases. Ceratocystis wilt caused by Ceratocystis manginecans has been the most prevalent disease on teak plantations, reducing tree growth rate, wood quality and value. Planting resistant genotypes is the most effective measure to mitigate losses caused by the disease. Thus, this work aimed to assess the resistance to Ceratocystis wilt of 12 teak clones commercially planted in Brazil, as well as the inheritance of resistance in teak open-pollinated families. Five teak clones exhibited resistance to Ceratocystis wilt, and all investigated open-pollinated teak families segregated resistance. The findings support the interpretation that resistance to Ceratocystis wilt in teak is a quantitative trait with additive gene effects in determining this trait. The information obtained in this work is an important contribution to directing the efforts of teak breeding programs in the attempt to reduce the losses caused by Ceratocystis wilt.
Phytophthora monitoring was carried out across 20 beech stands in southern Belgium. Twenty dominant or co-dominant trees were observed at all 20 sites. In 2022, more than half of these trees displayed crown transparency and branch dieback. In each site, soil samples were collected from three trees representing different levels of decline to assess the presence of Phytophthora in the fine roots. Baiting tests were performed in 2019 (9 sites) and 2021 (20 sites). Among all baited samples, P. cinnamomi was the only Phytophthora species recovered. It was found in a single site (site 14, Mormont) located in a very humid area, in 2021, and its presence was confirmed in 2025. To our knowledge, this is the first report of this species in beech forests in Belgium. All baiting results at the other 19 sites were negative. Baiting tests conducted by artificially infecting the soils from eight of the 20 sites with various Phytophthora species associated with beech decline in Europe were negative, except for P. cinnamomi, showing a different behaviour of this species according to the characteristics of the soils studied. Replacing demineralised water with filtered river water or a seaweed solution for baiting tests, both of which increase the pH of the soil suspension, restored the infection potential of the Phytophthora species studied, as reflected by necrosis on baited leaves. However, when soils that had previously tested negative using demineralised water were reanalysed with filtered river water or a seaweed solution as baiting media, the baited leaves remained symptomless. These trials demonstrate that soils with a low pH limit the infective potential and the occurrence of Phytophthora. They also highlight the higher risk represented by P. cinnamomi for Belgian beech forests growing in acidic soils.
Lecanosticta acicola is a fungal pathogen that causes brown spot needle blight (BSNB). It primarily impacts the genus Pinus and has been introduced to much of the Northern Hemisphere. Brown spot needle blight causes a reduction of leaf area and photosynthetic capacity that can lead to reduced growth and mortality in extreme cases. In the southeastern USA, the disease has historically primarily impacted grass stage longleaf pine (Pinus palustris). Around 2015, large areas of plantation loblolly pine (Pinus taeda) were found to be infected with L. acicola, which is outside of historic norms for the pathogen. The aims of this research were to get a first estimate of the impact of the disease on loblolly pine plantations and outline methods for managers to model growth with their specific stand characteristics. We used the 3-PG model (Physiological Processes Predicting Growth) to estimate the impact of defoliation caused by the disease. We found the season of defoliation did not have an impact on stem volume and leaf area index recovered to undefoliated levels approximately 5 years following the last defoliation event. Increasing defoliation levels reduced stem volume growth as expected with 1 to 5 consecutive years of defoliation delaying stand development by 0.1 to 1 year. We find that defoliation delays stand development and that this delay is sustained going forward. Lower productivity sites had a larger reduction in stand volume highlighting the need for a measure of stand productivity in estimating the impact of BSNB defoliation and the need to include stand productivity in future models. This framework is primitive but provides managers with the ability to input their stand characteristics and get more specific estimates for growth loss due to BSNB defoliation and provides the ability to model different disease scenarios to better manage losses due to this emerging disease phenomenon.
Beech leaf disease (BLD) is a foliar disease of American beech (Fagus grandifolia) that manifests as gall symptoms in leaves caused by infestations from Litylenchus crenatae ssp. mccannii, a plant-parasitic nematode. As the disease progresses, infestations lead to bud abortion, crown deterioration and branch dieback. While BLD is known to impair leaf function, the impacts of the disease on tree carbon allocation and growth are unresolved. Here, we sampled three forest stands across a gradient of disease severity to assess how BLD influences the storage of non-structural carbohydrates (NSC) across different tissue pools (root, bole and twigs), used tree rings to estimate growth declines associated with the onset of BLD infestation and evaluated the fine root ectomycorrhizal communities. Our data show that BLD can negatively impact NSC storage across tissue pools in stands exhibiting both low- and high-severity infestation. Diminished starch content with respect to the asymptomatic stand was shown to precede any reduction in growth, measured via post-infestation basal area increment at the low-severity stand (1-2 years of infestation). Growth reductions at the high-severity stand (3+ years post infestation) were significant and coincided with low NSC content, though mortality was not observed among any mature trees. Root-associated fungal community composition differed significantly among sites, with a trend towards reduced diversity in more severely impacted trees. Our results suggest that BLD disrupts carbon allocation and storage in beech trees, potentially compromising their resilience to future stressors. The complex interplay between nematode infestation, fungal community shifts and altered carbohydrate dynamics highlights the multifaceted nature of BLD and its potential long-term consequences for beech forests.
Ganoderma gibbosum is a wood-decaying basidiomycete with a complex taxonomic history and has been inconsistently reported from India, often without adequate morphological or molecular verification. In the present study, G. gibbosum is confirmed from India on three previously unreported hosts-Acrocarpus fraxinifolius, Morus alba and Cupaniopsis anacardioides-based on detailed macro- and micromorphological examinations and phylogenetic analyses of the internal transcribed spacer (ITS) region. Maximum likelihood and Bayesian inference analyses consistently resolved the newly collected Indian specimens within a clade comprising authenticated G. gibbosum specimens from Asia, including India, China, Japan and Korea. These findings clarify the taxonomic status of G. gibbosum in India and substantially expand its known host range and geographic distribution.
The powdery mildew fungus Erysiphe quercicola (Erysiphaceae) has a complex taxonomic history that has long complicated assessments of its geographic distribution and host associations. Although knowledge of the global host range of this species has expanded substantially over the past two decades, sequencing-confirmed records from North America remain scarce, and despite its recognition as an introduced pathogen, the timing of introduction and the geographic extent and host range of E. quercicola in the United States are poorly understood. In this study, herbarium specimens of E. quercicola from North America, spanning both historical and contemporary collections, were examined using molecular phylogenetic approaches. Specimens collected from multiple Quercus species across several regions of the United States, as well as from related hosts within the Fagaceae, were evaluated. Sequence data confirm the presence of E. quercicola in North America on Quercus species based on herbarium specimens collected as early as 1944, as well as on mango (Mangifera indica; Anacardiaceae) in Florida from material collected in 1935. These records raise the possibility of historical introduction pathways associated with cultivated hosts, potentially from the horticulturally important mango tree (M. indica); however, additional multilocus phylogenetic analyses and host range inoculation experiments will be required to determine whether powdery mildew populations infecting mango and Quercus in North America represent the same lineage. Additional sequencing-confirmed records document the species on multiple native oak species representing different sections of Quercus including Q. bicolor, Q. gambelii, Q. garryana, Q. geminata, Q. kelloggii, Quercus & times; jolonensis and Q. macrocarpa as well as on Notholithocarpus densiflorus. Together, these findings clarify the long-term presence of E. quercicola in the United States, expand knowledge of its North American host range, and demonstrate the value of herbaria for reconstructing the invasion history of forest pathogens.
Stump removal has been used to control impacts from other root diseases but to the best of our knowledge our study is the first to report long-term results of stumping to control Tomentosus root disease. Tomentosus root disease (Onnia tomentosa) causes root and butt rot and is the dominant pathogen of interior spruce (Picea engelmanni & times; Picea glauca) in central British Columbia, Canada. We went to considerable effort to quantify the incidence and distribution of infected stumps from the prior stand and to account for it in our study design. Despite this, we found a poor relationship between both the basal area of pitted decay and the number of infected stumps and the incidence of disease in planted spruce. After 27 growing seasons, we found trees that had become infected with O. tomentosa by Age 22 grew significantly less (1.7 m) than uninfected trees. We found trees planted in stumped plots grew significantly larger in both height and diameter for several years but were no larger than trees in the control by the 27th growing season. Most importantly, after 28 years, we found the stumping treatment failed to significantly reduce the incidence of infection and mortality in planted spruce trees.
Oak wilt, caused by Bretziella fagacearum, is a destructive vascular disease of oaks in North America, yet fine-scale spatial localisation of the pathogen in host tissues and on insect vectors remains poorly characterised. In this study, we developed and validated a species-specific fluorescence in situ hybridisation (FISH) probe targeting the 28S rDNA of B. fagacearum and evaluated its capacity to detect and localise the pathogen in naturally infected red oak (Quercus rubra) tissues and on sap beetle vectors (Nitidulidae). Probe specificity was confirmed through fluorescence in situ hybridisation (FISH) and confocal laser scanning microscopy (CLSM), which showed strong hybridisation to B. fagacearum and no detectable signal in closely related Ceratocystidaceae. FISH successfully visualised ascospores on Carpophilus sayi collected from sporulating mats, with consistent localisation on terminal abdominal sternites and occasionally on mesoventral grooves, legs and antennae. Within oak twig tissues, FISH detected B. fagacearum hyphae predominantly in vessel elements, fibres, and occasionally in axial and ray parenchyma. In infected petioles, hyphae occurred in xylem vessels, collenchyma, and parenchyma, demonstrating pathogen presence beyond midrib tissues. Overall, this study establishes CLSM-FISH as a powerful visualisation tool for investigating the host-pathogen-vector interactions of the oak wilt disease.
