Bursaphelenchus Xylophilus Research Articles

A natural intra‐specific hybridization between populations of B. mucronatus with European and East Asian genotypes, in pine forests

AbstractBursaphelenchus mucronatus Mamiya & Enda, 1979 is a wood nematode widely distributed over Palearctic coniferous forests. It has two subspecies, that is, B. mucronatus mucronatus and B. mucronatus kolymensis, which present molecularly different East Asian and European genotypes, respectively. The European subspecies is found mainly in Europe and Siberia, while the East Asian subspecies occupies mostly Eastern regions of Asia. However, local isolates of both subspecies have been occasionally reported from various localities in Europe and Asia. Our field isolation and molecular (DNA ITS‐RFLP) identification of 21 recently collected populations of B. mucronatus revealed only 4 isolates representing clearly East Asian or European genotypes, while the remaining 17 isolates showed intermediate genotypes with electrophoretic band characters of both the above types. Further individual crossbreeding, in vitro, of nematodes representing European, East Asian, and intermediate genotypes provided experimental evidence for the process of intraspecific hybridization between both subspecies, spontaneously taking place in the forest. Such a widening of the B. mucronatus genetic variation may have its effect on a range of reported in the literature direct interactions between this native, nonpathogenic nematode species and the genetically similar, causative agent of the pine wilt disease B. xylophilus which can colonize the same host trees, use the same insect vectors, compete, and crossbreed inter‐specifically.

Neuronal cell protective effects of phenolic compounds derived from steam exploded nematode-infected pine

Pine wilt disease is one of the most serious forest diseases that kills pine trees. Most of the nematode-infected pines are fumigated or locally incinerated and are thus not appropriately utilized. This study explored methods to utilize abandoned nematode-infected pines. The chemical compositions of healthy and nematode-infected pines were analyzed, and the neuroprotective effects of phenolic compounds extracted after steam explosion treatment were investigated. In terms of chemical composition, the nematode-infected pine chips suffered more damage from the steam explosion treatment than the healthy pine chips. In addition, the total phenolic compound content showed a clear difference depending on the presence of infection and steam explosion conditions. The maximum total phenolic compound content of extracted ethanol was found when the nematode-infected pine chip was subjected to steam explosion with a severity factor (Ro) of 3.82. The steam exploded pine extract of 10 μg/mL inhibited glutamate-induced early apoptotic cell death compared to cells treated with 10 mM glutamate alone. These results suggested that steam-exploded pine can be used as an effective natural material for neuronal cell protection.

Rapid and Efficient Molecular Detection of Phytophthora nicotianae Based on RPA-CRISPR/Cas12a

Phytophthora nicotianae is a global and polyphagous pathogen with a wide host range. P. nicotianae can infect Areca catechu, Durio zibethinus L., Psidium guajava L., Hevea brasiliensis, and other tree species. The pathogen is capable of inducing butt rot and affecting aerial parts, including stems, leaves, and fruits. Compared to other Phytophthora species, P. nicotianae is more adaptable to abiotic stress. In this study, recombinase polymerase amplification (RPA) in combination with the CRISPR/Cas12a system was used for the detection of P. nicotianae, and achieved rapid and efficient detection of P. nicotianae. The assay was highly specific to P. nicotianae. All 4 tested isolates of P. nicotianae yielded positive results, whereas 30 isolates belonging to 17 other Phytophthora species, 8 fungal species, and 4 Bursaphelenchus xylophilus vermicules lacked detection. Under the conditions of 37 °C, after 20 min of RPA reaction and 25 min of Cas12a cleavage, a DNA concentration as low as 10 pg·μL−1 could be detected. In addition, it detected P. nicotianae from artificially inoculated leaves of Fatsia japonica. In this study, a novel method was established for the efficient and accurate detection of P. nicotianae based on the combination of RPA and the CRISPR/Cas12a system.

A pioneer nematode effector suppresses plant reactive oxygen species burst by interacting with the class III peroxidase.

Bursaphelenchus xylophilus is the pathogen of pine wilt disease, which can devastate the pine forest ecosystem. Usually, plant cells generate reactive oxygen species (ROS)as a defensive substance or signalling molecules to resist the infection of nematodes. However, little is known about how B. xylophilus effectors mediate the plant ROS metabolism. Here, we identified a pioneer B. xylophilus Prx3-interacting effector 1 (BxPIE1)expressed in the dorsal gland cells and the intestine. Silencing of the BxPIE1 gene resulted in reduced nematode reproduction and a delay in disease progression during parasitic stages, with the upregulation of pathogenesis-related (PR)genes PtPR-3(class Ⅳ chitinase) and PtPR-9(peroxidase). The protein-protein interaction assays further demonstrated that BxPIE1 interacts with a Pinus thunbergii class III peroxidase (PtPrx3), which produces H2O2 under biotic stress. The expression of BxPIE1 and PtPrx3 was upregulated during the infection stage. Furthermore, BxPIE1 effectively inhibited H2O2 generating from class III peroxidase and ascorbate can recover the virulence of siBxPIE1-treated B. xylophilus by scavenging H2O2. Taken together, BxPIE1 is an important virulence factor, revealing a novel mechanism utilized by nematodes to suppress plant immunity.

Genetic Diversity and Population Structure of Bursaphelenchus xylophilus in Guangdong, Guangxi, and Jiangsu Provinces in China

This study aimed to investigate the genetic structures of pine wood nematodes (PWNs, Bursaphelenchus xylophilus (Steiner & Buhrer) Nickle)), in Guangdong (GD), Guangxi (GX), and Jiangsu (JS) Provinces (the major PWN dispersal centers). Furthermore, we also explored potential migration routes among the different provinces in order to provide insights into the epidemic source of PWNs in the three provinces in China. We re-sequenced a total of 241 PWNs collected from the above provinces using next-generation sequencing to obtain raw genomic data. Bioinformatics analysis was used to identify the SNPs, genetic structures, and selective sweeps of the PWNs. The results indicate that the PWNs from these three provinces can be classified into five groups (A, B, C, D, and E), among which the genetic variations are significant. All PWN strains from JS were exclusively found in Group A. The PWNs in Groups B and C were composed of strains from GD and GX, while Groups D and E comprised only GD strains. Introgression analysis identified two possible pathways: (1) from Group A to Group B-GX and (2) from Group E to Group D. Selective sweep analysis showed that in Groups B and C, the candidate genes of Group B were mainly related to pectin lyase activity.

The Growth-Promoting and Colonization of the Pine Endophytic Pseudomonas abietaniphila for Pine Wilt Disease Control.

In this study, we focused on evaluating the impact of Pseudomonas abietaniphila BHJ04 on the growth of Pinus massoniana seedlings and its biocontrol efficacy against pine wilt disease (PWD). Additionally, the colonization dynamics of P. abietaniphila BHJ04 on P. massoniana were examined. The growth promotion experiment showed that P. abietaniphila BHJ04 significantly promoted the growth of the branches and roots of P. massoniana. Pot control experiments indicated that strain BHJ04 significantly inhibited the spread of PWD. There were significant changes in the expression of several genes related to pine wood nematode defense in P. massoniana, including chitinase, nicotinamide synthetase, and triangular tetrapeptide-like superfamily protein isoform 9. Furthermore, our results revealed significant upregulation of genes associated with the water stress response (dehydration-responsive proteins), genetic material replication (DNA/RNA polymerase superfamily proteins), cell wall hydrolase, and detoxification (cytochrome P450 and cytochrome P450 monooxygenase superfamily genes) in the self-regulation of P. massoniana. Colonization experiments demonstrated that strain BHJ04 can colonize the roots, shoots, and leaves of P. massoniana, and the colonization amount on the leaves was the greatest, reaching 160,000 on the 15th day. However, colonization of the stems lasted longer, with the highest level of colonization observed after 45 d. This study provides a preliminary exploration of the growth-promoting and disease-preventing mechanisms of P. abietaniphila BHJ04 and its ability to colonize pines, thus providing a new biocontrol microbial resource for the biological control of plant diseases.

Conversion of infected pine wood into energy charcoal material based on a transportable carbonization system

To prevent the spread of pine wilt disease (PWD), a transportable carbonization equipment was designed for in-situ treatment of infected pine wood (IPW). The equipment killed all pine wood nematodes (PWNs) in IPW when carbonization temperature was up to 200 °C. The optimal laboratory process of infected pine wood charcoal (IPWC) was carbonization temperature of 500 °C, heating rate of 3 °C min−1 and holding time of 0 min. Based on the optimal laboratory process, the transportable carbonization equipment produced IPWC with a fixed carbon content of 79.82%, and ash content of 1.14% and a moisture content of 7.83%, which meets the requirements of EN 1860-2:2005(E) standard. The economic efficiency of incineration (T1 mode), crushing (T2 mode), and transportable carbonization (T3 mode) was evaluated. For each ton of IPW treatment, the profit generated was −75.48 USD in T1 mode, 26.28 USD in T2 mode, and 51.91 USD in T3 mode. T3 mode had the highest economic efficiency. These findings will be helpful to provide guidance for the control of PWD and value-added utilization of IPW.Graphical

Biomass-Based, Dual Enzyme-Responsive Nanopesticides: Eco-friendly and Efficient Control of Pine Wood Nematode Disease.

Pine wood nematode (PWN) disease is a globally devastating forest disease caused by infestation with PWN, Bursaphelenchus xylophilus, which mainly occurs through the vector insect Japanese pine sawyer (JPS), Monochamus alternatus. PWN disease is notoriously difficult to manage effectively and is known as the "cancer of pine trees." In this study, dual enzyme-responsive nanopesticides (AVM@EC@Pectin) were prepared using nanocoating avermectin (AVM) after modification with natural polymers. The proposed treatment can respond to the cell wall-degrading enzymes secreted by PWNs and vector insects during pine tree infestation to intelligently release pesticides to cut off the transmission and infestation pathways and realize the integrated control of PWN disease. The LC50 value of AVM@EC@Pectin was 11.19 mg/L for PWN and 26.31 mg/L for JPS. The insecticidal activity of AVM@EC@Pectin was higher than that of the commercial emulsifiable concentrate (AVM-EC), and the photostability, adhesion, and target penetration were improved. The half-life (t1/2) of AVM@EC@Pectin was 133.7 min, which is approximately twice that of AVM-EC (68.2 min). Sprayed and injected applications showed that nanopesticides had superior bidirectional transportation, with five-times higher AVM contents detected in the roots relative to those of AVM-EC when sprayed at the top. The safety experiment showed that the proposed treatment had lower toxicity and higher safety for nontarget organisms in the application environment and human cells. This study presents a green, safe, and effective strategy for the integrated management of PWN disease.

Pine Wilt Disease Segmentation with Deep Metric Learning Species Classification for Early-Stage Disease and Potential False Positive Identification

Pine Wilt Disease poses a significant global threat to forests, necessitating swift detection methods. Conventional approaches are resource-intensive but utilizing deep learning on ortho-mapped images obtained from Unmanned Aerial Vehicles offers cost-effective and scalable solutions. This study presents a novel method for Pine Wilt Disease detection and classification using YOLOv8 for segmenting diseased areas, followed by cropping the diseased regions from the original image and applying Deep Metric Learning for classification. We trained a ResNet50 model using semi-hard triplet loss to obtain embeddings, and subsequently trained a Random Forest classifier tasked with identifying tree species and distinguishing false positives. Segmentation was favored over object detection due to its ability to provide pixel-level information, enabling the flexible extension of subsequent bounding boxes. Deep Metric Learning-based classification after segmentation was chosen for its effectiveness in handling visually similar images. The results indicate a mean Intersection over Union of 83.12% for segmentation, with classification accuracies of 98.7% and 90.7% on the validation and test sets, respectively.

Heat stress-induced oviposition behavioral change correlates with sperm damage in the pine sawyer beetle, Monochamus alternatus.

Global climate change is causing an increase in extreme high temperatures (EHTs), which subject insects to unprecedented stress. Behavior plasticity in response to EHTs, particularly oviposition behavior, is important for the persistence and outbreak of insect populations. Investigating the plasticity of oviposition behavior and its underlying mechanisms has theoretical importance to pest management, but knowledge gaps still remain. Herein, we characterized the reproductive traits of Monochamus alternatus, a dominant insect vector of the destructive pine wilt disease, including oviposition behavioral patterns, fecundity, offspring fitness and sperm viability, under simulated heatwave conditions in the laboratory. The results showed that (i) EHTs induced a novel oviposition behavior, whereby females deposited multiple eggs into a single groove rather than laying one egg per groove under normal condition; (ii) EHTs exerted stage- and sex-specific effects on fecundity, offspring fitness and sperm viability; and (iii) there was a significant correlation between frequency of the novel oviposition strategy and sperm viability. We hypothesized that this beetle pest has the ability to flexibly shift towards a low-cost oviposition strategy to counteract the fitness costs caused by heat stress. Taken together, these findings provide a theoretical foundation for personalized pest management strategies in the context of climate change. © 2024 Society of Chemical Industry.

Pinus thunbergii Parl. Somatic Plants' Resistance to Bursaphelenchus xylophilus Depends on Pathogen-Induced Differential Transcriptomic Responses.

Pinus thunbergii Parl. is an economically and medicinally important plant, as well as a world-renowned horticultural species of the Pinus genus. Pine wilt disease is a dangerous condition that affects P. thunbergii. However, understanding of the genetics underlying resistance to this disease is poor. Our findings reveal that P. thunbergii's resistance mechanism is based on differential transcriptome responses generated by the early presence of the pathogen Bursaphelenchus xylophilus, also known as the pine wood nematode. A transcriptome analysis (RNA-seq) was performed to examine gene expression in shoot tissues from resistant and susceptible P. thunbergii trees. RNA samples were collected from the shoots of inoculated pines throughout the infection phases by the virulent Bursaphelenchus xylophilus AMA3 strain. The photosynthesis and plant-pathogen interaction pathways were significantly enriched in the first and third days after infection. Flavonoid biosynthesis was induced in response to late infestation (7 and 14 days post-infestation). Calmodulin, RBOH, HLC protein, RPS, PR1, and genes implicated in phytohormone crosstalk (e.g., SGT1, MYC2, PP2C, and ERF1) showed significant alterations between resistant and susceptible trees. Furthermore, salicylic acid was found to aid pine wood nematodes tolerate adverse conditions and boost reproduction, which may be significant for pine wood nematode colonization within pines. These findings provide new insights into how host defenses overcame pine wood nematode infection in the early stage, which could potentially contribute to the development of novel strategies for the control of pine wilt disease.

Response analysis of Pinus sibirica to pine wood nematode infection through transcriptomics and metabolomics study.

Pinus sibirica is primarily distributed in Siberia. Owing to its excellent cold resistance and development potential, it has become an important introduced tree species in the Greater Xing'an area of China. Pine wilt disease, triggered by the pine wood nematode (PWN, Bursaphelenchus xylophilus), constitutes a profoundly critical affliction within forest ecosystems. Its incidence has extended to the northeastern region of China in recent years. To explore the potential host status of P. sibirica in the Greater Xing'an area for PWN and to elucidate the responses following inoculation, artificial inoculation, transcriptomics, and metabolomics methods were used. In the artificial inoculation experiments, quantitative analysis of nematode populations within the trees demonstrated that PWN exhibited normal growth and reproductive capabilities within P. sibirica. Subsequently, transcriptome and metabolome sequencing were conducted at four time points before disease onset (3-, 5-, 7-, and 9-days post inoculation). Gene trend analysis and differentially expressed gene screening were employed and the results indicated that genes associated with the flavonoid biosynthesis pathway exhibited predominant enrichment among the up-regulated genes. Metabolome analysis showed that the abundance of flavonoid-related metabolites in P. sibirica increased after inoculation with PWN. Integrated analysis of transcriptome and metabolome revealed that after PWN inoculation in P. sibirica, two chalcone synthase (chs) genes and a chalcone isomerase (chi) gene were significantly upregulated, and the upregulation should accumulate naringenin, pinocembrin, and apigenin to help P. sibirica resist infection of PWN. The results suggested that flavonoid biosynthesis pathway continued to respond after P. sibirica was infected with PWN and played an important role in the interaction between P. sibirica and PWN.

MYB4 is the best candidate transcription factor involved in pinosylvin stilbene biosynthesis in Pinus strobus L. cells by fungal elicitor treatment

Key messageDihydropinosylvin monomethyl ether (DPME) and pinosylvin monomethyl ether (PME) are pinosylvin derivatives that show high nematicidal activity against pine wood nematodes (PWNs). Here, we found that fungal elicitor treatment boosted the production of DPME and PME in cultured Pinus strobus L. cells and investigated the transcription factors (TFs) regulating the genes in the pinosylvin stilbenoid biosynthesis pathway.ContextThe discovery of TFs involved in the synthesis of DPME and PME provides an important clue to understanding the pinosylvin stilbenoid synthesis in pine plants.AimsWe investigated the best fungal elicitor for the production of DPME and PME and the transcriptional activities of genes involved in PME and DPME biosynthesis in P. strobus L. cells after fungal elicitor treatment.MethodsThe content of DPME and PME in P. strobus cells was examined after treatment with fungal elicitors prepared from seven different species of fungi. Moreover, the role of fungal elicitors in the transcriptional activity of genes involved in DPME and PME biosynthesis was investigated by transcriptome analysis using RNA sequencing.ResultsPenicillium chrysogenum Thorn was the most efficient fungal elicitor for the production of DPME and PME in P. strobus cells among the other fungal species. The accumulation of DPME and PME in P. strobus cells after P. chrysogenum elicitor treatment increased 12.7-fold and 23.7-fold, respectively, compared to the control. Transcriptome analysis revealed that fungal elicitor treatment resulted in enhanced transcription of the PAL, 4CL, STS, PMT, and ACC genes, which are involved in PME and DPME biosynthesis. Some transcription factors belonging to the bHLH, MYB, WRKY, and ERF families showed a high transcription rate after fungal elicitor treatment.ConclusionsWe found that the fungal elicitor is a strong inducer of the accumulation of pinosylvin derivatives in the cells of P. strobus. We selected one unigene (c133966_g3_i1 in the MYB family) as the best candidate TF that regulates the DPME and PME biosynthesis in P. strobus by transcriptome analysis.

Transcriptome analysis highlights the influence of temperature on hydrolase and traps in nematode-trapping fungi.

Pine wilt disease caused by Bursaphelenchus xylophilus poses a serious threat to the economic and ecological value of forestry. Nematode trapping fungi trap and kill nematodes using specialized trapping devices, which are highly efficient and non-toxic to the environment, and are very promising for use as biological control agents. In this study, we isolated several nematode-trapping fungi from various regions and screened three for their high nematocidal efficiency. However, the effectiveness of these fungi as nematicides is notably influenced by temperature and exhibits different morphologies in response to temperature fluctuations, which are categorized as "NA," "thin," "dense," and "sparse." The trend of trap formation with temperature was consistent with the trend of nematocidal efficiency with temperature. Both of which initially increased and then decreased with increasing temperature. Among them, Arthrobotrys cladodes exhibited the highest level of nematocidal activity and trap formation among the tested species. Transcriptome data were collected from A. cladodes with various trap morphologies. Hydrolase activity was significantly enriched according to GO and KEGG enrichment analyses. Eight genes related to hydrolases were found to be consistent with the trend of trap morphology with temperature. Weighted gene co-expression analysis and the Cytoscape network revealed that these 8 genes are associated with either mitosis or autophagy. This suggests that they contribute to the formation of "dense" structures in nematode-trapping fungi. One of these genes is the serine protein hydrolase gene involved in autophagy. This study reveals a potentially critical role for hydrolases in trap formation and nematocidal efficiency. And presents a model where temperature affects trap formation and nematocidal efficiency by influencing the serine protease prb1 involved in the autophagy process.

Epidemiological model including spatial connection features improves prediction of the spread of pine wilt disease

In recent decades, the tree killing pine wilt disease (PWD) has been spreading globally and has caused substantial damage, particularly in China, resulting in annual losses of nearly $15 billion. This disease is caused by the pine wood nematode (Bursaphelenchus xylophilus) and is transmitted by its vector insect (Monochamus spp.). However, there remains limited understanding of the factors influencing PWD transmission, especially anthropogenic factors. For the first time, we employed a dataset of propagation factors that based on the transportation of pine wood transmission and used an enhanced infectious disease dynamics method to quantitatively predict the likelihood of future PWD infections across the entire distribution range of pine trees in China. The validation results show that the risk of infection in potential areas of PWD will further increase in China, with the average risk surpassing 30% in 2023 and reaching 50% by 2025 in the study areas. Meanwhile, we observe that human factors, such as transportation of timber, are becoming the main cause of the rapid spread of PWD and require extra vigilance. By incorporating spatial connections between samples as features for PWD prediction, the Area Under the Curve (AUC) score of the model reached 0.90. This signifies a highly accurate prediction of the pivotal areas for PWD dissemination, providing valuable guidance for the precise development of prevention and control measures, and presenting innovative approaches for analogous studies.

Pest categorisation of Shirahoshizo flavonotatus.

The EFSA Panel on Plant Health performed a pest categorisation of Shirahoshizo patruelis (Voss, 1937) (Coleoptera: Curculionidae), following the commodity risk assessment of bonsai plants from China consisting of Pinus parviflora grafted on P. thunbergii, in which S. patruelis was identified as a pest of possible concern to the European Union (EU). This categorisation refers to S. flavonotatus, which is the pest's current valid scientific name. It is native to China and has never been recorded in the EU. It completes from 2 to 3 generations per year. Eggs are laid in cracks and crevices of trunks and branches with bark thickness of approximately 0.6-1.2 cm. The pest overwinters as an adult or as a mature larva under the bark. Plants for planting, wood with bark and wood products provide pathways for entry. Although the weevil has been reported to carry the nematode Bursaphelenchus xylophilus, it is not considered a vector. Climatic conditions and availability of host plants in some EU countries would allow S. flavonotatus to establish and spread. Impact on Pinus spp. is anticipated. Recognising that the weevil is reported to attack both weakened and healthy trees, there is uncertainty on the magnitude of impact. Its recorded capacity to attack non-Asian Pinus species also indicates its ability to adapt and expand the range of trees it can utilise as hosts, which could include European Pinus species. Phytosanitary measures are available to reduce the likelihood of entry and spread. S. flavonotatus meets the criteria that are within the remit of EFSA to assess for this species to be regarded as a potential Union quarantine pest.

Physiological Measurements and Transcriptomics Reveal the Fitness Costs of Monochamus saltuarius to Bursaphelenchus xylophilus.

The pine wood nematode (PWN) uses several Monochamus species as vehicles, through a temporary hitchhiking process known as phoresy, enabling it to access new host plant resources. Monochamus saltuarius acts as a new and major vector of the PWN in Northeastern China, showing lower PWN carrying capacity and a shorter transmission cycle compared to established vectors. The apparently altered symbiotic relationship offers an interesting area for researching the costs and adaptions involved in nematode-beetle, a specialized phoresy. We analyzed the response and fitness costs of M. saltuarius through physiological measurements and transcriptomics. The PWN exerted adverse repercussions on the growth and development of M. saltuarius. The PWN accelerated larval development into pupae, while beetle adults carrying the PWN exhibited an elevated abnormality rate and mortality, and reduced starvation resistance. During the pupal stage, the expression of growth-related genes, including ecdysone-inducible genes (E74EA), cuticle proteins, and chitin genes (CHTs), markedly increased. Meanwhile, the induced immune response, mainly by the IMD and Toll signaling pathways, could be a contributing factor to adult abnormality and mortality. Adult gonads and trachea exhibited enrichment in pathways related to fatty acid elongation, biosynthesis, and metabolism. FASN, ELOVL, and SCD possibly contributed to resistance against PWN. Our research indicated that phoretic interactions between vector beetles and PWN vary throughout the vector's lifespan, particularly before and after entry into the trachea. This study highlighted the fitness costs of immunity and metabolism on the vector beetle, indicating the adaptation mechanisms and evolutionary trade-offs to PWN.

Assessing effect of Trichoderma asperellum T16 on management of Bursaphelenchus xylophilus

Pine wilt disease caused by Bursaphelenchus xylophilus is an extremely serious issue worldwide. Trichoderma asperellum is used as a biocontrol agent due to its efficient inhibition of various pathogens. Three solvents, methanol, petroleum ether, and acetone, were used for extracting the fermentation broth of T. asperellum. All three extracts displayed a significant difference in nematocidal efficacy of more than 70% at 72 hours. Water-soluble natural products or polyphenolic compounds exhibited the greatest nematocidal ability after 24 hours of treatment with methanol. However, lipophilic substances exhibit long-lasting nematocidal ability. During this process, the antioxidant enzyme activities of T. asperellum significantly increased, including those of catalase, superoxide dismutase, and peroxidase. The interaction between T. asperellum and B. xylophilus induces the synthesis of glycoside hydrolase family 18 (chitinases) and peptidase S8, potential subtilisin, which dissolve the body wall of the nematodes. Fatty acid metabolism was significantly increased, and a defensive response against substances secreted by the nematode was produced. Antioxidant reaction mechanisms and detoxification metabolism were enriched and included a large number of upregulated DEGs, including GST, CYP450, LysM, and RTA1. The dual and toxic mechanisms exhibited by T. asperellum during its response to B. xylophilus involve multiple pathways and genes that are collectively regulated. This is the first study to investigate the effects of T. asperellum on B. xylophilus. This study provides a theoretical basis for the potential use of T. asperellum as a biocontrol agent against B. xylophilus.

Infestation of pine seedlings (Pinus thunbergii Parl.) with pine wood nematode, Bursaphelenchus xylophilus (Nematoda: Aphelenchoididae) through needle leaves

In order to determine whether the pine wood nematode (PWN), Bursaphelenchus xylophilus can be transmitted into the pine twigs through the needles, and to identify the transmission characteristics, inoculation experiments were conducted on intact pine seedlings and detached pine needles. The experimental results indicate that PWNs could infest pine needles through wounds. Resin ducts distributed in the pine needles were the route for PWN movement. The fastest movement speed of PWN through pine needles was 2.0 cm/h, with an average fastest speed of 0.92 cm/h. PWNs could be transmitted into pine twigs within 12 h of being inoculated onto attached pine needles, ultimately leading to fatal pine wilt disease. This is the first report of PWN infestation and the induction of pine wilt disease through pine needles. After PWN infected pine needles, not all of them entered the twigs, with some nematodes colonized in the needles, where they reproduced.

Bifurcation analysis of pine wilt disease model with both memory-based diffusion and nonlocal effect

Bifurcation analysis of pine wilt disease model with both memory-based diffusion and nonlocal effect