Transmission of Bursaphelenchus xylophilus between Monochamus alternatus and Monochamus saltuarius through interspecific mating behaviour

Cerambycid adults of the genus Monochamus transmit the pine wood nematode (Bursaphelenchus xylophilus [Steiner et Buhrer] Nickle), the causative agent of pine wilt disease. To confirm the transmission of B. xylophilus between vector species, nematode‐infected Monochamus alternatus Hope and nematode‐free Monochamus saltuarius (Gebler) adults were paired and their behaviour was observed for 107–220 min. In three pairs that exhibited mounting without copulation, nematode transmission occurred, whereas it was not found in another pair without mountings. The effect of nematode transmission between different vector species on the invasion biology of B. xylophilus is discussed.     

β-Myrcene,a Potent Attractant Component of Pine Wood for the Pine Wood Nematode,Bursaphelenchus xylophilus

A new convenient assay method for nematode attractants was developed. Using this method, the attracting activity of volatile components in a pine, Pinus densiflora, was examined for the pine wood nematode, Bur saphelenchus xylophilus, which causes serious damage to pine trees in Japan. Among the volatile components, β-myrcene showed the strongest attracting potency. This compound was assumed to play an important role in the transmigration of the nematode from the sawyer to the pine tree and for the movement of the nematode inside the pine wood.     

A new parasitoid (Hymenoptera: Braconidae) of <Emphasis Type="Italic">Monochamus alternatus</Emphasis> (Coleoptera: Cerambycidae) in China

Bracomorpha ninghais sp. n. (Hymenoptera: Braconidae) is described and illustrated based on individuals reared from the immature stages of the pine sawyer Monochamus alternatus (Coleoptera: Cerambycidae) in Zhejiang of China, which is considered a notorious forest pest associated with the main vector of the pine wood nematode Bursaphelenchus xylophilus (Nematoda: Aphelenchoididae) in China.     

On the Taxonomy and Morphology of the Pine Wood Nematode, Bursaphelenchus xylophilus (Steiner &Buhrer 1934) Nickle 1970

During the past 3 yr, nematologists in the United States have found specimens of Bursaphelenchus sp. in the wood of dead and dying pine trees. This nematode-host association resembles a similar interaction reported from Japan where pine trees are being killed by the pine wood nematode. This taxonomic research was conducted to determine if the Japanese pine wood nematode and similar populations in the United States are of the same species. Based upon typical morphological characters of original specimens of Bursaphelenchus xylophilus (Steiner and Buhrer 1934) Nickle 1970 that were rediscovered in the USDA Nematode Collection and genetic crosses among the Japanese and American nematode populations, it was concluded that they are all the same species, B. xylophilus.     

Geographical variation in seasonality and life history of pine sawyer beetles Monochamus spp: its relationship with phoresy by the pinewood nematode Bursaphelenchus xylophilus

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Water relations, xylem embolism and histological features of Pinus thunbergii inoculated with virulent or avirulent pine wood nematode, Bursaphelenchus xylophilus

The development process of pine wilt disease caused by Bursaphelenchusxylophilus (Steiner and Buhrer) Nickle, pine wood nematode,was studied ecophysiologically and histologically in relationto pathogenicity of B. xylophilus. Judging from the predawnxylem pressure potential of needles, the heat pulse velocity,and the soil water potential, the control Pinus thunbergii Parl.,used for the study, was not water-stressed. Virulent B. xylophilusisolate can kill non-waterstressed pines. In virulent B. xylophilusisolateinoculated pines, the predawn xylem pressure potentialof needles abruptly decreased when the colour of 1-year-oldneedles changed to brown and then the water conducting functionof the xylem was lost completely. Avirulent B. xylophilus isolatedoes not affect the needle colour and the xylem pressure potentialof pines. Avirulent B. xylophilus isolate-inoculated pines,however, responded to nematode invasion by decreasing hydraulicconductance of stem and root xylems. In addition, oleoresinexudation slightly decreased. The decreased hydraulic conductanceresults from embolism of tracheids caused by cavitation in thecentral part of the xylem. From histological observation, allof the parenchyma cells in virulent B. xylophilus isolateinoculatedpines died. In contrast, the parenchyma cells, degenerated inavirulent B. xylophilus isolateinoculated pines, were limitedin the embolized region of the xylem. The difference betweenthe response of pine to the virulent B. xylophilus isolate invasionand that to avirulent B. xylophilus isolate invasion indicatesthat nematode-induced death of pine relates to the death ofparenchyma cells, as well as the decrease in xylem hydraulicconductance. Key words: Embolism, hydraulic conductance, parenchyma cells, pathogenicity of pine wood nematode, pine wilt disease.     

用于高灵敏可视化检测松材线虫的闭管等温扩增法

建立了一种基于环介导等温核酸扩增技术(LAMP)的松材线虫高灵敏可视化闭管检测方法。针对松材线虫核糖体DNA的序列保守区域设计LAMP引物,通过优化LAMP体系中的Mg2+、甜菜碱浓度和反应温度等因素,建立了环介导等温扩增法;并结合蜡封反应管对产物进行检测,检测结果可直接通过肉眼观察SYBR Green I荧光显色进行判定。结果表明,本方法可检测到低至10拷贝/管的松材线虫核酸片段,可对单条线虫进行检测,并且具有很高的特异性,能区分检测松材线虫与拟松材线虫。由于整个反应恒温进行,无需热循环仪;闭管检测极大地降低了扩增产物交叉污染的风险;检测速度快,整个检测过程只需40 min,为松材线虫的现场快速筛检提供了一种简便、高灵敏、高特异的工具。     

Newly Discovered Transmission Pathway of Bursaphelenchus xylophilus from Males of the Beetle Monochamus alternatus to Pinus densiflora Trees via Oviposition Wounds

The transmission of Bursaphelenchus xylophilus from Monochamus alternatus males to Pinus densiflora trees via oviposition wounds has been determined. Nematode-infested males, with mandibles fixed experimentally to prevent feeding, were placed for 48 hours with pine bolts containing oviposition wounds that had been made by nematode-free females. After removal of the nematode-infested males, the pine bolts were held for 1 month and then examined for the presence of nematodes. Reproducing nematode populations were recovered from pine bolts that were exposed to male beetles carrying a high number of nematodes. No reproducing nematode population could be recovered from pine bolts exposed to beetles with a small number of nematodes. Nematode reproduction in the pine bolts was not related to the number of oviposition wounds per bolt. Fourth-stage dispersal B. xylophilus juveniles, collected from beetle body surfaces, were inoculated on pine bolt bark 0, 5, 10, and 15 cm away from a single artificial, small hole. These dauer juveniles successfully entered some bolts. The probability of successful nematode reproduction decreased with increased distance between inoculation point and artificial hole. The results indicated that B. xylophilus can move a significant distance to oviposition wounds along the bark surface and enter a tree via the wounds. The new transmission pathway is considered important for the nematode to persist in pine forests such as in North America where pine wilt disease does not occur.     

Carbohydrate Concentration in Pine as Affected by Inoculation with Bursaphelenchus xylophilus

Pines responded to inoculation with Bursaphelenchus xylophilus by changes in reducing and nonreducing carbohydrate concentrations dependent on the pine species and the pathotype of B. xylophilus with which the trees were inoculated. Carbohydrate concentrations, in compatible pine-nematode pathotype combinations, decreased initially after inoculation and then increased slightly before decreasing to approximately 10% of the control levels as the seedlings wilted. In compatible nematode pathotype-pine species combinations, carbohydrate concentrations decreased and then increased as the nematode population densities declined.     

植物根际益生细菌代表性菌株贝莱斯芽孢杆菌FZB42对松材线虫的抑杀性

[目的]由松材线虫导致的松树萎蔫病是松树的毁灭性病害,也是我国最主要的林业病害之一.本研究测评了在农业上广泛使用的、我国微生物肥料行业主要菌种资源之一——贝莱斯芽孢杆菌,对松材线虫的潜在抑杀性能.[方法]选用贝莱斯芽孢杆菌的代表性菌株FZB42为材料,测定对不同条件下的菌液上清、不同菌株的菌液上清、细菌素plantaz...     

Spread of the pinewood nematode vectored by the Japanese pine sawyer: modeling and analytical approaches

The pinewood nematode, Bursaphelenchus xylophilus, is the causative agent of pine wilt of Pinus thunbergii and P. densiflora in Japan. The nematode is vectored by cerambycid beetles of the genus Monochamus. It is inferred to have been introduced from North America early in the 1900s and then to have distributed in China, Korea, and Taiwan. Intensive and/or long-term studies of pine wilt systems have elucidated the pattern and mechanism of the nematode’s spread within a pine stand, dispersal of vector beetles, and spread pattern of pine wilt within a prefecture. The modeling of nematode spread over pine stands, which involves beetle reproduction within a pine stand, has been developing and should elucidate the factors influencing the rate at which the nematode range expands. In this review, we summarize the biologies of the nematode, beetle, and tree, and then characterize the spread of the nematode within a pine stand, locally over pine stands, and regionally over unit administrative districts. Local and regional spreading of the nematode is related primarily to long-distance dispersal by insect vectors and to the artificial transportation of pine logs infested with the nematode and its vector, respectively.     

Competitive displacement of the native species <Emphasis Type="Italic">Bursaphelenchus mucronatus</Emphasis> by an alien species <Emphasis Type="Italic">Bursaphelenchus xylophilus</Emphasis> (Nematoda: Aphelenchida: Aphelenchoididae): a case of successful invasion

The presence of alien invasive species has serious negative impact on endemic biodiversity, especially on native species that occupy the same niche in the ecosystem. To study the influence of the alien invasive species Bursaphelenchus xylophilus on its native sister species B. mucronatus, the two nematode species were mix-cultured in a fungal mat and mix-inoculated into a susceptible host. By comparing the propagation parameters of both species under competitive and noncompetitive conditions it was shown that the propagation level of B. xylophilus was clearly higher than that of B. mucronatus under laboratory culture. Furthermore, the propagation capacity of B. xylophilus under competitive conditions was much higher than that under noncompetitive conditions, both in laboratory culture and with host inoculation. Bursaphelenchus xylophilus also excluded B. mucronatus when the two species were cultured as a mixture for a longer time. The relative abundance ratios of the two species in natural pinewoods were also determined by random sampling of dying pine trees from regions with different invasion histories. It was noted that with an increase in invasion years the distribution frequency of B. xylophilus increased while that of B. mucronatus decreased. Experimental tests verified our hypothesis that because of its high fecundity and strong competitive ability, the invasive species B. xylophilus out-competed the native species B. mucronatus and displaced it in natural ecosystems. The successful invasion of B. xylophilus is attributed to competitive displacement, which may be one of the ecological invasive mechanisms.     

Cloning and characterization of an extracellular serine protease from the nematode-trapping fungus <Emphasis Type="Italic">Arthrobotrys conoides</Emphasis>

An extracellular serine protease (Ac1) with a molecular mass of 35 kDa was purified from the nematode-trapping fungus Arthrobotrys conoides. The optimum activity of Ac1 is at pH 7.0 and 53.2°C (over 20 min). Ac1 can degrade a broad range of substrates including casein, gelatin, bovine serum albumin, collagen, and nematode cuticles. Moreover, the enzyme can immobilize the free-living nematode Panagrellus redivivus and the pine wood nematode Bursaphelenchus xylophilus, indicating Ac1 may be involved in infection against nematodes. The encoding gene of Ac1 contains one intron of 60-bp and two exons encoding a polypeptide of 411 amino acid residues. The deduced polypeptide sequence of Ac1 showed a high degree of similarity to two previously reported serine proteases PII and Mlx from other nematode-trapping fungi (81% aa sequence identity). However, three proteases Ac1, Aoz1 and Mlx showed optimum temperatures at 53.2, 45 and 65°C, respectively. Compared to PII, Ac1 appears to have a significantly higher activity against gelatin, bovine serum albumin, and non-denatured collagen. Moreover, our bioassay experiments showed that Ac1 is more effective at immobilizing P. redivivus than B. xylophilus.     

Physiology and Molecular Characteristics of a Pine Wilt Nematode-Trapping Fungus, <Emphasis Type="Italic">Monacrosporium megalosporum</Emphasis>

We isolated the nematode-trapping fungus Monacrosporium megalosporum from nature and examined its morphology, physiology and molecular characteristics. The nematode-trapping device of this fungus is a three-dimensional network. This fungus captures the pine wilt nematode (Bursaphelenchus xylophilus), but not a non-phytopathogenic nematode that is morphologically similar to B. xylophilus. The phylogenic relationship of the nucleotide sequence of the rDNA ITS region was close to those of M. thaumasium and Geniculifera eudermata, which also have nematode-trapping devices that are three-dimensional networks. Acidic pH inhibited both the liberation and regeneration of protoplasts. Moreover, cytoplasmic granulation of protoplasts was found below pH 6.0. Mycelial growth on agar media was also inhibited below pH 4, but not at pH 9. These results strongly suggest that the activity of this fungus is inhibited by acid rain in the field. Therefore, development of pine wilt disease might be a secondary effect of acid rain.     

A Nondestructive Method of Determining Bursaphelenchus xylophilus Infestation of Monochamus spp. Vectors

Pine wilt is caused by the nematode Bursaphelenchus xylophilus, which is transported to host trees in the trachea of Monochamus spp. (Coleoptera: Cerambycidae). The study of the relationship between the nematode and its beetle vectors has been hampered by the inability to estimate nematode presence or density within live beetles. This report describes a rapid method for estimating nematode load within live M. carolinensis and M. alternatus by visual examination of the atrium of the first abdominal spiracle. Visual estimates of nematode numbers correlated highly with actual nematode numbers. This method is a timesaving technique for determining relative numbers of B. xylophilus in pine wilt research.     

Pathogenicity of Bursaphelenchus xylophilus on Pines in Minnesota and Wisconsin

The pinewood nematode, Bursaphelenchus xylophilus, was inoculated into established native jack and red pines (Pinus banksiana and P. resinosa) and exotic Austrian pine (P. nigra) in Minnesota and Wisconsin forests during summer 1981. The nematode isolates did not kill established nonstressed pine trees growing in the forest. However, the same nematode isolates killed pine seedlings under greenhouse conditions. Girdling the main stem of some trees to induce stress resulted in the death of the majority of inoculated and noninoculated branches of Austrian and jack pines, but no branch death was observed on red pine. Greater numbers of nematodes were extracted from branches of inoculated, girdled trees than from nongirdled trees. The mean number of nematodes extracted from branches of inoculated, nongirdled trees was 0.3 - 14 nematodes per gram of wood.     

Top 10 plant‐parasitic nematodes in molecular plant pathology

The aim of this review was to undertake a survey of researchers working with plant‐parasitic nematodes in order to determine a ‘top 10’ list of these pathogens based on scientific and economic importance. Any such list will not be definitive as economic importance will vary depending on the region of the world in which a researcher is based. However, care was taken to include researchers from as many parts of the world as possible when carrying out the survey. The top 10 list emerging from the survey is composed of: (1) root‐knot nematodes (Meloidogyne spp.); (2) cyst nematodes (Heterodera and Globodera spp.); (3) root lesion nematodes (Pratylenchus spp.); (4) the burrowing nematode Radopholus similis; (5) Ditylenchus dipsaci; (6) the pine wilt nematode Bursaphelenchus xylophilus; (7) the reniform nematode Rotylenchulus reniformis; (8) Xiphinema index (the only virus vector nematode to make the list); (9) Nacobbus aberrans; and (10) Aphelenchoides besseyi. The biology of each nematode (or nematode group) is reviewed briefly.