Pine Wood Nematode Bursaphelenchus Xylophilus Research Articles

Identification and Validation of Reference Genes for Gene Expression Analysis in Monochamus saltuarius Under Bursaphelenchus xylophilus Treatment.

A special mutual relationship exists between the pine wood nematode (PWN) Bursaphelenchus xylophilus and its vector beetles of genus Monochamus, which enables PWN to spread, at the same time provides longhorned beetles with more weak hosts. PWN are attracted to the pupal chambers and then carried inside the trachea of beetle adults, which is a necessary part to complete the B. xylophilus infection cycle. The growth and immune responses of the vector beetle will affect this carrying process, however, they were rarely studied in Monochamus saltuarius. Real-time quantitative polymerase chain reaction (RT-qPCR), one of the most common methods for quantitative gene expression analysis, was performed to explore the key genes and pathways involved in the growth, development and immune responses of M. saltuarius at different developmental stages associated with infection of PWN and PWN treatment conditions. To enhance the accuracy of RT-qPCR data, the expression of target genes needs to be normalized with reference genes, which are stably expressed under varied experimental conditions. In our study, the stability of 14 candidate reference genes in M. saltuarius samples at different developmental stages associated with infection of PWN or PWN treatment conditions was evaluated using delta Ct, geNorm, NormFinder, BestKeeper and RefFinder algorithms. Moreover, KLF gene was used to validate the stability of the selected reference genes. Under experimental conditions of this study, RPL7 and TER were suitable reference genes at different developmental stages associated with infection of PWN. RPL7 and RPS5 were considered the most stable reference genes in the pupae treated with PWN. RPS5 and SNX6 could be used as reference genes in the adults treated with PWN. RPL7, EF1-γ, and RPS5 could be used as stable reference genes in all the samples. This work is the first to evaluate reference genes in M. saltuarius, laying a foundation for further gene expression experimental procedures and understanding the phoretic relationship between M. saltuarius and B. xylophilus.

Transcriptome profiling and RNA interference reveals relevant detoxification genes in Monochamus alternatus response to (+)‐α‐pinene

AbstractUnderstanding the mechanism of insect resistance to toxic effects of phytochemicals can provide an insight into plant–herbivore interactions. Monochamus alternatus Hope, a main vector of pine wood nematode (Bursaphelenchus xylophilus), prefers to infest masson pine (Pinus massoniana Lamb) and causes huge economic and environmental losses. α‐Pinene is the primary component of resin produced by masson pine and plays a crucial role in defending against herbivorous insects, but its defensive effects on M. alternatus larvae are barely known. Here, we explored the physiological metabolism in M. alternatus larvae that were fumigated with (+)‐α‐pinene, (‐)‐α‐pinene, β‐pinene, (R)‐(+)‐limonene, myrcene and (‐)‐α‐phellandrene. (+)‐α‐Pinene showed the highest fumigant toxicity to M. alternatus larvae among these monoterpenes, and the fourth instar larvae possessed the highest resistance to this compound at the larval stage. Comparative transcriptome analysis detected 423 up‐regulated and 311 down‐regulated genes in the larvae fumigated with (+)‐α‐pinene, which were mainly related to detoxification, energy and protein metabolism. Among the differentially expressed genes encoding for detoxification enzymes, 14 P450s, 13 UGTs, 1GSTs and 3ABCs were dramatically up‐regulated in the larvae fumigated with (+)‐α‐pinene. Silencing of P450s via RNA interference led to an increased mortality in the larval fumigated with (+)‐α‐pinene. Piperonyl butoxide exposure significantly increased the mortality and inhibited the expressions of P450s, UGTs and ABCs in the larvae fumigated with (+)‐α‐pinene. These results suggested an important role of P450s in the resistance of M. alternatus larvae to (+)‐α‐pinene fumigation, which may facilitate the understanding of terpenoid detoxification in M. alternatus larvae.

Phenolic Compounds Regulating the Susceptibility of Adult Pine Species to Bursaphelenchus xylophilus

Pine wilt disease (PWD), caused by the pinewood nematode (PWN) Bursaphelenchus xylophilus, is one of the most destructive diseases in trees of the genus Pinus and is responsible for significant environmental and economic losses in North America, Eastern Asia, and Western Europe. However, pine species are not equally affected, with some being tolerant/resistant while others are susceptible to nematode infection for reasons still unclear. The present study aims to investigate differential chemical responses of susceptible and tolerant/resistant pine species shortly after nematode infection by characterizing the phenolic profiles of adult Pinus sylvestris, Pinus pinaster, Pinus pinea, and Pinus halepensis. HPLC and LC-MS were used to identify and quantify the pine´s phenolic compounds: gallic acid, ferulic acid, taxifolin, rutin, resveratrol, (+)-secoisolariciresinol, (−)-epicatechin, protocatechuic acid hexoside, gallic acid hexoside, ferulic acid glucoside, quercetin hexoside, and two unidentified compounds (#A and #B). Prior to infection, we could not differentiate between nematode-tolerant/resistant and susceptible adult pine species based on their constitutive phenolic compounds. In the presence of the PWN, the phenolic profile allowed for a noticeable separation of the PWN-tolerant/resistant P. halepensis from the susceptible P. sylvestris, contrasting with a more homogenous response from P. pinea and P. pinaster. Observations on P. halepensis suggest that taxifolin, resveratrol, and rutin may have an active role in protecting against B. xylophilus, possibly in conjugation with other biochemical and anatomical characters. We emphasize the importance of studying pine tolerant/resistance on adult trees, and not on excised branches, saplings, or seedlings to accurately simulate the nematode–pine host interactions occurring under natural conditions.

Expression of the Thaumatin-Like Protein-1 Gene (Bx-tlp-1) from Pine Wood Nematode Bursaphelenchus xylophilus Affects Terpene Metabolism in Pine Trees.

Pine wilt disease is a major forest disease worldwide, including in China, where it has severely damaged pine forest ecosystems, and the pathogen is pine wood nematode (Bursaphelenchus xylophilus). The thaumatin-like protein-1 gene (Bx-tlp-1) is a key gene associated with B. xylophilus pathogenicity, which is also responsive to α-pinene. In this study, an examination of Pinus massoniana seedlings infected by B. xylophilus revealed that monoterpene (sesquiterpene) levels peaked on days 15 and 27 (days 18 and 27). Meanwhile, P. massoniana Pm-tlp expression levels were high on days 3, 12, and 27, which were consistent with the expression of key enzymes genes in the terpene biosynthesis pathway. The functional similarity of B. xylophilus Bx-TLP-1 and P. massoniana Pm-TLP suggests Bx-TLP-1 and Pm-TLP may have similar roles in P. massoniana. There was also no secondary accumulation of terpenes in P. massoniana seedlings during B. xylophilus treated with dsRNA targeting Bx-tlp-1 (dsTLP1) infections, reflecting the decreased pathogenicity of B. xylophilus and the delayed disease progression in pine trees. And the results of micro-CT showed that the degree of cavitation for the trees inoculated with Bx-TLP-1 (0.3811 mm3) was greater than that for the trees inoculated with dsTLP1 PWNs (0.1204 mm3) on day 15 after inoculation. Results from this study indicated that B. xylophilus Bx-tlp-1 gene may induce the upregulated expression of related genes encoding enzymes in the terpene synthesis pathway of P. massoniana, resulting in the accumulation of terpenes, which also provided an insight to investigate the B. xylophilus pathogenicity in the future.

Bacterial Diversity and Pathogenicity of Pine Wood Nematode (Bursaphelenchus xylophilus) from Two Diff erent Sources

Pine wilt disease is a devastating disease of pine trees caused by a pine wood nematode (PWN), Bursaphelenchus xylophilus (Steiner & Buhrer) Nickle. We studied the bacteria carried by B. xylophilus from Fushan Mountain and Qingdao University Campus (F and Q samples) and the pathogenicity of the two PWN samples to explore the relationship between PWN companion bacteria and its pathogenicity. Based on metagenomic analysis, the distribution of the bacteria from the two samples was signifi cantly different. At the phylum level, Proteobacteria is the largest phylum in the two samples, 85 and 65% in F and Q samples, respectively. At the family level, Enterobacteriaceae and Rhizobiaceae were dominant in F sample with the total relative abundance of 55% while the two bacterial families only accounted for 15% in Q sample. Moreover, Burkholderiaceae was only detected in F sample. PICRUSt analysis based on KEGG database showed that the bacteria carried by B. xylophilus from F sample had stronger metabolic abilities. In addition, BugBase analysis predicted that the bacteria from F sample had stronger effect on pathogenicity and antioxidant stress. Furthermore, we tested the feeding ability and pathogenicity of F and Q samples, and found that the B. xylophilus of F sample had stronger feeding ability and pathogenicity, which was consistent with the results of PICRUSt analysis based on KEGG database and BugBase analysis. Our research indicated that the pathogenicity of B. xylophilus could be closely related to the vitality of its associated bacteria, and Enterobacteriaceae, Rhizobiaceae and Burkholderiaceae belonging to Proteobacteria phylum were important pathogenicity-related bacterial families, which is valuable for the study on the pathogenesis of B. xylophilus.

Identification of Olfactory Genes in Monochamus saltuarius and Effects of Bursaphelenchus xylophilus Infestation on Their Expression

The pine wood nematode (PWN) Bursaphelenchus xylophilus has caused disastrous losses of pine forests in many countries, and the success of PWN depends strongly on interactions with its insect vectors. Monochamus saltuarius is a newly recorded vector in Northeast China. Feeding (i.e., immature) and egg-laying (i.e., mature) Monochamus spp. target different host plants, and olfactory cues play important roles regarding host choice. Whether infestation with PWN affects olfactory mechanisms in M. saltuarius related to feeding and oviposition is of interest as this may affect the spread of nematodes to new healthy hosts. However, little is known about molecular mechanisms of the olfactory system of M. saltuarius. We identified chemosensory-related genes in adult M. saltuarius and examined the influence of B. xylophilus on the respective expression patterns. Fifty-three odorant-binding proteins (OBPs), 15 chemosensory proteins, 15 olfactory receptors (ORs), 10 gustatory receptors, 22 ionotropic receptors (IRs), and two sensory neuron membrane proteins were identified, and sex bias among non-infested beetles was mainly found with respect to expression of OBPs. Interestingly, OBPs and ORs were markedly down-regulated in male M. saltuarius infested with B. xylophilus, which may reduce olfactory sensitivity of male M. saltuarius and affect the spreading of B. xylophilus to new hosts. Our results will help understand the interactions between B. xylophilus and M. saltuarius, which may lead to the identification of new control targets in the olfactory system of M. saltuarius.

Bacillus thuringiensis toxins with nematocidal activity against the pinewood nematode Bursaphelenchus xylophilus

The pine wilt disease is caused by the pinewood nematode Bursaphelenchus xylophilus and it results in serious ecological and economic losses. Therefore, effective prevention and control methods for the pinewood nematode are urgently required. Bacillus thuringiensis (Bt), a widely used microbial insecticide, produces toxins that are toxic to several species of parasitic nematodes, however, its effects on B. xylophilus have not been determined. In this study, Cry5Ba3, App6Aa2, Cry12Aa1, Cry13Aa1, Cry14Aa1, Cry21Aa3, Cry21Fa1, Xpp55Aa1, and Cyt8Aa1 toxins’ nematocidal activity against B. xylophilus was evaluated, six toxins with high toxicity were identified: App6Aa2 (LC50 = 49.71 μg/mL), Cry13Aa1 (LC50 = 53.17 μg/mL), Cry12Aa1 (LC50 = 58.88 μg/mL), Cry5Ba3 (LC50 = 63.99 μg/mL), Xpp55Aa1 (LC50 = 65.14 μg/mL), and Cyt8Aa1 (LC50 = 96.50 μg/mL). The six toxins caused shrinkage and thinning of the intestinal cells, contraction of the intestine from the body wall, vacuolization, and degenerated appearance of the pinewood nematodes. The results of this study provide basic information to study the action mechanism of nematocidal toxins on the pinewood nematode and direction for the use of nematocidal toxins in the biological control of B. xylophilus.

Efficient dead pine tree detecting method in the Forest damaged by pine wood nematode (Bursaphelenchus xylophilus) through utilizing unmanned aerial vehicles and deep learning-based object detection techniques

Pine wood nematode (Bursaphelenchus xylophilus) is an invasive pathogen in South Korea, where it has caused pine wilt disease (PWD) with extremely high mortality of native pine species (Pinus densiflora, Pinus thunbergii, and Pinus koraiensis). Since the disease spreads by its vectors, native pine sawyer beetles (Monochamus alternatus and Monochamus saltuarius), the cost of monitoring the expansion has been rapidly increasing. Furthermore, it is even more costly to eliminate new and isolated infections since unremoved infected trees act as new sources of infection through the preferred oviposition of the beetles on such trees. The methodology of combining unmanned aerial vehicle (UAV) and object detection based on deep learning provides the opportunity to solve such problems, as UAV with RGB camera can provide high spatial resolution aerial image and digital surface model (DSM), which can be used for object detection with excellent results. In this study, we evaluated the performance of this method to detect dead pine trees in PWD-damaged areas. In particular, to ensure low omission error of monitoring, YOLOv3 was employed for object detection as the model design is focused on minimizing the omission error. We also modified the model so that the positions and crown diameter could be estimated. Four detection models were trained using four different combinations between aerial images (R, G, B) and DSM from UAV. Among them, the model from RGB showed the highest performance (recall: 0.9909, precision: 0.8438) and was selected as the optimal model. Our results suggest that our method can contribute to low-cost and effective monitoring of the dead pine trees while maintaining low omission error, which is critical for PWD management.

Surveillance of pine wilt disease by high resolution satellite

Pine wilt disease caused by the pinewood nematode Bursaphelenchus xylophilus has led to the death of a large number of pine trees in China. This destructive disease has the characteristics of bring wide-spread, fast onset, and long incubation time. Most importantly, in China, the fatality rate in pines is as high as 100%. The key to reducing this mortality is how to quickly find the infected trees. We proposed a method of automatically identifying infected trees by a convolution neural network and bounding box tool. This method rapidly locates the infected area by classifying and recognizing remote sensing images obtained by high resolution earth observation Satellite. The recognition accuracy of the test data set was 99.4%, and the remote sensing image combined with convolution neural network algorithm can identify and determine the distribution of the infected trees. It can provide strong technical support for the prevention and control of pine wilt disease.

MPs, insects and trees: The Pine Wood Nematode in the Portuguese Parliament

The Pine Wood Nematode (PWN) Bursaphelenchus xylophilus is the causal agent of the pine wilt disease, and a quarantine organism within the European Union. This pathogen was first detected in Portugal in 1999, associated to dead coastal pines (Pinus pinaster), its vector among trees being the native insect Monochamus galloprovincialis. Over the years, the management and control of both the nematode and the vector has been implemented by the Portuguese National Programme to Control the Pine Wood Nematode (PROLUNP), one of whose main current strategies is focused on the prevention of dispersal of wilt disease to new locations. This paper aims to explore how the pathogen and the forestry management strategy were perceived by the members of the parliament (MPs) of the Portuguese Republic, based on documents from 1999 until the present day.

Effect of Bursaphelenchus spp. inoculation on carbohydrate concentrations of differentpine species in forest stands of Düzce Forest Directorate

The pinewood nematode (Bursaphelenchus xylophilus) is one of the most important pathogens of conifer forests worldwide that causes the pine wilt disease. This problem has increased the scientific interest in Bursaphelenchus species both in the world and in Turkey. Previously, six Bursaphelenchus species were isolated from wilted pine trees in Turkey. The main goal of this study was to investigate the effects of nematode inoculation on the total carbohydrate concentrations of tree species. Native six Bursaphelenchus species were inoculated on three pine species (Pinus pinaster, P. nigra, and P. sylvestris) under natural stand conditions. Two different doses of nematodes (2000 and 20,000) were used for inoculation. For each treatment, three trees of each species were inoculated. The total carbohydrate concentrations were differed significantly among tree species, nematode species and between nematode doses. The total carbohydrate concentration values were higher in P. pinaster than both P. nigra and P. sylvestris. These results may suggest that pine species responded to nematode inoculation by changing the amount of TCC.

Obtaining and Maintaining Cultures of Pinewood Nematodes Bursaphelenchus xylophilus from Wild Dauers.

The establishment of laboratory isolates of the pinewood nematode Bursaphelenchus xylophilus, the causal agent of the pine wilt disease, has been crucial to research on this important forest pathogen. Here we describe a simple, low-cost, and easy way to obtain samples of wild populations of B. xylophilus by culturing dauers extracted directly from the insect vector.

Inference of the worldwide invasion routes of the pinewood nematode Bursaphelenchus xylophilus using approximate Bayesian computation analysis

Population genetics have been greatly beneficial to improve knowledge about biological invasions. Model-based genetic inference methods, such as approximate Bayesian computation (ABC), have brought this improvement to a higher level and are now essential tools to decipher the invasion routes of any invasive species. In this paper, we performed ABC analyses to shed light on the pinewood nematode (PWN) worldwide invasion routes and to identify the source of European populations. Originating from North America, this microscopic worm has been invading Asia since 1905 and Europe since 1999, causing tremendous damage on pine forests. Using microsatellite data, we demonstrated the existence of multiple introduction events in Japan (one involving individuals originating from the USA and one involving individuals with an unknown origin) and China (one involving individuals originating from the USA and one involving individuals originating from Japan). We also found that Portuguese samples had an American origin. Although we observed some discrepancies between descriptive genetic methods and the ABC method, which are worth investigating and are discussed here, the ABC approach definitely helped clarify the worldwide history of the PWN invasion.

Could Pine Wood Nematode (Bursaphelenchus xylophilus) Cause Pine Wilt Disease or Even Establish inside Healthy Trees in Finland Now—Or Ever?

Pine wilt disease (PWD) caused by the pine wood nematode (PWN, Bursaphelenchus xylophilus) can, in suitable conditions, lead to mass mortality of susceptible trees. In the European Union, PWN is a quarantine pest. To support PWN risk management in Finland, we assessed the suitability of the Finnish present and future climate for both PWD and PWN establishment inside susceptible healthy trees. The former was done using the mean summer temperature concept and the latter by relating annual growing degree days to the likelihoods of PWN extinction and establishment inside healthy trees. The likelihoods were derived from the previously published modelling of PWN population dynamics for 139 locations in Germany. Both assessments were conducted using 10 × 10 km resolution climate data from 2000–2019 and Finland-specific climate change projections for 2030–2080. The results indicate that the present Finnish climate is too cool for both PWD and PWN establishment inside healthy trees. Furthermore, even global warming does not appear to turn the Finnish climate suitable for PWD or PWN establishment inside healthy trees by 2080, except under the worst-case representative concentration pathway scenario (RCP8.5). Consequently, giving top priority to PWN when allocating resources for biosecurity activities in Finland might deserve reconsideration.

Phytochemicals as Biopesticides against the Pinewood Nematode Bursaphelenchus xylophilus: A Review on Essential Oils and Their Volatiles.

The impacts of a rapidly changing environment together with the growth in global trade activities has promoted new plant pest pandemic events in forest ecosystems. The pinewood nematode (PWN), Bursaphelenchus xylophilus, causes strong worldwide economic and ecological impacts. Direct control is performed through trunk injection of powerful nematicides, however many of these (hemi)synthetic compounds have raised ecological and human health concerns for affecting non-target species and accumulating in food products. As sustainable alternatives, essential oils (EOs) have shown very promising results. In this work, available literature on the direct activity of EOs against PWN is reviewed, as a contribution to advance the search for safer and greener biopesticides to be used in sustainable PWD pest management strategies. For the first time, important parameters concerning the bioassays performed, the PWNs bioassayed, and the EOs used are summarized and comparatively analyzed. Ultimately, an overview of the chemical composition of the most active EOs allowed to uncover preliminary guidelines for anti-PWN EO efficiency. The analysis of important information on the volatile phytochemicals composing nematicidal EOs provides a solid basis to engineer sustainable biopesticides capable of controlling the PWN under an integrated pest management framework and contributes to improved forest health.

Primary Metabolite Adjustments Associated With Pinewood Nematode Resistance in Pinus pinaster.

The pinewood nematode (PWN) Bursaphelenchus xylophilus is the causal agent of the pine wilt disease (PWD) and represents one of the major threats to conifer forests. The detection of the PWN in Portugal, associated with Pinus pinaster, increased the concern of its spread to European forests. Despite its susceptibility to PWD, genetic variability found among P. pinaster populations has been associated with heritable PWD resistance. Understanding the mechanisms underlying tree resistance constitutes a valuable resource for breeding programs toward more resilient forest plantations. This study investigated changes in anatomy, chlorophyll a fluorescence (ChlF), and primary metabolism in susceptible and resistant P. pinaster half-sib plants, after PWN inoculation. Susceptible plants showed a general shutdown of central metabolism, osmolyte accumulation, photosynthetic inhibition, and a decrease in the plant water status. The ChlF transient rise (OJIP curve) revealed the appearance of L- and K-bands, indicators of environmental stress. In contrast, resistant plants revealed a regulated defense response and were able to restrict PWN migration and cellular damage. Furthermore, the accumulation of γ-aminobutyric acid (GABA) and succinate suggested a role of these metabolites in PWD resistance and the possible activation of the GABA shunt. Altogether, these results provide new insights to the role of primary metabolism in PWD resistance and in the selection of resistant phenotypes for disease mitigation.

Optimization of a solid culture medium based on Monochamus alternatus for Cordyceps militaris fruiting body formation.

Monochamus alternatus (Coleoptera: Cerambycidae; M. alternatus), popularly known as the Japanese pine sawyer, is a vector of pinewood nematode (Bursaphelenchus xylophilus) that causes pine wilt disease. A solid medium culture with M. alternatus produced Cordyceps militaris fruiting bodies with the longest strips and the highest biological efficiency. Supplementing the original form of M. alternatus with oats resulted in slightly enhanced fruiting body production. The original form of M. alternatus showed higher production than its powder form. The solid culture medium was optimized using a response surface methodology, and the optimal medium contained the following: 8·5g per bottle of M. alternatus and 11·5g per bottle of oats mixed with 22·4ml of water in a 300-ml cylindrical plastic bottle. The optimal culturing period for the fruiting body formation was 37·1days. Under these conditions, a fruiting body dry weight of 38·0g per bottle (actual value) was attained. The fruiting body produced using a solid culture medium based on M. alternatus had a cordycepin content of about 25µgg-1 . The solid culture medium containing M. alternatus is highly efficient and eco-friendly, and its effectiveness in large-scale fruiting body production from C. militaris has been demonstrated.

Insights into the Role of Fungi in Pine Wilt Disease.

Pine wilt disease (PWD) is a complex disease that severely affects the biodiversity and economy of Eurasian coniferous forests. Three factors are described as the main elements of the disease: the pinewood nematode (PWN) Bursaphelenchus xylophilus, the insect-vector Monochamus spp., and the host tree, mainly Pinus spp. Nonetheless, other microbial interactors have also been considered. The study of mycoflora in PWD dates back the late seventies. Culturomic studies have revealed diverse fungal communities associated with all PWD key players, composed frequently of saprophytic fungi (i.e., Aspergillus, Fusarium, Trichoderma) but also of necrotrophic pathogens associated with bark beetles, such as ophiostomatoid or blue-stain fungi. In particular, the ophiostomatoid fungi often recovered from wilted pine trees or insect pupal chambers/tunnels, are considered crucial for nematode multiplication and distribution in the host tree. Naturally occurring mycoflora, reported as possible biocontrol agents of the nematode, are also discussed in this review. This review discloses the contrasting effects of fungal communities in PWD and highlights promising fungal species as sources of PWD biocontrol in the framework of sustainable pest management actions.

The Virulence of S. marcescens Strains Isolated From Contaminated Blood Products Is Divergent in the C. elegans Infection Model.

Bacterial contamination of platelet concentrates (PCs) can occur during blood donation or PC processing, necessitating routine screening to identify contaminated products in efforts to prevent adverse transfusion reactions in recipient patients. Serratia marcescens is a common bacterial contaminant, and its resilient nature coupled with genetic promiscuity imbue this environmental bacterium with resistance to disinfectants and antibiotics enhancing bacterial virulence. In this study, we aim to understand adaptive survival mechanisms through genetic characterization of two S. marcescens strains, CBS11 and CBS12, isolated from PCs by Canadian Blood Services. Genomic analyses of the two strains indicated that CBS11 has one chromosome and one plasmid (pAM01), whereas CBS12 has no plasmids. Phylogenetic analyses show that CBS11 and CBS12 are non-clonal strains, with CBS11 clustering closely with clinical strain CAV1492 and less so with environmental strain PWN146, and CBS12 clustering with a clinical strain AR_0027. Interestingly, pAM01 was most closely related to PWN146p1, a plasmid found in S. marcescens PWN146 strain associated with pinewood nematode Bursaphelenchus xylophilus. Lastly, the genomic diversity of CBS11 and CBS12 was not reflected in the antibiotic resistance profiles as they were remarkably similar to one another, but was reflected in the virulence phenotypes assessed in the Caenorhabditis elegans nematode infection model, with CBS11 being more virulent then CBS12. Taken together, we suggest that S. marcescens environmental isolates that feature evolutionary diverse genomics are better equipped to adapt and thrive in varied environments, such as that of PCs, and therefore is as much of a concern as multi-drug resistance for human infection potential.

Factors Affecting the Ratio of Female to Male of Pinewood Nematodes Bursaphelenchus xylophilus (Steiner & Buhrer) Nickle

The pinewood nematode Bursaphelenchus xylophilus (B. xylophilus) is responsible for a devastating disease of pine forests. Its pathogenicity is closely related to the numbers of individual B. xylophilus. The ratio of female to male (sex ratio) is key to understanding population change in this species. The sex ratio of B. xylophilus varies widely, but it is unclear how it is affected by environmental changes. The sex ratios of nematodes, isolated from different samples in the wild, varied between 0.93 and 2.20. Under laboratory conditions, maternal age and the population did not affect the sex ratio of progeny. A change from good to poor nutritional status was associated with a reduction of the sex ratio of progeny from 1.85 to 1.41, which was speculated to result from a change in the primary sex ratio. Thus, B. xylophilus effectively maintains the sex ratio with maternal age and population changes but adjusts the sex ratio of progeny on the basis of the changes in nutrition.