Identification and evidence for relationships among geographical isolates of Bursaphelenchus spp. (pinewood nematode) using homologous DNA probes

Subspecific Synonym of Monochamus alternatus (Coleoptera: Cerambycidae): Population Genetics and Morphological Reassessment

Monochamus alternatus Hope, 1842, is a major forest pest that hosts the pathogenic pinewood nematode (PWN), Bursaphelenchus xylophilus (Steiner and Buhrer, 1934) Nickle 1970. Taxonomically, M. alternatus is currently divided into two subspecies, based on morphology and geography: Monochamus alternatus alternatus Hope, 1842 in China, Taiwan, Tibet, Vietnam, and Laos and Monochamus alternatus endai Makihara, 2004 in South Korea and Japan. Despite their economic importance, the subspecies taxonomy of M. alternatus has never been tested after the first description. In this study, we aimed to reassess the subspecies taxonomy of M. alternatus using molecular and morphological data. For morphological analysis, we examined three major morphological characters (pronotal longitudinal band, granulation on humeri, and elytral proximomedial spine) from 191 individuals from China, Korea, and Taiwan. Population genetic structures were examined using 85 de novo sequences and 82 public COI sequences from China, Korea, Japan, Malaysia, Taiwan, and a few intercepted specimens from the United States. All the genetic data were aligned as three different multiple sequence alignments. Individuals from each subspecies were morphologically and genetically scattered, not clustered according to subspecies in any of the analyses. Therefore, a new synonymy is proposed: Monochamus alternatus Hope, 1842 = Monochamus alternatus endai, syn. n. This study suggests a more robust classification of M. alternatus for the first time and ultimately will pose a substantial impact on implementing quarantine or forestry policies.

Transformation of Multi-Antibiotic Resistant Stenotrophomonas maltophilia with GFP Gene to Enable Tracking its Survival on Pine Trees

Pinus massoniana Lamb., commonly known as Masson Pine, is one of the most important tree species for planted forests in China. This species is, however, threatened by pine wilt disease caused by Bursaphelenchus xylophilus. Stenotrophomonas maltophilia (Palleroni & Bradbury 1993) Smal-007, a bacterium isolated from the body surface of native B. xylophilus, was evidenced to possess the ability to prevent and control this disease. In this study, we focus on exploring effective transformation and green fluorescent protein (GFP)-labeling of Smal-007, in order to facilitate its later investigation. The results indicated that the recombination of antibiotic Tp (trimethoprim), and the uncoupling reagent, CCCP (carbonyl cyanide m-chlorophenyl hydrazine), was effective for the transformation of the multidrug-resistant bacterium. An optimal transformation procedure, including electroporation, was established. To the best of our knowledge, this is the first report where such a method was used for S. maltophilia transformation. Furthermore, Smal-007 was labeled by GFP, allowing the monitoring of its survival ability in pine trees. The labeling was robust and recognizable in isolates recovered from pine needles and bark. In summary, our study indicated that combining uncoupling reagents could be a useful approach to finding operative antibiotic markers for the transformation of multidrug-resistant bacteria. In addition, our successful labeling of Smal-007 with GFP could improve the understanding of its ecological impact, when used as a biocontrol agent.

Protein markers of Bursaphelenchus xylophilus Steiner & Buhrer, 1934 (Nickle, 1970) populations using quantitative proteomics and character compatibility

The Pine Wood Nematode (PWN) Bursaphelenchus xylophilus is a severe forest pathogen in countries where it has been introduced and is considered a worldwide quarantine organism. In this study, protein markers for differentiating populations of this nematode were identified by studying differences among four selected Iberian and one American population. These populations were compared by quantitative proteomics (iTRAQ). From a total of 2860 proteins identified using the public database from the B. xylophilus genome project, 216 were unambiguous and significantly differentially regulated in the studied populations. Comparisons of their pairwise ratio were statistically treated and supported in order to convert them into discrete character states, suggesting that 141 proteins were not informative as population specific markers. Application of the Character Compatibility methodology on the remaining 75 proteins (belonging to families with different biological functions) excludes 27 which are incompatible among them. Considering only the compatible proteins, the method selects a subset of 30 specific unique protein markers which allowed the compared classification of the Iberian isolates. This approach makes it easier search for diagnostic tools and phylogenetic inference within species and populations of a pathogen exhibiting a high level of genetic diversity.

First insights into the genetic diversity of the pinewood nematode in its native area using new polymorphic microsatellite loci

The pinewood nematode, Bursaphelenchus xylophilus, native to North America, is the causative agent of pine wilt disease and among the most important invasive forest pests in the East-Asian countries, such as Japan and China. Since 1999, it has been found in Europe in the Iberian Peninsula, where it also causes significant damage. In a previous study, 94 pairs of microsatellite primers have been identified in silico in the pinewood nematode genome. In the present study, specific PCR amplifications and polymorphism tests to validate these loci were performed and 17 microsatellite loci that were suitable for routine analysis of B. xylophilus genetic diversity were selected. The polymorphism of these markers was evaluated on nematodes from four field origins and one laboratory collection strain, all originate from the native area. The number of alleles and the expected heterozygosity varied between 2 and 11 and between 0.039 and 0.777, respectively. First insights into the population genetic structure of B. xylophilus were obtained using clustering and multivariate methods on the genotypes obtained from the field samples. The results showed that the pinewood nematode genetic diversity is spatially structured at the scale of the pine tree and probably at larger scales. The role of dispersal by the insect vector versus human activities in shaping this structure is discussed.

Genetic variation in the invasive process of Bursaphelenchus xylophilus (Aphelenchida: Aphelenchoididae) and its possible spread routes in China

Pinewood nematode (Bursaphelenchus xylophilus) is an invasive species that causes a destructive forest disease-pine wilt disease. This disease has been prevalent in some countries in Asia since the 1970s. An amplified fragment length polymorphism survey was used to compare the genetic variation of native and invasive nematode populations in China and to examine the changes in genetic diversity during the invasion process. The genetic diversity of Chinese populations was slightly higher than that of American populations. Analysis of groups sampled from different invasive stages in China, showed that no obvious change in genetic diversity. Hence, genetic drift and founder effects are not obvious in the invasion process. Phylogenetic analysis showed that Chinese pinewood nematode populations were closer to Japanese populations than to American populations. On the basis of the genetic relationships among samples, two major invasion pathways in China are suggested. One is from Guangdong to Anhui and Zhejiang, and the other is from Guangdong to Jiangsu and then from Jiangsu to Hubei, Guizhong and Congqing. The results imply that it is important to reinforce both domestic and international quarantine to control the spread of pinewood nematode.

The Effects of Founding Events and Agricultural Practices on the Genetic Structure of Three Metapopulations of Globodera pallida

To assess the genetic constitution of the Globodera pallida populations in the Netherlands and the effects of agricultural practices, three geographically separated metapopulations, in total consisting of 226 local populations, were analyzed by two-dimensional gel electrophoresis (2-DGE) of total proteins. This technique allows the accurate assessment of allele frequencies in homogenates of mixtures of individuals. Based on the estimated average heterozygosity, the average proportion of polymorphic loci and the average number of alleles per locus, the genetic diversity among 226 local G. pallida populations was small. The small genetic basis of G. pallida in the Netherlands will facilitate the identification of Solanum genotypes with a broad and durable resistance to G. pallida. Instead of clusters of local populations with unique alleles, a continuous range of allele frequencies was observed. Analysis of the three metapopulations by the Shannon-Weaver index and Nei's G(ST) revealed that the metapopulation from a region with sandy-loam soils was clearly distinguishable from the remaining two; the local populations within this metapopulation were more similar and the genetic diversity within the individual local populations was significantly higher than the local populations from the two remaining regions. These regions are characterized by wider crop rotation schemes and a very limited use of nematicides. The less intensive cultivation of potatoes in these regions with sandy-clay soils resulted in relatively little variation within and more variation between local nematode populations. To our knowledge, the effects of agricultural practices on the genetic constitution of potato cyst nematode populations have not been pinpointed before.

The pinewood nematode: regulation and mitigation

In North America, the native pinewood nematode (PWN), Bursaphelenchus xylophilus, kills exotic pines. When inadvertently introduced to Japan and other Asian countries, PWN became a destructive pest of pines. The PWN has been intercepted in pine shipments from North America to Europe, where there is concern that it may also kill pines and other conifers. To protect their forests from the PWN and other pests, the European Union and other countries now regulate the import of all coniferous chips, sawn wood, and logs. Several species of Bursaphelenchus have a phoretic relationship with Monochamus spp., which carry them to recently felled logs and dead or dying conifers, particularly pines. As a result, species of Monochamus, Bursaphelenchus, or both may be found in chips, unseasoned lumber, and logs. During the past decade, procedures to disinfest transported unprocessed wood have been investigated. These mitigation measures include prevention, host selection, and treatment by fumigation, irradiation, chemical dips, and elevated temperatures.

DNA profiling of Bursaphelenchus species

A 1190-bp DNA fragment, designated X14, was isolated from a Bursaphelenchus xylophilus (isolate J10) genomic library. Used as a probe for DNA profiling, this fragment identifies the pinewood nematode (Bursaphelenchus spp.) at both the species and isolate level. The DNA profiles of a number of different species and isolates hybridised with the X14 probe, are presented. The nucleotide sequence of the 1190-bp probe was determined. Secondary structure analysis identified a large imperfect inverted repeat (IR) element within the probe which could form a large stem-loop structure in the RNA.

Cloning and characterization of a highly conserved satellite DNA sequence specific for the phytoparasitic nematode Bursaphelenchus xylophilus

The phytoparasitic nematode, Bursaphelenchus xylophilus, contains an unusually abundant satellite DNA which constitutes up to 30% of its genome. It is represented as a tandemly repeated MspI-site-containing sequence with a monomeric unit of 160 bp. Thirteen monomers were cloned and sequenced. The consensus sequence is 62% A+T-rich, with the presence of direct and inverted repeat clusters. Monomers of the sequence are very similar, showing on average 3.9% divergence from the calculated consensus. The results suggest that some homogenizing mechanism is acting to maintain the homogeneity of this satellite DNA despite its abundance and that it is not transcribed.