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A new bacterial disease of Persian (English) walnut ( Juglans regia) has been observed in France. This disease, called vertical oozing canker (VOC), is characterized by vertical cankers on trunks and branches of affected walnut trees with oozing exudates. To determine the aetiology of the disease, a study was carried out in 79 walnut orchards and nurseries located in southeastern and southwestern France. Bacterial analysis from diseased samples yielded 36 strains identified as Xanthomonas arboricola and 32 strains identified as Brenneria nigrifluens on the basis of biochemical tests. The causal agent of VOC was identified as X. arboricola by pathogenicity tests on walnut. Fluorescent amplified fragment length polymorphism (F-AFLP) was carried out on 36 strains of X. arboricola collected in this study, 24 strains of X. arboricola pv. juglandis isolated from walnut blight symptoms and one strain of X. arboricola pv. corylina included as an outgroup. Based on cluster analysis of F-AFLP data, most X. arboricola strains responsible for main VOC outbreaks showed a high degree of similarity, forming a cluster clearly separate from strains of X. arboricola pv. juglandis isolated from walnut blight symptoms. It is suggested that VOC is caused by a distinct genetic lineage within the pathovar juglandis of X. arboricola that is also able to cause classical bacterial blight symptoms on walnut leaves and fruits. [ABSTRACT FROM AUTHOR]

Xylophilus ampelinusis listed as a quarantine pest in Annex II/A2 of EU Directive 2000/29. Grapevine cuttings used either as rooting or grafting material represent a primary source of inoculum because of the systemic nature of bacterial colonization. We describe a PCR-based method for the specific detection ofX. ampelinusfrom various plant materials (trunks, woody branches, growing shoots, leaves and bleeding sap), making the detection ofX. ampelinusreliable throughout the year. Bacterial cells were extracted by crushing the plant tissues and soaking them in sterile distilled water for 30–120 min at 4 °C. Bacterial cells were harvested by centrifugation at 13 000gfor 10 min through sterile paper discs, and lysed in SDS buffer. DNA was extracted by a silica-based procedure. Specific DNA amplifications were performed with a pair of primers, of which one was labelled with biotin. A digoxygenin-labelled oligonucleotide with a sequence specific for the amplicon was used as the probe. Finally, amplicons were immobilized in microplate wells coated with streptavidine, and hybridization of the digoxygenin-labelled probe was detected with alkaline phosphatase-conjugated antibiodies in a colorimetric assay. This method was sensitive, specific and allowed experiments with high throughput. [ABSTRACT FROM AUTHOR]

Friction experiments between two austenitic stainless steel (AISI 304L) surfaces in sliding contact were carried out under very low loads in two liquid environments, namely demineralized water and methanol, in order to study the correlation between surface damage (wear and surface topography) and structural modifications (phase formation and microstructure). The particularity of our approach was to perform the tests under Hertzian pressures, which were several orders of magnitude lower than the elastic limit of stainless steel. The structural modifications produced during friction were analysed by X-ray diffraction and transmission electron microscopy and the surface topography was studied by scanning electron microscopy and three-dimensional (3D) profiling. Whatever the experimental conditions investigated, the morphology of the damage observed on both surfaces consisted of very fine, smooth and parallel grooves typical of an abrasive wear process of a ductile material caused by the ploughing action of hard particles. From the beginning of the tests, the transformation of austenite into martensite was observed in the superficial layers and the dominant presence of martensite was identified in the wear debris. These results suggest that, under our experimental conditions, abrasion is the dominant mechanism of material removal. [ABSTRACT FROM AUTHOR]

Ball-on-flat friction experiments between two austenitic stainless steel antagonists in sliding contact are carried out under very low loads and in two liquid environments, namely demineralized water and methanol. The wear debris produced during long-duration tests are characterized by different techniques such as X-ray diffraction, transmission electron microscopy and Mössbauer spectroscopy. Martensite is observed as a dominant phase in the wear debris but other phases have been also identified. In the debris produced under demineralized water, there is significant contribution of a second phase, which is poorly crystallized and which was identified as the hydrous iron oxide called ferrihydrite. In the debris produced under methanol, there is a remaining amount of austenite that is not transformed into martensite, and the presence of ferrihydrite has been also detected in very small quantities. The formation of the martensitic debris which occurs from the beginning of the wear tests supports the fact that under our experimental conditions the main damaging mode is abrasive wear by hard particles. [ABSTRACT FROM AUTHOR]