A multiplex quantitative real time PCR to detect Xanthomonas axonopodis pv.allii from onion seeds : [P2-26]

Bacterial blight of onion is a seed-borne emerging disease threatening world onion production, and causing damage to other Allium crops. Its causal agent, #Xanthomonas axonopodis pv. Allii# (Xaa) is listed in quarantine European and Mediterranean Protection Plant Organization (EPPO) A1 list since 2009. The development of a reliable tool is necessary to manage Xaa spreading via international seed trade. We developed a triplex quantitative real-time PCR capable of detecting Xaa using the Taqman® technology. This quantitative PCR targets two markers specific from Xaa (1) and an internal control chosen in NADH dehydrogenase from Alliaceae. The multiplex real-time PCR was assayed on a large collection of Xaa strains isolated worldwide and pathogenic to onion or to other Allium species. Xaa strains were detected by the amplification of one or both of the two specific markers. In case of poor or no amplification of these Xaa markers, the internal control signal validates both the extraction process and the reaction itself. Specificity was assayed on 80 Xaa strains, and 120 non target strains belonging to other #X. axonopodis# pathovars including strains from the same #X. axonopodis# subgroup 9.2 sensu Rademaker, other species, other genera, and saprophytic strains isolated from onion seed and plants. We obtained standard curves with high correlation coefficients (r2> 0,99) and amplification efficiencies of more than 90% on bacterial suspension (107 to 103 CFU/ml), and efficiencies of more than 80% from seed macerate, allowing the detection of 5.103 to 5.107 CFU/g for seed artificially inoculated with Xaa strains. We successfully detected both bacterial DNA and internal control DNA from plant by performing two successive steps: homogenization of a seed macerate with a stomacher®, followed by DNA extraction using DNeasy Plant minikit (Qiagen). We are currently validating our assay on naturally contaminated seed lots. This tool would be useful for the international sanitary surveillance of seed exchanges. (Résumé d'auteur

Visacane, an innovative quarantine tool for the exchange of pest and disease-free sugarcane germplasm

Sugarcane varietal improvement can not exclusively rely upon exchange and introduction of genetic resources via true seeds (fuzz). It also requires the introduction of vegetative propagation material (cuttings, tissue-cultured plantlets). The continued increase in international and intercontinental trade in plants has led to the enforcement of quarantine measures before introduction into a country because many plant pathogens can be carried and transmitted by vegetatively propagated material. Visacane is the new name of Cirad's sugarcane quarantine (http://visacane.cirad.fr/en/). It covers three main quarantine procedures: detection of pests and pathogens, elimination of pests and pathogens, and transfer of plant material free of pests and pathogens. It has been devoted to sugarcane quarantining for several decades. Besides phytosanitary constraints, Visacane takes also into account legal constraints and ensures, through appropriate contracts, that plant breeders' intellectual property rights over the transferred material are respected. Unlike most sugarcane quarantines that are essentially used to import sugarcane germplasm into a country, Visacane can import and export varieties from and to most sugarcane growing countries in the world, ensuring that the material is free from any important pest and disease causing pathogen. Until recently, the sugarcane quarantine process was aimed at detecting known pathogens harbored by the plant material and eliminating these pathogens whenever possible. It is an a priori process, because it only takes into account the pathogens that have been previously described and for which efficient detection tools exist. During the last three decades, several new viruses infecting sugarcane have been discovered, including Sugarcane bacilliform virus, Sugarcane yellow leaf virus, Sugarcane streak mosaic virus and the virus associated with Ramu stunt. In addition, the etiology of chlorotic streak, a disease known since 1929, has not been elucidated so far, although there is evidence for its infectious nature. Therefore, it can be assumed that unknown pathogens are still to be discovered in sugarcane, especially if these pathogens do not cause symptoms that can be easily observed. For these reasons, the research team associated with Visacane is setting up a new strategy of diagnostics, the so-called sequence-independent approach which aims at deciphering the virome (= the genomes of all the viruses that inhabit a particular organism). We believe that our forthcoming combined process, that will include our traditional approaches in addition to the metagenomics approach, will drastically improve our routine quarantine diagnostics. (Texte intégral

Multi-scale engineering for neuronal cell growth and differentiation

In this paper we investigate the role of micropatterning and molecular coating for cell culture and differentiation of neuronal cells (Neuro2a cell line) on a polydimethylsiloxane substrate. We investigate arrays of micrometric grooves (line and space) capable to guide neurite along their axis. We demonstrate that pattern dimensions play a major role due to the deformation of the cell occasioned by grooves narrower than typical cell dimension. A technological compromise for optimizing cell density, differentiation rate and neurite alignment has been obtained for 20 lm wide grooves which is a dimension comparable with the average cell dimension. This topographical engineered pattern combined with double-wall carbon nanotubes coating enabled us to obtain adherent cell densities in the order of 104 cells/cm2 and a differentiation rate close to 100%

Visacane, the Cirad quarantine tool for the exchange of pest and disease-free sugarcane germplasm

Sugarcane varietal improvement requires the introduction of vegetative propagation material. The continued increase of international and intercontinental trade of plants has led to the enforcement of quarantine measures in many countries before the introduction of vegetatively propagated material because many plant pathogens can be carried and transmitted by them. Visacane is the CIRAD's sugarcane quarantine (http://visacane.cirad.fr/en/). Visacane has been devoted to sugarcane quarantining for several decades. It covers detection of pests and pathogens, elimination of pests and pathogens, and transfer of plant material free of pests and pathogens. Besides phytosanitary constraints, this quarantine structure also takes into account legal constraints and ensures that plant breeders' intellectual property rights over the transferred material are respected. Visacane can import and export varieties from and to most sugarcane growing countries in the world, ensuring that the material is free from any well-known important pest and disease causing agent. Because it is integrated into a pathology research unit studying various aspects of plant-pathogen interactions, and thanks to its collaborations within a network of sugarcane technologists, Visacane can regularly update its expertise and propose plant material exhibiting the best possible phytosanitary quality. (Résumé d'auteur

PCR-based assays for detecting Xanthomonas axonopodis pv. allii in onion seed

Bacterial blight of onion is an emerging disease threatening world onion production, and causing damage to other Allium crops. The causal agent, Xanthomonas axonopodis pv. allii (Xaa) has been listed on the EPPO A1 list of pests recommended for regulation as quarantine pests, since 2009. A duplex nested-PCR assay, targeting two markers specific to Xaa has been recently developed (Robène-Soustrade et al., 2010). A triplex quantitative real-time PCR assay (Taqman® technology) was developed targeting the same Xaa-specific markers and an internal control chosen in 5.8S rRNA gene from Alliaceae. Xaa strains were detected by the amplification of one or both of the two specific markers. The internal control signal validates both the extraction process and the reaction itself. Several successive steps have to be performed before detection from seed: seed maceration for 48h at 4°C, followed by homogenization of the seed macerate with a stomacher® and DNA extraction using DNeasy® Plant mini kit (Qiagen). This assay is currently being validated following the European standard EN ISO 16140: 2003 and the EPPO standard PM7/98 (1). The performance of Nested-PCR and real-time PCR assays are discussed. These PCR-based tools could be useful for the international sanitary surveillance of seed exchanges. (Résumé d'auteur

Statactivism: forms of action between disclosure and affirmation

This article introduces the special issue on statactivism, a particular form of action within the repertoire used by contemporary social movements: the mobilization of statistics. Traditionally, statistics has been used by the worker movement within the class conflicts. But in the current configuration of state restructuring, new accumulation regimes, and changes in work organization in capitalists societies, the activist use of statistics is moving. This first article seeks to show the use of statistics and quantification in contentious performances connected with state restructuring, main transformations of the varieties of capitalisms, and changes in work organization regimes. The double role of statistics in representing as well as criticizing reality is considered. After showing how important statistical tools are in producing a shared reading of reality, we will discuss the two main dimensions of statactivism – disclosure and affirmation. In other words, we will see the role of stat-activists in denouncing a certain state of reality, and then the efforts to use statistics in creating equivalency among disparate conditions and in cementing emerging social categories. Finally, we present the main contributions of the various research papers in this special issue regarding the use of statistics as a form of action within a larger repertoire of contentious action. Six empirical papers focus on statactivism against the penal machinery in the early 1970s (Grégory Salle), on the mobilisation on the price index in Guadalupe in 2009 (Boris Samuel), and in Argentina in 2007 (Celia Lury and Ana Gross), on the mobilisations of experts to consolidate a link between working conditions and health issues (Marion Gilles), on the production of activity data for disability policy in France (Pierre-Yves Baudot), and on the use of statistics in social mobilizations for gender equality (Eugenia De Rosa). Alain Desrosières wrote the last paper, coping with mobilizations proposing innovations in the way of measuring inflation, unemployment, poverty, GDP, and climate change. This special issue is dedicated to him, in order to honor his everlasting intellectual legac