1,720,956 research outputs found
Grapevine collections free from pathogens: tools and their application
No full textThe grapevine collections are very important tools to maintain grapevine biodiversity and historical germoplasm as well however in several cases especially grapevine from poor cultivated or non commercial varieties could be infected by several graft transmissible pathogens such as viruses, phytoplasmas and other systemic bacteria. In the majority of the cases these pathogens are not inducing evident symptomatology in short time after grafting therefore the possibly infected material of collection could represent a dangerous pathogen reservoir.
In order to control pathogen presence in already made collections and to prevent the spreading of the above pathogens together with the grapevine germplasm to other collections. Then, it is mandatory to exclude presence of quarantine pathogens such as “flavescece dorée” (FD) phytoplasmas and advisable to exclude relevant pathogens for quality such as viruses and phytoplasmas agent of “bois noir”, by using the most sensitive detection techniques available. It is advisable however to acquire any possible information concerning the phytosanitary status of the circulating grapevine material in order to prevent possible unforeseen outbreak of disease such as those occurred for FD disease when a grapevine insect such as Scaphoideus titanus (previously named Scaphoideus littoralis) was introduced in Europe. It is known in fact that a high number of different phytoplasmas are able to infect grapevine worldwide in the presence of appropriate insect vector or by grafting or micropropagation techniques application and crown gall is an old severely remerging disease at least in the major viticultural areas of EU and US.
First step before transferring germplasm among collection must be the verification of their sanitary status taking into account that tests to verify virus and bacteria presence should be carried out preferably during winter/spring time while those to detect phytoplasmas are more sensitive in Summer and Fall periods and the most sensitive techniques such as ELISA and PCR must be employed.
In the case of germplasm having no clean plants available after the survey it is necessary to clean the material using thermotherapy and or shoot tip culture in order to eliminate the pathogens. These techniques are not eliminating the pathogens from all the produced material therefore molecular tests are again necessary to assess the grapevine health status before the material can be employed for collection and/or field dissemination. In case of virus or phytoplasma infected grapevine germplasm of unique genetic value it must be maintained under insect proof condition while it is infected in order to avoid contamination of other germplasm in the same collection. In the same way the clean germplams should also be protected in insect proof environment in order to avoid its recontamination. It is also very important to keep the collection clean from insect that are virus (mealy bugs and scale insects) or phytoplasma vectors (leafhopper and cixiids) and also the soil must be clean from Agrobacterium tumefaciens and collection should be protected from frost or mechanical damages increasing crown gall dissemination
Phytoplasmas associated with grapevine yellows diseases: an overview
No full textPhytoplasmas are obligate intracellular bacterial parasites restricted to the phloem sieve elements of the infected plants and are transmitted by phloem-sucking insects belonging to the families Cicadellidae, Cixidae, Psyllidae, Delphacidae and Derbidae. They are associated with diseases of several hundred plant species, including some economically important crops. Grapevine yellows (GY) is a worldwide disease complex associated with genetically different phytoplasmas. GY-affected Vitis vinifera shows leaf enrollment accompanied by yellowing or reddening, rubbering of the canes and desiccated clusters. Epidemiology of the different GY diseases, undistinguishable based on symptoms observation, strictly depends on the involved phytoplasma because of the insect-vector specificity and their behavior. GY diseases are attributed to infections by at least nine distinct phytoplasmas. In Europe, “flavescence dorée” (FD) and Palatinate grapevine yellows (PGY, present only in Germany), are associated with phytoplasmas classified in the ribosomal group 16SrV, while “bois noir” (BN) is attributed to phytoplasmas classified in stolbur group (ribosomal subgroup 16SrXII-A). In Australia, Australian grapevine yellows is associated to ‘Candidatus Phytoplasma australiense’ (ribosomal subgroup 16SrXII-B), and to ‘Ca. P. aurantifolia’ (ribosomal group 16SrII). Grapevine yellows in Virginia is associated with a ‘Ca. P. asteris’-related strain (ribosomal group 16SrI-A) and X-disease group (ribosomal group 16SrIII) phytoplasmas. In Chile ‘Ca. P. fraxini’ was also associated with GY together with stolbur and 16SrI-B and 16SrI-C phytoplasmas. In Italy and in South Africa ‘Ca. P. asteris’ (16SrI-B) was associated with severe GY epidemics as well. In order to distinguish each GY from the others, an important research topic focuses on developing molecular tools for specific phytoplasmas identification. In Europe, the employment of such methods for the certain exclusion of FD and BN phytoplasmas from grapevine certified propagating material is becoming urgent. PCR-based techniques allowed development of useful tools for the identification of phytoplasmas; standard protocols include nested PCR amplification of phytoplasma 16S rDNA using universal or group specific primers and RFLP analyses in order to determine the taxonomic (ribosomal group/subgroup) affiliation. Further molecular characterization, performed by sequence analyses on genes less conserved than 16S rDNA, found additional markers useful for developing suitable analytical tests for faster and specific detection of FD and BN phytoplasmas. Up to now, innovative molecular approaches developed to this aim are: (i) Real Time PCR and reverse transcription – Real Time PCR for the detection of phytoplasmas associated with FD and BN; (ii) nanobiotransducer for detecting FD phytoplasmas; (iii) multiplex nested PCR for simultaneous identification of FD and BN phytoplasmas; (iv) Ligase Detection Reaction (LDR) DNA microarray to detect and distinguish FD and BN phytoplasmas.
Furthermore, multiple gene sequence analyses (Multi Locus Sequence Typing, MLST) on ribosomal (rplV-rpsC) and non ribosomal (secY, map, uvrB, degV, hlyC, vmp, and tuf) genes highlighted an unexpected genetic heterogeneity among both FD and BN phytoplasma populations, identifying different FD and BN phytoplasma strains that can be associated with specific ecological niches (plant hosts, insect vectors, geographic origin). MLST analyses improved the chance to associate phytoplasma-specific molecular markers with biological features, opening new perspectives for the studies of FD and BN epidemiology
Grapevine crown gall: an old, emerging disease.
No full textCrown gall is considered one of the most important and widespread bacterial diseases of grapevine (Vitis vinifera L.) throughout the world. It is known in Europe for more than 150 years and can be still of great phytopathologic significance in the vineyards and nurseries, especially in cold-climate regions. The disease is predominantly caused by tumorigenic strains of Agrobacterium vitis, more rarely by tumorigenic A. tumefaciens and A. rhizogenes. Unlike A. tumefaciens and A. rhizogenes, that are broad-host-range pathogens, A. vitis is specific to grapevine. Crown gall reduces vigor and yield of grapevines and severe disease may cause partial or complete death of infected plants. High losses occur in nurseries where different graft combinations with visible symptoms are unmarketable and must be discarded. Typical symptoms of crown gall are tissue proliferation (tumors) formed mostly on the lower areas of the trunk and on aerial canes. Tumorigenic and nontumorigenic strains of A. vitis are also able to cause specific root decay and it has been hypothesized that both types may be factors involved in the “replant disease” syndrome. Wounds mainly caused by freezing temperatures or grafting serve as a crucial entry points for the pathogen and its complex infection process. During the infection process DNA fragment from the bacterial tumor inducing (Ti) plasmid is transferred and integrated into the plant genome (interkingdom gene transfer). This leads to the overproduction of the phytohormones auxin and cytokinin, resulting in an uncontrolled proliferation of plant cells and tumor formation. A. vitis is unevenly distributed within systemically infected grapevines and able to survive in vineyard soil, particularly in the vicinity of infected plants and in their debris. Another important aspect is the ability of the pathogen to be latently present within the grapevine, providing an important means of spread over short and long distances by asymptomatic propagation material. Management of grapevine crown gall is not easy considering that no effective chemical control measures are available. However, production of A. vitis-free grapevines is an essential prerequisite for an effective prevention of the disease, and great efforts should be done in this direction. For this reason, shoot tip propagation of grapevine and thermotherapy are available as control measures. Planting of crown gall and cold-resistant cultivars and rootstocks would be a good practice when establishing new vineyards. Biological control of crown gall is another promising approach in the control of the disease and several antagonistic bacterial strains have shown a certain level of efficiency in preventing tumor formation. Indexing of grapevines for the endophytic presence of A. vitis is a very important preventive measure.
Differentiation and identification of tumorigenic strains can be rapidly assessed by PCR using primer combinations specific for bacterial Ti plasmid and chromosomal genes. However, a high level of genetic diversity among Agrobacterium strains may limit the efficiency of PCR. In our studies virC, virD, virF, pehA and 23S rRNA gene-specific primers (Bini et al., Vitis 47:181, 2008; Pulawska et al., Syst. Appl. Microbiol. 29:470, 2006; Suzaki et al., J. Gen. Plant Pathol. 70:342, 2004; Szegedi and Bottka, Vitis 41:37, 2002) were reliable in routine detection and identification of a broad range of Agrobacterium strains occurring in grapevine. However, there is necessity for development and standardization of indexing procedures including protocols of analysis and sampling methods. In the EU and many other European countries, A. vitis is not listed as a quarantine pathogen and is considered as a “quality organism” which significantly reduces the value of propagation material. Therefore, the importance of proper phytosanitary measures in grapevine nurseries and on commercial lots should be emphasized
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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