1,721,167 research outputs found
Evolution of populations of cucurbit-infecting potyviruses in France: insights into the mechanisms of plant virus emergence
No full textWatermelon mosaic virus (WMV) and Zucchini yellow mosaic virus (ZYMV) are among the major cucurbit-infecting viruses worldwide. In France, WMV has a high prevalence every year throughout the growing season; ZYMV, although it can present locally a very high agronomic impact, induces epidemics that are very irregular both in spatial distribution and timing of infection. Large-scale epidemiological surveys followed by molecular analysis of all collected samples were performed during 5 years in France, and revealed the recent appearance of new, “emerging” (EM) isolates of both viruses in south-eastern France. In the case of WMV, four subgroups of EM isolates were defined, probably resulting from several recent introductions. They presented a strong geographic structure that remained stable over 5 years, and tended to replace rapidly the original “classic” isolates in areas where both types of strains were present. For ZYMV, at least two subgroups of new isolates were also detected in the last years, although the geographic structure of infections and evolution of populations was less obvious than for WMV. In order to characterize the evolution of viral populations and study the mechanisms favouring or limiting viral emergence and spread, several complementary approaches were developed: multilocal and multiscale epidemiological studies, molecular analyses and population genetics, as well as estimation of viral fitness in experimental condition and modeling. The risks of emergence of recombinants between “classic” and EM populations in the few years following their contact were also assessed
A simple, rapid and efficient way to obtain infectious clones of potyviruses
No full textThe availability of an infectious cDNA clone is a prerequisite for genetic studies on RNA viruses. However, despite important improvement in molecular biology techniques during the last decades, obtaining such clones often remains tedious, time-consuming and rather unpredictable. In the case of potyviruses, cDNA clones are frequently unstable due to the toxicity of some viral proteins for bacteria. The problem can be overcome by inserting introns into the viral sequence but this requires additional steps in the cloning process and depends on the availability of suitable restriction sites in the viral sequence or adjunction of such sites by mutagenesis. Homologous recombination in yeast rather than in vitro restriction and ligation can be used to build infectious clones or other viral constructs. This paper describes how, by using recombination in yeast and fusion PCR, infectious intron-containing clones were obtained within a few weeks for two strains of watermelon mosaic virus (WMV, Potyvirus), whereas previous attempts using “classical” cloning techniques had failed repeatedly. Using the same approach, intronless infectious clones of two other potyviruses, zucchini yellow mosaic virus (ZYMV) and papaya ringspot virus (PRSV), were obtained in less than two week
Do recombinants appearing in natural populations of watermelon mosaic virus represent new agronomic threats?
No full textWatermelon mosaic virus (WMV, Potyvirus) is very common in France where it has been present for at least 40 years. Since the early 2000s, new “emerging” (EM) strains of WMV, highly divergent molecularly from the “classic” (CL) strains present before and probably originating from recent introductions, were detected in southeastern France. Since both types of strains did not appear to be present in the same geographic locations before, this situation constituted a unique opportunity to study the frequency of appearance and the potential spread of recombinants in the few years following the introduction of the new strains. Analyzing isolates from experimental plots in Montfavet (Southeastern France) as well as from epidemiological surveys performed from 2004 to 2008 all around France (about 2000 WMV isolates) revealed at least 7 independent recombination events, either between CL and EM strains or between different EM subgroups. Most recombinants were found in a few plants from the same field, but, with one notable exception, did not seem to spread or be maintained locally for several years. Mixed infections of CL and EM isolates were also performed in experimental conditions in order to compare the frequency and nature of recombination events to those of natural situation. The fitness of natural recombinants relative to potential “parental” strains was also tested in controlled conditions. The epidemiological and evolutionary consequences of recombination in WMV populations will be discussed. This work represents one of the first estimation for the frequency of appearance of recombinants in natural populations of a plant RNA virus
The "PRSV cluster" of cucurbit-infecting potyviruses: how many species, and what is their evolutionary and biological meaning?
No full textCharacterization of an atypical tenui-like virus infecting dicotyledonous plants in France
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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
Viruses of cucurbit crops: a rapidly changing situation related to multiple factors, particularly to frequent virus introductions
No full textInternational audienc
Molecular characterization of cucurbit aphid-borne yellows virus affecting cucurbits in Turkey
No full textCucurbits are economically important vegetable in Turkey. Cucurbit crops are seriously affected by many viruses including Cucurbit aphid-borne yellows virus (CABYV). CABYV, a widespread polerovirus causing yellowing symptoms on older leaves that were previously associated to nutritional or physiological disorders. CABYV was first identified in 1988 in France, now, CABYV is widely spread in the whole Mediterranean region (Lecoq and Desbiez 2012). In Turkey, CABY reported firstly by Yardımcı and Özgönen (2007) as serologicaly. The purpose of this study was to characterize the molecular variability of CABYV in Turkey, through determining partial coat protein (CP) nucleotide sequences of (CABYV) isolates of Turkey
Mémoire pour obtenir l'habilitation à diriger des recherches
No full text1 annexe (57 p., 7 publications) Diplôme : HD
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