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In order to clarify the role of Pl PMI3 resistance gene in sunflower differential lines D4 for differentiation the pathogenicity in Plasmopara halstedii (sunflower downy mildew), analyses were carried out in two groups including four pathotypes which overcome and do not overcome Pl PMI3 (Pl gene has still not been mapped) resistance gene. Based on the reaction for the P. halstedii isolates to sunflower hybrids varying only in Pl resistance genes, there were no virulence differences for the two groups. Index of aggressiveness was calculated for pathogen isolates and revealed the presence of significant differences between isolates of races 304 and 314; however, there were no aggressiveness differences for 7xx races. Regarding the life-history trait and the genetic architecture of the pathogen: there were morphological and genetic variations for the four P. halstedii isolates without a correlation with pathogenic diversity. The importance of the Pl PMI3 resistance gene to differentiate the pathogenicity in sunflower downy mildew was discussed.

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Phenotypic groups including pathogenic, morphological and genetic characteristics for 50 Plasmopara halstedii (downy mildew) isolates belonging to seven races based on interactions with sunflower plants were revealed. Pathogenicity for pathogen isolates were analysed in sunflower plants showing different levels of resistance. Based on the reaction for the P. halstedii isolates to sunflower hybrids varying only in Pl resistance genes, there were three identified groups based on virulence reaction. Index of aggressiveness was calculated for pathogen isolates and revealed the presence of significant differences between isolates of 100 and 3xx races (more aggressive) and isolates of 710 and 7xx races (less aggressive). Morphological analyses were carried out on zoosporangia and sporangiophores for P. halstedii isolates produced on the surface of cotyledons in sunflower plants infected thought roots. There were no groups based on the morphology of zoosporangia and sporangiophores for pathogen isolates. Genetic relationships were detected between pathogen isolates using 12 EST-derived markers. There was no intra-race genetic variation, but five genetically-identified groups were detected among pathogen isolates of all races. Combining data of pathogen’s variation with variability in sunflower to arrive at durable resistance against P. halstedii was discussed.

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European Journal of Microbiology and Immunology
Authors:
Manja Boehm
,
Ingrid Haenel
,
Benjamin Hoy
,
Lone Brøndsted
,
Todd G. Smith
,
Timothy Hoover
,
Silja Wessler
, and
Nicole Tegtmeyer

Miller 1999 A new pathway for the secretion of virulence factors by bacteria: The flagellar export apparatus functions as a protein-secretion system Proc Natl Acad Sci U S A

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Pathogenicity including virulence and aggressiveness characteristics was studied on three Plasmopara halstedii (the causal agent of downy mildew) isolates of races 710, 714 and 704 using five single zoosporangium isolates per pathogen isolate. Based on the reaction for the P. halstedii isolates to four sunflower hybrids H1 to H4 varying only in their downy mildew resistance genes, there were differences in virulence spectrum in pathogen isolates. Analysis of five single zoosporangium isolates for P. halstedii isolates showed significant variability within pathogen isolate for all aggressiveness criteria. There were no significant differences among pathogen isolates for all aggressiveness criteria. There were significant differences in the morphology of zoosporangia and sporangiophores for pathogen isolates. Genetic relationships were detected between pathogen isolates using 12 EST-derived markers. There was no intra-race genetic variation, but three genetically-identified groups were detected among pathogen isolates.

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The fast evolution of Plasmopara halstedii (downy mildew) remains a major risk for sunflower crop, as new races of the pathogen are bypassing the resistance of sunflower hybrids. In order to understand the processes which led a new virulence to appear in a local P. halstedii population, the genetic relationships were studied using 12 EST (Expressed Sequence Tag)-derived markers between five progeny isolates of races 300, 304, 314, 704 and 714 and two parental ones of races 100 and 710. All genetic analyses were carried out using five single zoosporangium isolates per P. halstedii isolate. There was no intra-isolate genetic variation among the seven pathogen isolates and five multilocus genotypes (MLG) were identified among the 35 P. halstedii single zoosporangium isolates. The single zoosporangium isolates of races 314, 704 and 714 had an intermediary genetic position between the single zoosporangium isolates of two parental isolates. The single zoosporangium isolates of three isolates of races 100, 300 and 304 were localized in the same genetic clade. Two genetic mechanisms could explain the emergence of new virulence in P. halstedii as a recombination between races and mutations in a clonal lineage.

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European Journal of Microbiology and Immunology
Authors:
Hagen Frickmann
,
Andreas Hahn
,
Stefan Berlec
,
Johannes Ulrich
,
Moritz Jansson
,
Norbert Georg Schwarz
,
Philipp Warnke
, and
Andreas Podbielski

–Valentine leukocidin, and bi-component pore-forming toxins are prominent virulence factors that have been associated with skin and soft tissue infections due to S. aureus [ 51 – 54 ]. Admittedly, molecular screening for virulence factors was beyond the scope of this

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Acta Alimentaria
Authors:
A. Castro
,
C. Palhau
,
S. Cunha
,
S. Camarinha
,
J. Silva
, and
P. Teixeira

Staphylococcus aureus is considered a global community and health care pathogen responsible for staphylococcal food poisoning. The aim of this study was to characterize several isolates of S. aureus recovered from different food products concerning enterotoxin genes and other virulence factors including antimicrobial resistance. In 2009, a total of 78 coagulase-positive staphylococci from 1454 food samples were identified to species level; 73 were confirmed as S. aureus. Of the S. aureus isolates 5.5% were resistant to oxacillin, 52.0% showed resistance to erythromycin, and 45.2% to tetracycline. Multidrug resistance was observed in 33.3% of the isolates (resistance to three or more antibiotics of different classes). SCCmec types IV and V were detected among methicillin-resistant S. aureus (MRSA). One MRSA isolate was pvl positive. The 52.0% of food isolates were shown to be enterotoxigenic; egc (63.0%), secbov (44.7%) were the main detected SEs. tst gene was also detected in food isolates. The present work demonstrates the presence of virulent S. aureus collected in 2009 in foods.

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European Journal of Microbiology and Immunology
Authors:
Manja Boehm
,
Daniel Simson
,
Ulrike Escher
,
Anna-Maria Schmidt
,
Stefan Bereswill
,
Nicole Tegtmeyer
,
Steffen Backert
, and
Markus M. Heimesaat

–Barré syndromes [ 10 , 18 , 19 ]. Multiple efforts to unravel the molecular mechanisms of C. jejuni virulence have identified a number of bacterial factors that have a role in the pathogenesis of this organism, but their exact activities and interplay

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Casulli, F., Pasquini, M. 1993. Virulenza delle popolazioni di Puccinia recondita f.sp. tritici e P. graminis f.sp. tritici in Italia (Virulence of Puccinia recondita f.sp. tritici and P. graminis f

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, Schmiel DH, Miller VL: A new pathway for the secretion of virulence factors by bacteria: the flagellar export apparatus functions as a protein-secretion system. Proc Natl Acad Sci USA 96, 6456–6461 (1999) Miller VL

Open access