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Nachaat Sakr - One of the best experts on this subject based on the ideXlab platform.
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Interaction between sunflower plants and five isolates of Plasmopara halstedii on the level of pathogenicity
Journal of Plant Interactions, 2015Co-Authors: Nachaat SakrAbstract:The interaction between sunflower plants showing a high level of quantitative resistance and five Plasmopara halstedii (the causal agent of downy mildew) isolates of several races were studied using five single zoosporangium isolates per pathogen isolate. Aggressiveness criteria were analyzed for 25 P. halstedii single zoosporangium isolates. Based on the reaction for the P. halstedii isolates to four sunflower hybrids H1-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 but not for all pathogen isolates. The hypothesis explaining the interaction between P. halstedii and its host plant was discussed on the level of pathogenicity.
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A Method to Measure Aggressiveness of Plasmopara halstedii (Sunflower Downy Mildew)
Journal of Phytopathology, 2015Co-Authors: Nachaat Sakr, Mireille Ducher, Felicity Vear, Jeanne Tourvieille, Pascal Walser, Denis Tourvieille De LabrouheAbstract:For the first time, a method was used to measure aggressiveness of two Plasmopara halstedii races (100 and 710), the parasite causing sunflower downy mildew. Two sunflower lines showing different levels of quantitative resistance were used to measure two aggressiveness criteria: latent period and sporulation density. A strain of race 100 had a shorter latent period and greater sporulation density than a strain of race 710. The sunflower inbred line BT, rather susceptible in the field, presented a greater sporulation density and a shorter latent period than another inbred line FU, which shows greater resistance in the field. These results indicated that race 100 was more aggressive than race 710. The behaviour in the field of the two inbred lines was confirmed in the laboratory observations.
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Variation in form and size of Plasmopara halstedii (sunflower downy mildew) zoosporangia
Mycological Progress, 2015Co-Authors: Nachaat Sakr, Mireille Ducher, Jeanne Tourvieille, Pascal Walser, Denis Tourvieille De LabrouheAbstract:Zoosporangia form and size were studied on a collection of 94 strains of Plasmopara halstedii (sunflower downy mildew). Both oval and round forms were present in all strains analysed. The proportion of two forms varied significantly according to strain and plant age but more especially to host plant genotype. Whatever the strain or host genotype, oval zoosporangia were larger than round ones, but there was no relation between the proportion of the oval form and mean zoosporangia size. There was no relation between zoosporangia form or size and race virulence profiles or aggressiveness criteria, with the possible exception of zoosporangia size and sporulation density. It is concluded that, for this obligate parasite, although form and size of zoosporangia depend on pathogen strain, these characters also vary according to growth conditions of Plasmopara halstedii, in particular to the genotype of the plant host.
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Aggressiveness in Plasmopara halstedii (sunflower downy mildew)
Plant Pathology Journal, 2015Co-Authors: Nachaat SakrAbstract:Aggressiveness was studied in seven Plasmopara halstedii (sunflower downy mildew) pathotypes: 100, 300, 304, 314, 704, 710 and 714. Aggressiveness criteria including percentage infection, latent period, sporulation density and reduction of hypocotyl length (dwarfing) were analysed in one sunflower inbred line showing a high level of quantitative resistance. Genetic relationships were detected between the seven pathotypes using 12 EST-derived markers. Pathotypes 100, 300, 304 and 314 were characterized with shorter latent period and higher sporulation density than pathotypes 710, 704 and 714. All pathotypes showed high percentage infection values and caused a large reduction in seedling size except for pathotype 314 involved in dwarfing. Pathotypes 714, 704 and 314 had an intermediary genetic position between the pathotypes 100 and 710. No correlation was detected between aggressiveness traits and EST genotypes.
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A new method to obtain monozoosporangial isolates of sunflower downy mildew (Plasmopara halstedii)
Cryptogamie Mycologie, 2015Co-Authors: Nachaat Sakr, Mireille Ducher, Jeanne Tourvieille, Pascal Walser, Denis Tourvieille De LabrouheAbstract:A new method to obtain monozoosporangial strains was applied on 9 pathotypes of Plasmopara halstedii (100, 300, 304, 314, 700, 704, 710, 707 and 714), the parasite causing sunflower downy mildew. Single zoosporangia were isolated from the surface of agar medium and placed on leaf disks on solid Knop medium. The best fungal development was obtained with leaf disks taken from the first pair of sunflower leaves when these measured from 5 to 8cm in length. The percentage success rate in obtaining monozoosporangial strains varied from 1.4 to 7.4% according to race. The percentage of disks showing sporulation depends on spore viability, the physiological state of leaves and the receptivity of the sunflower genotype. This method enabled us to confirm the presence of a new downy mildew pathotype in France: race 707.
Denis Tourvieille De Labrouhe - One of the best experts on this subject based on the ideXlab platform.
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An Optimized Duplex Real-Time PCR Tool for Sensitive Detection of the Quarantine Oomycete Plasmopara halstedii in Sunflower Seeds
Phytopathology, 2016Co-Authors: Renaud Ioos, Celine Fourrier, Kathryn Webb, Veronique Wilson, Jean-Luc Schereffer, Denis Tourvieille De LabrouheAbstract:Ioos, R., Fourrier, C., Wilson, V.. Webb, K., Schereffer, J.-L., and Tourvieille de Labrouhe, D. 2012. An optimized duplex real-time PCR tool for sensitive detection of the quarantine oomycete Plasmopara halstedii in sunflower seeds. Phytopathology 102:908-917. Plasmopara halstedii, the causal agent of downy mildew of sunflower, is an oomycete listed as a quarantine pathogen. This obligate parasite resides in a quiescent state in seeds of sunflower and can be spread from seed production areas to areas of crop production by international seed trade. To prevent the spread or the introduction of potentially new genotypes or fungicide-tolerant strains, an efficient method to detect P halstedii in sunflower seed is required. This work reports the optimization of a real-time detection tool that targets the pathogen within sunflower seeds, and provides statistically validated data for that tool. The tool proved to be specific and inclusive, based on computer simulation and in vitro assessments, and could detect as few as 45 copies of target DNA. A fully optimized DNA extraction protocol was also developed starting from a sample of 1,000 sunflower seeds, and enabled the detection of
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A Method to Measure Aggressiveness of Plasmopara halstedii (Sunflower Downy Mildew)
Journal of Phytopathology, 2015Co-Authors: Nachaat Sakr, Mireille Ducher, Felicity Vear, Jeanne Tourvieille, Pascal Walser, Denis Tourvieille De LabrouheAbstract:For the first time, a method was used to measure aggressiveness of two Plasmopara halstedii races (100 and 710), the parasite causing sunflower downy mildew. Two sunflower lines showing different levels of quantitative resistance were used to measure two aggressiveness criteria: latent period and sporulation density. A strain of race 100 had a shorter latent period and greater sporulation density than a strain of race 710. The sunflower inbred line BT, rather susceptible in the field, presented a greater sporulation density and a shorter latent period than another inbred line FU, which shows greater resistance in the field. These results indicated that race 100 was more aggressive than race 710. The behaviour in the field of the two inbred lines was confirmed in the laboratory observations.
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Variation in form and size of Plasmopara halstedii (sunflower downy mildew) zoosporangia
Mycological Progress, 2015Co-Authors: Nachaat Sakr, Mireille Ducher, Jeanne Tourvieille, Pascal Walser, Denis Tourvieille De LabrouheAbstract:Zoosporangia form and size were studied on a collection of 94 strains of Plasmopara halstedii (sunflower downy mildew). Both oval and round forms were present in all strains analysed. The proportion of two forms varied significantly according to strain and plant age but more especially to host plant genotype. Whatever the strain or host genotype, oval zoosporangia were larger than round ones, but there was no relation between the proportion of the oval form and mean zoosporangia size. There was no relation between zoosporangia form or size and race virulence profiles or aggressiveness criteria, with the possible exception of zoosporangia size and sporulation density. It is concluded that, for this obligate parasite, although form and size of zoosporangia depend on pathogen strain, these characters also vary according to growth conditions of Plasmopara halstedii, in particular to the genotype of the plant host.
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Twelve polymorphic expressed sequence tags-derived markers for Plasmopara halstedii, the causal agent of sunflower downy mildew
Molecular Ecology Notes, 2015Co-Authors: Xavier Giresse, Sylvie Richard Cervera, Denis Tourvieille De Labrouhe, François DelmotteAbstract:Twelve expressed sequence tags-derived markers were isolated from Plasmopara halstedii (Oomycetes), the causal agent of sunflower downy mildew. A total of 25 single nucleotide polymorphisms and five indels were detected by single-strand conformation polymorphism analysis and developed for high-throughput genotyping of 32 isolates. There was a high level of genetic diversity (HE = 0.484). Observed heterozygosity ranged from 0 to 0.143 indicating that P. halstedii is probably a selfing species. These markers were also useful in detecting significant genetic variations among French populations (FST = 0.193) and between French and Russian populations (FST = 0.23). Cross-amplification tests on three closely related species indicated that no loci amplified in other Oomycete species.
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A new method to obtain monozoosporangial isolates of sunflower downy mildew (Plasmopara halstedii)
Cryptogamie Mycologie, 2015Co-Authors: Nachaat Sakr, Mireille Ducher, Jeanne Tourvieille, Pascal Walser, Denis Tourvieille De LabrouheAbstract:A new method to obtain monozoosporangial strains was applied on 9 pathotypes of Plasmopara halstedii (100, 300, 304, 314, 700, 704, 710, 707 and 714), the parasite causing sunflower downy mildew. Single zoosporangia were isolated from the surface of agar medium and placed on leaf disks on solid Knop medium. The best fungal development was obtained with leaf disks taken from the first pair of sunflower leaves when these measured from 5 to 8cm in length. The percentage success rate in obtaining monozoosporangial strains varied from 1.4 to 7.4% according to race. The percentage of disks showing sporulation depends on spore viability, the physiological state of leaves and the receptivity of the sunflower genotype. This method enabled us to confirm the presence of a new downy mildew pathotype in France: race 707.
Said Mouzeyar - One of the best experts on this subject based on the ideXlab platform.
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Expressed Sequence Tags from the oomycete Plasmopara halstedii, an obligate parasite of the sunflower
BMC Microbiology, 2015Co-Authors: Mohamed-Fouad Bouzidi, Francis Parlange, Paul Nicolas, Said MouzeyarAbstract:Background: Sunflower downy mildew is a major disease caused by the obligatory biotrophic oomycete Plasmopara halstedii. Little is known about the molecular mechanisms underlying its pathogenicity. In this study we used a genomics approach to gain a first insight into the transcriptome of P. halstedii. Results: To identify genes from the obligatory biotrophic oomycete Plasmopara halstedii that are expressed during infection in sunflower (Helianthus annuus L.) we employed the suppression subtraction hybridization (SSH) method from sunflower seedlings infected by P. halstedii. Using this method and random sequencing of clones, a total of 602 expressed sequence tags (ESTs) corresponding to 230 unique sequence sets were identified. To determine the origin of the unisequences, PCR primers were designed to amplify these gene fragments from genomic DNA isolated either from P. halstedii sporangia or from Helianthus annuus. Only 145 nonredundant ESTs which correspond to a total of 373 ESTs (67.7%) proved to be derived from P. halstedii genes and that are expressed during infection in sunflower. A set of 87 nonredundant sequences were identified as showing matches to sequences deposited in public databases. Nevertheless, about 7% of the ESTs seem to be unique to P. halstedii without any homolog in any public database. Conclusion: A summary of the assignment of nonredundant ESTs to functional categories as well as their relative abundance is listed and discussed. Annotation of the ESTs revealed a number of genes that could function in virulence. We provide a first glimpse into the gene content of P. halstedii. These resources should accelerate research on this important pathogen.
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Expressed Sequence Tags from the oomycete Plasmopara halstedii , an obligate parasite of the sunflower
BMC microbiology, 2007Co-Authors: Mohamed-Fouad Bouzidi, Francis Parlange, P. Nicolas, Said MouzeyarAbstract:Background Sunflower downy mildew is a major disease caused by the obligatory biotrophic oomycete Plasmopara halstedii. Little is known about the molecular mechanisms underlying its pathogenicity. In this study we used a genomics approach to gain a first insight into the transcriptome of P. halstedii.
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Accumulation of Defense Related Transcripts in Sunflower Hypocotyls (Helianthus annuus L.) Infected with Plasmopara halstedii
European Journal of Plant Pathology, 1999Co-Authors: Florence Mazeyrat, Said Mouzeyar, Denis Tourvieille De Labrouhe, Patricia Roeckel-drevet, Isabelle Courbou, Saloua Badaoui, Gérard LedoigtAbstract:A cDNA clone encoding a sunflower chitinase was obtained using degenerated primers in PCR amplifications and RACE procedures. This clone, a phenylalanine ammonia-lyase (PAL) clone and ubiquitin clone were used to analyse the resistance of sunflower (Helianthus annuus) to downy mildew. The differential regulation of amounts of PAL (involved in the general pathway of phenylpropanoid synthesis), chitinase (a pathogenesis-related protein) and ubiquitin (involved in proteolytic pathways) mRNA was studied in hypocotyls during the early stages after an aerial infection of sunflower inbred line RHA274 with zoospores from either race 1 (incompatible, host resistant) or race B (compatible, host susceptible) of Plasmopara halstedii. Northern analyses showed that transcript levels of PAL, chitinase and ubiquitin were rapidly and strongly increased after infection in incompatible interactions but not in the compatible ones, suggesting that regulation of these mRNAs is an important component of the resistance mechanisms in sunflower.
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Colocation of downy mildew (Plasmopara halstedii) resistance genes in sunflower (Helianthus annuus L.)
Euphytica, 1996Co-Authors: Patricia Roeckel-drevet, Said Mouzeyar, P. Nicolas, Denis Tourvieille De Labrouhe, J. Philippon, Geneviève Gagne, Laurent Gentzbittel, Felicity VearAbstract:The Pl6 locus in the inbred sunflower (Helianthus annuus L.) line HA335 giving resistance to French races of downy mildew (Plasmopara halstedii (Farl.) Berl. & de Toni. was localized by molecular techniques. A bulked segregant analysis was made on the F2 progeny from a cross between this line and H52, a downy mildew susceptible line. The resistance gene in HA335 was found to have the same linked RFLP marker loci as those determined for Pl1 (resistance to race 1 in the line RHA266) on linkage group 1 of the consensus RFLP map of the cultivated sunflower. Pl1 and Pl6 thus appear either to be allelic or closely linked. The implications for sunflower breeding are discussed.
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RFLP and RAPD mapping of the sunflower Pl1 locus for resistance to Plasmopara halstedii race 1
Theoretical and Applied Genetics, 1995Co-Authors: Said Mouzeyar, Felicity Vear, Denis Tourvieille De Labrouhe, Laurent Gentzbittel, P. Roeckel-drevet, J. Philippon, P. NicolasAbstract:The Pl1 locus in sunflower, Helianthus annuus L., conferring resistance to downy mildew, Plasmopara halstedii , race 1 has been located in linkage group 1 of the consensus RFLP map of the cultivated sunflower. Bulked segregant analyses were used on 135 plants of an F_2 progeny from a cross between a downy mildew susceptible line, GH, and RHA266, a line carrying Pl1 . Two RFLP markers and one RAPD marker linked to the Pl1 locus have been identified. The RFLP markers are located at 5.6 cM and 7.1 cM on either side of Pl1 . The RAPD marker is situated at 43.7 cM from Pl1 . The significance and applications of these markers in sunflower breeding are discussed.
Felicity Vear - One of the best experts on this subject based on the ideXlab platform.
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Sunflower resistance to multiple downy mildew pathotypes revealed by recognition of conserved effectors of the oomycete Plasmopara halstedii
Plant Journal, 2019Co-Authors: Yann Pecrix, David Rengel, Jerome Gouzy, Luis Fernando Buendia Martin, Charlotte Penouilh-suzette, Maude Marechaux, Ludovic Legrand, Olivier Bouchez, Ludovic Cottret, Felicity VearAbstract:Sunflower resistance to multiple downy mildew pathotypes revealed by recognition of conserved effectors of the oomycete Plasmopara halstedii
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A Method to Measure Aggressiveness of Plasmopara halstedii (Sunflower Downy Mildew)
Journal of Phytopathology, 2015Co-Authors: Nachaat Sakr, Mireille Ducher, Felicity Vear, Jeanne Tourvieille, Pascal Walser, Denis Tourvieille De LabrouheAbstract:For the first time, a method was used to measure aggressiveness of two Plasmopara halstedii races (100 and 710), the parasite causing sunflower downy mildew. Two sunflower lines showing different levels of quantitative resistance were used to measure two aggressiveness criteria: latent period and sporulation density. A strain of race 100 had a shorter latent period and greater sporulation density than a strain of race 710. The sunflower inbred line BT, rather susceptible in the field, presented a greater sporulation density and a shorter latent period than another inbred line FU, which shows greater resistance in the field. These results indicated that race 100 was more aggressive than race 710. The behaviour in the field of the two inbred lines was confirmed in the laboratory observations.
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The sunflower downy mildew pathogen Plasmopara halstedii
Molecular Plant Pathology, 2015Co-Authors: Quentin Gascuel, Felicity Vear, Marieclaude Boniface, Yves Martinez, Magalie Pichon, Laurence GodiardAbstract:Downy mildew of sunflower is caused by Plasmopara halstedii (Farlow) Berlese & de Toni. Plasmopara halstedii is an obligate biotrophic oomycete pathogen that attacks annual Helianthus species and cultivated sunflower, Helianthus annuus. Depending on the sunflower developmental stage at which infection occurs, the characteristic symptoms range from young seedling death, plant dwarfing, leaf bleaching and sporulation to the production of infertile flowers. Downy mildew attacks can have a great economic impact on sunflower crops, and several Pl resistance genes are present in cultivars to protect them against the disease. Nevertheless, some of these resistances have been overcome by the occurrence of novel isolates of the pathogen showing increased virulence. A better characterization of P.halstedii infection and dissemination mechanisms, and the identification of the molecular basis of the interaction with sunflower, is a prerequisite to efficiently fight this pathogen. This review summarizes what is currently known about P.halstedii, provides new insights into its infection cycle on resistant and susceptible sunflower lines using scanning electron and light microscopy imaging, and sheds light on the pathogenicity factors of P.halstedii obtained from recent molecular data. TaxonomyKingdom Stramenopila; Phylum Oomycota; Class Oomycetes; Order Peronosporales; Family Peronosporaceae; Genus Plasmopara; Species Plasmopara halstedii. Disease symptomsSunflower seedling damping off, dwarfing of the plant, bleaching of leaves, starting from veins, and visible white sporulation, initially on the lower side of cotyledons and leaves. Plasmopara halstedii infection may severely impact sunflower seed yield. Infection processIn spring, germination of overwintered sexual oospores leads to sunflower root infection. Intercellular hyphae are responsible for systemic plant colonization and the induction of disease symptoms. Under humid and fresh conditions, dissemination structures are produced by the pathogen on all plant organs to release asexual zoosporangia. These zoosporangia play an important role in pathogen dissemination, as they release motile zoospores that are responsible for leaf infections on neighbouring plants. Disease controlDisease control is obtained by both chemical seed treatment (mefenoxam) and the deployment of dominant major resistance genes, denoted Pl. However, the pathogen has developed fungicide resistance and has overcome some plant resistance genes. Research for more sustainable strategies based on the identification of the molecular basis of the interaction are in progress. Useful websites, , (soon available).
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The sunflower downy mildew pathogen Plasmopara halstedii.
Molecular plant pathology, 2014Co-Authors: Quentin Gascuel, Felicity Vear, Marieclaude Boniface, Yves Martinez, Magalie Pichon, Laurence GodiardAbstract:SUMMARY Downy mildew of sunflower is caused by Plasmopara halstedii (Farlow) Berlese & de Toni. Plasmopara halstedii is an obligate biotrophic oomycete pathogen that attacks annual Helianthus species and cultivated sunflower, Helianthus annuus. Depending on the sunflower developmental stage at which infection occurs, the characteristic symptoms range from young seedling death, plant dwarfing, leaf bleaching and sporulation to the production of infertile flowers. Downy mildew attacks can have a great economic impact on sunflower crops, and several Pl resistance genes are present in cultivars to protect them against the disease.Nevertheless, some of these resistances have been overcome by the occurrence of novel isolates of the pathogen showing increased virulence. A better characterization of P. halstedii infection and dissemination mechanisms,and the identification of the molecular basis of the interaction with sunflower, is a prerequisite to efficiently fight this pathogen. This review summarizes what is currently known about P. halstedii, provides new insights into its infection cycle on resistant and susceptible sunflower lines using scanning electron and light microscopy imaging, and sheds light on the pathogenicity factors of P. halstedii obtained from recent molecular data. Taxonomy: Kingdom Stramenopila; Phylum Oomycota; Class Oomycetes; Order Peronosporales; Family Peronosporaceae; Genus Plasmopara; Species Plasmopara halstedii. Disease symptoms: Sunflower seedling damping off, dwarfing of the plant, bleaching of leaves, starting from veins, and visible white sporulation, initially on the lower side of cotyledons and leaves. Plasmopara halstedii infection may severely impact sunflower seed yield. Infection process: In spring, germination of overwintered sexual oospores leads to sunflower root infection. Intercellular hyphae are responsible for systemic plant colonization and the induction of disease symptoms.Under humid and fresh conditions, dissemination structures are produced by the pathogen on all plant organs to release asexual zoosporangia.These zoosporangia play an important role in pathogen dissemination, as they release motile zoospores that are responsible for leaf infections on neighbouring plants. Disease control: Disease control is obtained by both chemical seed treatment (mefenoxam) and the deployment of dominant major resistance genes, denoted Pl. However, the pathogen has developed fungicide resistance and has overcome some plant resistance genes. Research for more sustainable strategies based on the identification of the molecular basis of the interaction are in progress. Useful websites: http://www.heliagene.org/HP, http://lipm -helianthus.toulouse.inra.fr/dokuwiki/doku.php?id=start, https:// www.heliagene.org/PlasmoparaSpecies (soon available).
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Quantitative resistance to downy mildew (Plasmopara halstedii) in sunflower (Helianthus annuus)
Euphytica, 2003Co-Authors: Denis Tourvieille De Labrouhe, Sylvie Roche, Pascal Walser, Fuschia Serre, Felicity VearAbstract:Downy mildew of sunflower, caused by the Oomycete, Plasmopara halstedii is at present controlled by major resistance genes. However, the pathogen has shown a considerable capacity for changes in virulence and these resistance genes are overcome only a few years after they have been introduced into new sunflower varieties. This paper presents research for quantitative, non-race-specific resistance independent of major genes. The reaction of cultivated sunflower genotypes to field attack by downy mildew was studied over 4 years in several environments and in the presence of the two most common races in France: 703 and 710. An experimental protocol with pre-emergence irrigation was developed, making it possible to observe downy mildew reaction whatever the weather conditions. Significant levels of partial resistance were observed in about 50 inbred sunflower lines among the 800 observed. These results suggest that it should be possible to select for non-race-specific downy mildew resistance and to include it in modern varieties. However, since this non-specific resistance is partial, it may be necessary to combine it with major gene resistance. Possible strategies are discussed to obtain durable resistance to downy mildew.
Otmar Spring - One of the best experts on this subject based on the ideXlab platform.
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Asexual Recombinants of Plasmopara halstedii Pathotypes from Dual Infection of Sunflower
PloS one, 2016Co-Authors: Otmar Spring, Reinhard ZipperAbstract:Genetically homogenous strains of Plasmopara halstedii differing in host specificity and fungicide tolerance were used to test the hypothesis that asexual genetic recombination occurs and may account for the high genotype diversity of this homothallic reproducing oomycete, which causes downy mildew in sunflower. Dual inoculation of sunflower seedlings with single zoospore strains of complementary infection characteristics caused sporulation under conditions where inoculation with each strain alone failed to infect. PCR-based investigation with strain-specific primers proved the presence of genetic traits from both progenitors in single sporangia collected from sporangiophores of such infections. Sister zoospores released from these sporangia revealed the genotype of the one or the other parental strain thus indicating heterokaryology of sporangia. Moreover, some zoospores showed amplification products of both parents, which suggests that the generally mononucleic spores derived from genetic recombination. The possibility of parasexual genetic exchange in the host-independent stage of infection and the evolutionary consequences are discussed.
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Occurrence and genetic diversity of the Plasmopara halstedii virus in sunflower downy mildew populations of the world.
Fungal biology, 2014Co-Authors: Wolfgang Grasse, Otmar SpringAbstract:Plasmopara halstedii virus (PhV) is a ss(+)RNA virus that exclusively occurs in the sunflower downy mildew pathogen Plasmopara halstedii, a biotrophic oomycete of severe economic impact. The virus origin and its genomic variability are unknown. A PCR-based screening of 128 samples of P. halstedii from five continents and up to 40 y old was conducted. PhV RNA was found in over 90 % of the isolates with no correlation to geographic origin or pathotype of its host. Sequence analyses of the two open reading frames (ORFs) revealed only 18 single nucleotide polymorphisms (SNPs) in 3873 nucleotides. The SNPs had no recognizable effect on the two encoded virus proteins. In 398 nucleotides of the untranslated regions (UTRs) of the RNA 2 strand eight additional SNPs and one short deletion was found. Modelling experiments revealed no effects of these variations on the secondary structure of the RNA. The results showed the presence of PhV in P. halstedii isolates of global origin and the existence of the virus since more than 40 y. The virus genome revealed a surprisingly low variation in both coding and noncoding parts. No sequence differences were correlated with host pathotype or geographic populations of the oomycete.
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Plasmopara halstedii virus causes hypovirulence in Plasmopara halstedii, the downy mildew pathogen of the sunflower.
Fungal genetics and biology : FG & B, 2013Co-Authors: Wolfgang Grasse, Reinhard Zipper, Maria Totska, Otmar SpringAbstract:Abstract Plasmopara halstedii virus (PhV) is an isometric virus recently found in the oomycete Plasmopara halstedii. The fully sequenced virus genome consists of two ss(+)RNA strands encoding for the virus polymerase and the coat protein, respectively. Most of previously screened field isolates of P. halstedii were found to harbor PhV, but effects of PhV on the pathogenicity and aggressiveness of the oomycete have not been investigated yet. To assess the influence of PhV on the infectivity of P. halstedii, virus-free isolates of the oomycete were searched for, cultivated on sunflower and used for single zoospore infection. Four genetically homogenous strains belonging to three different pathotypes (710, 730, 750) were established. Subcultures of each strain were successfully infected with PhV. This afforded pairs of isogenic strains with and without virus and allowed assessment of the pathogenicity (susceptibility to specific sunflower genotypes) and aggressiveness (intensity of infection, time scale and density of sporulation) in cultivation of sunflower. While no significant difference was found in the pathogenicity of P. halstedii strains with and without virus towards sunflower seedlings of different resistance (pathotype differentials), the aggressiveness of the oomycete was diminished by PhV. Compared to the virus-free strains, the time required for the first sporulation (latent period) increased by about 1 day post inoculation. Progression of the pathogen from the hypocotyl into the epicotyl of sunflower (systemic infection) was reduced by about one third in the presence of virus. In the virus containing strains, the average density of sporangia produced per cm2 cotyledon reached only 75% of the virus-free controls. In summary, the presence of PhV leads to hypovirulence effects by weakening the aggressiveness of P. halstedii.
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Identification of a novel Plasmopara halstedii elicitor protein combining de novo peptide sequencing algorithms and RACE-PCR.
Proteome Science, 2010Co-Authors: Stephan Jung, Frank Braendle, Otmar Spring, Claudia Fladerer, Johannes Madlung, Alfred NordheimAbstract:Background Often high-quality MS/MS spectra of tryptic peptides do not match to any database entry because of only partially sequenced genomes and therefore, protein identification requires de novo peptide sequencing. To achieve protein identification of the economically important but still unsequenced plant pathogenic oomycete Plasmopara halstedii, we first evaluated the performance of three different de novo peptide sequencing algorithms applied to a protein digests of standard proteins using a quadrupole TOF (QStar Pulsar i).
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Isozyme analysis of Plasmopara halstedii using cellulose-acetate gel electrophoresis
Plant Pathology, 2007Co-Authors: Hedvig Komjáti, Otmar Spring, J. Bakonyi, Ferenc VirányiAbstract:Isozyme analysis by cellulose-acetate gel electrophoresis was used for the first time on Plasmopara halstedii , the causal agent of sunflower downy mildew. Forty-five isolates originating from sunflower, cocklebur and Helianthus × laetiflorus were used, comprising 10 field isolates and 35 single-spore lines of an additional 30 field isolates representing 10 different virulence phenotypes. Sixteen isozyme systems were analysed, of which three, isocitrate dehydrogenase, malate dehydrogenase and phosphoglucomutase, resulted in clear, reproducible banding patterns and revealed some polymorphism among the isolates. Phosphoglucomutase differentiated two groups among the isolates collected from cultivated sunflower, while the other enzymes were polymorphic between isolates from the different hosts. Polymorphisms were not related to virulence phenotype.