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Thierry Rouxel - One of the best experts on this subject based on the ideXlab platform.
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one gene one name the avrlmj1 avirulence gene of Leptosphaeria maculans is avrlm5
Molecular Plant Pathology, 2018Co-Authors: Clémence Plissonneau, Thierry Rouxel, Angela P. Van De Wouw, Annemarie Chevre, Mariehelene BalesdentAbstract:Summary Leptosphaeria maculans, the causal agent of blackleg disease, interacts with Brassica napus (oilseed rape, canola) and other Brassica hosts, in a gene-for-gene manner. The avirulence gene AvrLmJ1 was previously cloned and shown to interact with an unidentified B. juncea resistance gene. In this study, we show that the AvrLmJ1 gene maps to the same position as the AvrLm5 locus. Furthermore, isolates complemented with the AvrLmJ1 locus confer avirulence towards B. juncea genotypes harbouring Rlm5. These findings demonstrate AvrLmJ1 is AvrLm5 and highlight the need for shared resources to characterise accurately avirulence and/or resistance genes. This article is protected by copyright. All rights reserved.
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life death and rebirth of avirulence effectors in a fungal pathogen of brassica crops Leptosphaeria maculans
New Phytologist, 2017Co-Authors: Thierry Rouxel, Mariehelene BalesdentAbstract:Contents 'Summary' 526 I. 'Introduction' 526 II. 'A new crop, novel resistance genes and ‘boom and bust’ cycles' 527 III. 'The ‘two-speed’ genome and specific genome environment of avirulence genes in Leptosphaeria maculans' 527 IV. 'Deletion and other types of inactivations: the easy way to go?' 529 V. 'Is extinction the common scheme?' 529 VI. '‘Rebirth’ of AvrLm3' 530 VII. 'Conclusions' 530 'Acknowledgements' 531 References 531 Summary In agricultural systems, major (R) genes for resistance in plants exert strong selection pressure on cognate/corresponding avirulence effector genes of phytopathogens. However, a complex interplay often exists between trade-offs linked to effector function and the need to escape R gene recognition. Here, using the Leptosphaeria maculans–oilseed rape pathosystem we review evolution of effectors submitted to multiple resistance gene selection. Characteristics of this pathosystem include a crop in which resistance genes have been deployed intensively resulting in ‘boom and bust’ cycles; a fungal pathogen with a high adaptive potential in which seven avirulence genes are cloned and for which population surveys have been coupled with molecular analysis of events responsible for virulence. The mode of evolution of avirulence genes, all located in dispensable parts of the ‘two-speed’ genome, is a highly dynamic gene-specific process. In some instances, avirulence genes are readily deleted under selection. However, others, even when located in the most plastic genome regions, undergo only limited point mutations or their avirulence phenotype is ‘camouflaged’ by another avirulence gene. Thus, while hundreds of effector genes are present, some effectors are likely to have an important and nonredundant function, suggesting functional redundancy and dispensability of effectors might not be the rule.
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Leptosphaeria maculans effectors involved in the oilseed rape systemic colonization.
2017Co-Authors: Julie Gervais, Thierry Rouxel, Clémence Plissonneau, Juliette Linglin, Michel Meyer, Karine Labadie, Cruaud Corinne, Benedicte Ollivier, Isabelle Fudal, Mariehelene BalesdentAbstract:The stem canker disease, caused by Leptosphaeria maculans, is one of the most devastating diseases of oilseed rape (canola). It colonizes the plant in two stages: a short and early colonisation stage corresponding to cotyledon or leaf colonisation, and a late colonisation stage during which the fungus colonises systemically and symptomlessly the plant during several months before stem canker appears. To date, determinants of the late colonisation stage remain poorly understood. By a transcriptomic approach, we previously identified two waves of effector candidate expression during the early and late colonisation stages (Gervais et al, 2016). The late effector candidates are located in gene-rich genomic regions, whereas the early effector genes are located in gene-poor regions of the genome. Among the late effector candidates identified, we selected 6 genes for further characterization. We created mutants silenced for these effector candidates. For one of these genes, its expression level correlated negatively with the size of the necrosis observed in the stem. The identification of new effector genes would contribute to the identification of new resistance genes specific to these effectors. To easily identify matching resistance genes in oilseed rape, we created transgenic isolates expressing these 6 late effectors at the early steps of infection to provide medium-throughput strategies to screen more efficiently different cultivars. Preliminary results indicate that some cultivars with adult resistance were more resistant to these transgenic isolates in cotyledon assays. With this approach, we also identified a cultivar carrying a specific resistance to one these 6 effector candidates. Reference Gervais, J., Plissonneau, C., Linglin, J., Meyer, M., Labadie, K., Cruaud, C., Fudal, I., Rouxel, T. and Balesdent, M.H. (2016) Different waves of effector genes with contrasted genomic location are expressed by Leptosphaeria maculans during cotyledon and stem colonization of oilseed rape. Mol. Plant Pathol.
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Clonal populations of Leptosphaeria maculans contaminating cabbage in Mexico
Plant Pathology, 2012Co-Authors: Azita Dilmaghani, Lilian Gout, Onésimo Moreno-rico, J. S. Dias, Laurent Coudard, N. Castillo-torres, M. H. Balesdent, Thierry RouxelAbstract:The race structure and genotypic diversity of four Leptosphaeria maculans populations isolated from Brassica oleracea (broccoli, cauliflower, cabbage, etc.) in central Mexico (Aguascalientes, Guanajuato and Zacatecas states) were analysed. Race structure was characterized by an unusually low diversity at three locations out of four. Fourteen minisatellite markers revealed a high proportion of repeated multilocus genotypes in these populations, combined with a significant linkage disequilibrium and strong clonal fraction (65‐87%). The occurrence of the mating-type idiomorphs always significantly departed from the 1:1 proportion expected in the case of random mating. Each population thus consists of a few (four to nine) multilocus genotypes which are specific to each location. These data strongly support the hypothesis of exclusive, or a high rate of, clonal multiplication. Comparison of cropping practices between B. oleracea and B. napus indicate that the shift in reproductive behaviour of the fungus is chiefly man-mediated.
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frequency of avirulence genes in Leptosphaeria maculans in western canada
Canadian Journal of Plant Pathology-revue Canadienne De Phytopathologie, 2010Co-Authors: H. R. Kutcher, Thierry Rouxel, S. R. Rimmer, M. H. Balesdent, Annemarie Chevre, Regine Delourme, H BrunAbstract:Abstract Changes in pathogenicity of populations of Leptosphaeria maculans, the cause of blackleg disease of canola and other Brassica spp., have been observed in western Canada. These changes in the population are believed to have resulted from the use of specific resistance (Rlm) genes in Brassica spp., many of which have only recently been identified. We determined the frequency of 10 avirulence alleles for 96 isolates of L. maculans collected between 1997 and 2005 from Alberta, Saskatchewan and Manitoba, Canada from infested canola stubble in field plots or farmers’ fields. Cotyledon interaction phenotypes were scored after inoculation of each isolate on a differential set of Brassica varieties or lines carrying the known resistance genes LepR3 and Rlm1 to Rlm10, except for Rlm8. The avirulence (AvrLm) alleles present in each isolate were inferred from the data. Due to the presence of confounding resistance genes in the host differentials, AvrLm1 and AvrLm2 could not be determined in nine of the isola...
Mariehelene Balesdent - One of the best experts on this subject based on the ideXlab platform.
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one gene one name the avrlmj1 avirulence gene of Leptosphaeria maculans is avrlm5
Molecular Plant Pathology, 2018Co-Authors: Clémence Plissonneau, Thierry Rouxel, Angela P. Van De Wouw, Annemarie Chevre, Mariehelene BalesdentAbstract:Summary Leptosphaeria maculans, the causal agent of blackleg disease, interacts with Brassica napus (oilseed rape, canola) and other Brassica hosts, in a gene-for-gene manner. The avirulence gene AvrLmJ1 was previously cloned and shown to interact with an unidentified B. juncea resistance gene. In this study, we show that the AvrLmJ1 gene maps to the same position as the AvrLm5 locus. Furthermore, isolates complemented with the AvrLmJ1 locus confer avirulence towards B. juncea genotypes harbouring Rlm5. These findings demonstrate AvrLmJ1 is AvrLm5 and highlight the need for shared resources to characterise accurately avirulence and/or resistance genes. This article is protected by copyright. All rights reserved.
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life death and rebirth of avirulence effectors in a fungal pathogen of brassica crops Leptosphaeria maculans
New Phytologist, 2017Co-Authors: Thierry Rouxel, Mariehelene BalesdentAbstract:Contents 'Summary' 526 I. 'Introduction' 526 II. 'A new crop, novel resistance genes and ‘boom and bust’ cycles' 527 III. 'The ‘two-speed’ genome and specific genome environment of avirulence genes in Leptosphaeria maculans' 527 IV. 'Deletion and other types of inactivations: the easy way to go?' 529 V. 'Is extinction the common scheme?' 529 VI. '‘Rebirth’ of AvrLm3' 530 VII. 'Conclusions' 530 'Acknowledgements' 531 References 531 Summary In agricultural systems, major (R) genes for resistance in plants exert strong selection pressure on cognate/corresponding avirulence effector genes of phytopathogens. However, a complex interplay often exists between trade-offs linked to effector function and the need to escape R gene recognition. Here, using the Leptosphaeria maculans–oilseed rape pathosystem we review evolution of effectors submitted to multiple resistance gene selection. Characteristics of this pathosystem include a crop in which resistance genes have been deployed intensively resulting in ‘boom and bust’ cycles; a fungal pathogen with a high adaptive potential in which seven avirulence genes are cloned and for which population surveys have been coupled with molecular analysis of events responsible for virulence. The mode of evolution of avirulence genes, all located in dispensable parts of the ‘two-speed’ genome, is a highly dynamic gene-specific process. In some instances, avirulence genes are readily deleted under selection. However, others, even when located in the most plastic genome regions, undergo only limited point mutations or their avirulence phenotype is ‘camouflaged’ by another avirulence gene. Thus, while hundreds of effector genes are present, some effectors are likely to have an important and nonredundant function, suggesting functional redundancy and dispensability of effectors might not be the rule.
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Leptosphaeria maculans effectors involved in the oilseed rape systemic colonization.
2017Co-Authors: Julie Gervais, Thierry Rouxel, Clémence Plissonneau, Juliette Linglin, Michel Meyer, Karine Labadie, Cruaud Corinne, Benedicte Ollivier, Isabelle Fudal, Mariehelene BalesdentAbstract:The stem canker disease, caused by Leptosphaeria maculans, is one of the most devastating diseases of oilseed rape (canola). It colonizes the plant in two stages: a short and early colonisation stage corresponding to cotyledon or leaf colonisation, and a late colonisation stage during which the fungus colonises systemically and symptomlessly the plant during several months before stem canker appears. To date, determinants of the late colonisation stage remain poorly understood. By a transcriptomic approach, we previously identified two waves of effector candidate expression during the early and late colonisation stages (Gervais et al, 2016). The late effector candidates are located in gene-rich genomic regions, whereas the early effector genes are located in gene-poor regions of the genome. Among the late effector candidates identified, we selected 6 genes for further characterization. We created mutants silenced for these effector candidates. For one of these genes, its expression level correlated negatively with the size of the necrosis observed in the stem. The identification of new effector genes would contribute to the identification of new resistance genes specific to these effectors. To easily identify matching resistance genes in oilseed rape, we created transgenic isolates expressing these 6 late effectors at the early steps of infection to provide medium-throughput strategies to screen more efficiently different cultivars. Preliminary results indicate that some cultivars with adult resistance were more resistant to these transgenic isolates in cotyledon assays. With this approach, we also identified a cultivar carrying a specific resistance to one these 6 effector candidates. Reference Gervais, J., Plissonneau, C., Linglin, J., Meyer, M., Labadie, K., Cruaud, C., Fudal, I., Rouxel, T. and Balesdent, M.H. (2016) Different waves of effector genes with contrasted genomic location are expressed by Leptosphaeria maculans during cotyledon and stem colonization of oilseed rape. Mol. Plant Pathol.
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migration patterns and changes in population biology associated with the worldwide spread of the oilseed rape pathogen Leptosphaeria maculans
Molecular Ecology, 2012Co-Authors: Azita Dilmaghani, Lilian Gout, Pierre Gladieux, Tatiana Giraud, Patrick C Brunner, A Stachowiak, Mariehelene BalesdentAbstract:Pathogen introductions into novel areas can lead to the emergence of new fungal diseases of plants. Understanding the origin, introduction pathways, possible changes in reproductive system and population size of fungal pathogens is essential in devising an integrated strategy for the control of these diseases. We used minisatellite markers to infer the worldwide invasion history of the fungal plant pathogen Leptosphaeria maculans, which causes stem canker (blackleg) of oilseed and vegetable brassicas. Clustering analyses partitioned genotypes into distinct populations corresponding to major geographic regions, along with two differentiated populations in Western Canada. Comparison of invasion scenarios using Approximate Bayesian Computation suggested an origin of the pathogen in the USA, the region where epidemics were first recorded, and independent introductions from there over the last few decades into Eastern Canada (Ontario), Europe and Australia. The population in Western Canada appeared to be founded from a source in Ontario and the population in Chile resulted from an admixture between multiple sources. A bottleneck was inferred for the introduction into Western Canada but not into Europe, Ontario or Australia. Clonality appeared high in Western Canada, possibly because environmental conditions there were less conducive to sexual reproduction. Leptosphaeria maculans is a model invasive pathogen with contrasting features in different regions: shallow population structure, high genetic variability and regular sexual recombination in some regions, by comparison with reduced genetic variability, high rates of asexual multiplication, strong population structure or admixture in others.
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The Lmgpi15 gene, encoding a component of the glycosylphosphatidylinositol anchor biosynthesis pathway, is required for morphogenesis and pathogenicity in Leptosphaeria maculans
New Phytologist, 2008Co-Authors: Estelle Remy, Mariehelene Balesdent, Michel Meyer, Françoise Blaise, Uwe K. Simon, Diana Kuhn, Mélanie Chabirand, Meritxell Riquelme, Thierry RouxelAbstract:Summary • Random insertional mutagenesis was used to investigate pathogenicity determinants in Leptosphaeria maculans. One tagged nonpathogenic mutant, termed m20, was analysed in detail here. • The mutant phenotype was investigated by microscopic analyses of infected plant tissues and in vitro growth assays. Complementation and silencing experiments were used to identify the altered gene. Its function was determined by bioinformatics analyses, cell biology experiments and functional studies. • The mutant was blocked at the invasive growth phase after an unaffected initial penetration stage, and displayed a reduced growth rate and an aberrant hyphal morphology in vitro. The T-DNA insertion occurred in the intergenic region between two head-to-tail genes, leading to a complex deregulation of their expression. The unique gene accounting for the mutant phenotype was suggested to be the orthologue of the poorly conserved Saccharomyces cerevisiae gpi15, which encodes for one component of the glycosylphosphatidylinositol (GPI) anchor biosynthesis pathway. Consistent with this predicted function, a functional translational fusion with the green fluorescent protein (GFP) was targeted to the endoplasmic reticulum. Moreover, the mutant exhibited an altered cell wall and addition of glucosamine relieved growth defects. • It is concluded that the GPI anchor biosynthetic pathway is required for morphogenesis, cell wall integrity and pathogenicity in Leptosphaeria maculans.
Barbara J Howlett - One of the best experts on this subject based on the ideXlab platform.
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Comprar Sustainable strategies for managing Brassica napus (oilseed rape) resistance to Leptosphaeria maculans (phoma stem canker) | Fitt, B.D.L. | 9781402045240 | Springer
2020Co-Authors: Bruce D.l. Fitt, Barbara J Howlett, Neal Evans, B.m. CookeAbstract:Tienda online donde Comprar Sustainable strategies for managing Brassica napus (oilseed rape) resistance to Leptosphaeria maculans (phoma stem canker) al precio 85,04 € de Fitt, B.D.L. | Evans, N. | Howlett, B.J. | Cooke, B.M., tienda de Libros de Medicina, Libros de Biologia - Zoologia
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Advances in understanding the Leptosphaeria maculans - Brassica pathosystem and their impact on disease management
Canadian Journal of Plant Pathology-revue Canadienne De Phytopathologie, 2019Co-Authors: Angela P. Van De Wouw, Barbara J HowlettAbstract:Recent advances in genomics have led to a greater understanding of blackleg disease of canola, caused by the fungus Leptosphaeria maculans. Genome sequences are available for several L. maculans is...
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next generation genome sequencing can be used to rapidly characterise sequences flanking t dna insertions in random insertional mutants of Leptosphaeria maculans
Fungal biology and biotechnology, 2014Co-Authors: Kylie Chambers, Barbara J Howlett, Angela P. Van De Wouw, Manuel Zander, J R Batley, Rohan Gt Lowe, Candace E. ElliottAbstract:Banks of mutants with random insertions of T-DNA from Agrobacterium tumefaciens are often used in forward genetics approaches to identify phenotypes of interest. Upon identification of mutants of interest, the flanking sequences of the inserted T-DNA must be identified so that the mutated gene can be characterised. However, for many fungi, this task is not trivial as widely used PCR-based methods such as thermal asymmetric interlaced polymerase chain reaction (TAIL-PCR) are not successful. Next-generation Illumina sequencing was used to locate T-DNA insertion sites in four mutants of Leptosphaeria maculans, a fungal plant pathogen. Sequence reads of up to 150 bp and coverage ranging from 6 to 24 times, were sufficient for identification of insertion sites in all mutants. All T-DNA border sequences were truncated to different extents. Additionally, next-generation sequencing revealed chromosomal rearrangements associated with the insertion in one of the mutants. Next-generation sequencing is a cost-effective and rapid method of identifying sites of T-DNA insertions, and associated genomic rearrangements in Leptosphaeria maculans and potentially in other fungal species.
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The cross-pathway control system regulates production of the secondary metabolite toxin, sirodesmin PL, in the ascomycete, Leptosphaeria maculans
BMC Microbiology, 2011Co-Authors: Candace E. Elliott, Renee S. Jarvis, Barbara J HowlettAbstract:Background Sirodesmin PL is a secondary metabolite toxin made by the ascomycetous plant pathogen, Leptosphaeria maculans. The sirodesmin biosynthetic genes are clustered in the genome. The key genes are a non-ribosomal peptide synthetase, sirP, and a pathway-specific transcription factor, sirZ. Little is known about regulation of sirodesmin production.
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determining frequencies of avirulent alleles in airborne Leptosphaeria maculans inoculum using quantitative pcr
Plant Pathology, 2010Co-Authors: A P Van De Wouw, Barbara J Howlett, Bruce D.l. Fitt, J F Stonard, J S West, S D AtkinsAbstract:Phoma stem canker (blackleg disease) of Brassica napus (oilseed rape, canola) is caused by the fungus Leptosphaeria maculans. Frequencies of avirulent alleles for loci where virulence can be associated with gene deletion (AvrLm1 and AvrLm6) were determined in samples of L. maculans airborne ascospore inoculum using quantitative PCR. The accuracy, reproducibility and limitations of detection were determined. Changes in the frequency of avirulent alleles were determined for the 2006/2007, 2007/2008 and 2008/2009 growing seasons for winter oilseed rape in the UK. The frequency of AvrLm1 remained small (between 9% and 16%), whilst the frequency of AvrLm6 fluctuated between 35% and 66%. Estimation of frequencies of avirulent alleles in airborne pathogen inoculum gives an efficient and unbiased method to assess the potential of crop cultivars with corresponding resistance genes being at risk of disease.
S. R. Rimmer - One of the best experts on this subject based on the ideXlab platform.
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frequency of avirulence genes in Leptosphaeria maculans in western canada
Canadian Journal of Plant Pathology-revue Canadienne De Phytopathologie, 2010Co-Authors: H. R. Kutcher, Thierry Rouxel, S. R. Rimmer, M. H. Balesdent, Annemarie Chevre, Regine Delourme, H BrunAbstract:Abstract Changes in pathogenicity of populations of Leptosphaeria maculans, the cause of blackleg disease of canola and other Brassica spp., have been observed in western Canada. These changes in the population are believed to have resulted from the use of specific resistance (Rlm) genes in Brassica spp., many of which have only recently been identified. We determined the frequency of 10 avirulence alleles for 96 isolates of L. maculans collected between 1997 and 2005 from Alberta, Saskatchewan and Manitoba, Canada from infested canola stubble in field plots or farmers’ fields. Cotyledon interaction phenotypes were scored after inoculation of each isolate on a differential set of Brassica varieties or lines carrying the known resistance genes LepR3 and Rlm1 to Rlm10, except for Rlm8. The avirulence (AvrLm) alleles present in each isolate were inferred from the data. Due to the presence of confounding resistance genes in the host differentials, AvrLm1 and AvrLm2 could not be determined in nine of the isola...
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Analysis of EST Libraries from Leptosphaeria maculans and Blackleg Infected Brassica napus
The Open Mycology Journal, 2008Co-Authors: J.a. Christianson, S. R. Rimmer, Allen G. Good, Derek J. LydiateAbstract:The ascomycete Leptosphaeria maculans is the causal agent of blackleg of crucifers. cDNA libraries were constructed and partially sequenced to increase the amount of L. maculans sequence data available and to survey genes expressed during pathogenesis. Two libraries were built, one from cultured mycelia (LM) and one from Brassica napus leaf tissue infected with L. maculans (ILS). A total of 741 expressed sequence tags (ESTs) were obtained from the LM library, and 1284 were obtained from the ILS library. The vast majority of the ESTs obtained from the ILS library appear to originate from B. napus (70-81% depending on the identification method). Various methods for determining sequence origin in mixed libraries were compared. cDNAs with a putative role in pathogenesis were identified from the ILS library. These and other cDNAs of interest from the LM library are discussed.
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Pathogenic variability of Leptosphaeria maculans in western Canada
Canadian Journal of Plant Pathology-revue Canadienne De Phytopathologie, 2007Co-Authors: H. R. Kutcher, M. Keri, D. L. Mclaren, S. R. RimmerAbstract:Blackleg, caused by Leptosphaeria maculans, is one of the most destructive diseases in Brassica species in Canada and worldwide. Information on variability in virulence is essential for the development of effective control strategies. To characterize the virulence structure of the L. maculans population in western Canada, 262 Leptosphaeria isolates collected from Brassica napus and Brassica rapa (canola) fields between 1998 and 2000 were evaluated for virulence on two sets of B. napus differentials, each with three lines. The isolates were classified into two Leptosphaeria species based on the differential reaction on ‘Westar’. Sixty-nine isolates (28.3%) avirulent on ‘Westar’ were identified as Leptosphaeria biglobosa and 175 isolates (71.3%) virulent on ‘Westar’ as L. maculans. The L. maculans isolates were classified into three pathogenicity groups (PGs) based on their differential reactions to lines in set A. Eighteen of the field isolates were not classifiable because of inconsistent differential rea...
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Mapping genes for resistance to Leptosphaeria maculans in Brassica juncea.
Genome, 2006Co-Authors: J.a. Christianson, S. R. Rimmer, Allen G. Good, Derek J. LydiateAbstract:Blackleg disease of crucifers, caused by the fungus Leptosphaeria maculans, is a major concern to oilseed rape producers worldwide. Brassica species containing the B genome have high levels of resistance to blackleg. Brassica juncea F2 and first-backcross (B1) populations segregating for resistance to a PG2 isolate of L. maculans were created. Segregation for resistance to L. maculans in these populations suggested that resistance was controlled by two independent genes, one dominant and one recessive in nature. A map of the B. juncea genome was constructed using segregation in the F2 population of a combination of restriction fragment length polymorphism (RFLP) and microsatel lite markers. The B. juncea map consisted of 325 loci and was aligned with previous maps of the Brassica A and B genomes. The gene controlling dominant resistance to L. maculans was positioned on linkage group J13 based on segregation for resistance in the F2 population. This position was confirmed in the B1 population in which the ...
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World-Wide Importance of Phoma Stem Canker (Leptosphaeria maculans and L. biglobosa) on Oilseed Rape (Brassica napus)
European Journal of Plant Pathology, 2006Co-Authors: B. D. L. Fitt, H Brun, M. J. Barbetti, S. R. RimmerAbstract:Phoma stem canker is an internationally important disease of oilseed rape ( Brassica napus , canola, rapeseed), causing serious losses in Europe, Australia and North America. UK losses of €56M per season are estimated using national disease survey data and a yield loss formula. Phoma stem canker pathogen populations comprise two main species, Leptosphaeria maculans , associated with damaging stem base cankers, and Leptosphaeria biglobosa , often associated with less damaging upper stem lesions. Both major gene and quantitative trait loci mediated resistance to L. maculans have been identified in B. napus , but little is known about resistance to L. biglobosa. Leptosphaeria maculans , which has spread into areas in North America and eastern Europe where only L. biglobosa was previously identified, now poses a threat to large areas of oilseed rape production in Asia. Epidemics are initiated by air-borne ascospores; major gene resistance to initial infection by L. maculans operates in the leaf lamina of B. napus . It is not clear whether the quantitative trait loci involved in the resistance to the pathogen that can be assessed only at the end of the season operate in the leaf petioles or stems. In countries where serious phoma stem canker epidemics occur, a minimum standard for resistance to L. maculans is included in national systems for registration of cultivars. This review provides a background to a series of papers on improving strategies for managing B. napus resistance to L. maculans , which is a model system for studying genetic interactions between hemi-biotrophic pathogens and their hosts.
M. H. Balesdent - One of the best experts on this subject based on the ideXlab platform.
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Clonal populations of Leptosphaeria maculans contaminating cabbage in Mexico
Plant Pathology, 2012Co-Authors: Azita Dilmaghani, Lilian Gout, Onésimo Moreno-rico, J. S. Dias, Laurent Coudard, N. Castillo-torres, M. H. Balesdent, Thierry RouxelAbstract:The race structure and genotypic diversity of four Leptosphaeria maculans populations isolated from Brassica oleracea (broccoli, cauliflower, cabbage, etc.) in central Mexico (Aguascalientes, Guanajuato and Zacatecas states) were analysed. Race structure was characterized by an unusually low diversity at three locations out of four. Fourteen minisatellite markers revealed a high proportion of repeated multilocus genotypes in these populations, combined with a significant linkage disequilibrium and strong clonal fraction (65‐87%). The occurrence of the mating-type idiomorphs always significantly departed from the 1:1 proportion expected in the case of random mating. Each population thus consists of a few (four to nine) multilocus genotypes which are specific to each location. These data strongly support the hypothesis of exclusive, or a high rate of, clonal multiplication. Comparison of cropping practices between B. oleracea and B. napus indicate that the shift in reproductive behaviour of the fungus is chiefly man-mediated.
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frequency of avirulence genes in Leptosphaeria maculans in western canada
Canadian Journal of Plant Pathology-revue Canadienne De Phytopathologie, 2010Co-Authors: H. R. Kutcher, Thierry Rouxel, S. R. Rimmer, M. H. Balesdent, Annemarie Chevre, Regine Delourme, H BrunAbstract:Abstract Changes in pathogenicity of populations of Leptosphaeria maculans, the cause of blackleg disease of canola and other Brassica spp., have been observed in western Canada. These changes in the population are believed to have resulted from the use of specific resistance (Rlm) genes in Brassica spp., many of which have only recently been identified. We determined the frequency of 10 avirulence alleles for 96 isolates of L. maculans collected between 1997 and 2005 from Alberta, Saskatchewan and Manitoba, Canada from infested canola stubble in field plots or farmers’ fields. Cotyledon interaction phenotypes were scored after inoculation of each isolate on a differential set of Brassica varieties or lines carrying the known resistance genes LepR3 and Rlm1 to Rlm10, except for Rlm8. The avirulence (AvrLm) alleles present in each isolate were inferred from the data. Due to the presence of confounding resistance genes in the host differentials, AvrLm1 and AvrLm2 could not be determined in nine of the isola...
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a cluster of major specific resistance genes to Leptosphaeria maculans in brassica napus
Phytopathology, 2004Co-Authors: Regine Delourme, Thierry Rouxel, H Brun, M Renard, M L Piletnayel, M Archipiano, R Horvais, X Tanguy, M. H. BalesdentAbstract:ABSTRACT Two types of genetic resistance to Leptosphaeria maculans usually are distinguished in Brassica napus: qualitative, total resistance expressed at the seedling stage and quantitative, partial resistance expressed at the adult plant stage. The latter is under the control of many genetic factors that have been mapped through quantitative trait loci (QTL) studies using ‘Darmor’ resistance. The former usually is ascribed to race-specific resistance controlled by single resistance to L. maculans (Rlm) genes. Three B. napus-originating specific Rlm genes (Rlm1, Rlm2, and Rlm4) previously were characterized. Here, we report on the genetic identification of two novel resistance genes, Rlm3 and Rlm7, corresponding to the avirulence genes AvrLm3 and AvrLm7. The identification of a novel L. maculans- B. napus specific interaction allowed the detection of another putative new specific resistance gene, Rlm9. The resistance genes were mapped in two genomic regions on LG10 and LG16 linkage groups. A cluster of f...
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new avirulence genes in the phytopathogenic fungus Leptosphaeria maculans
Phytopathology, 2002Co-Authors: M. H. Balesdent, Agnes Attard, Marieline Kuhn, Thierry RouxelAbstract:ABSTRACT Leptosphaeria maculans, the causal agent of stem canker of oilseed rape (Brassica napus), develops gene-for-gene interactions with oilseed rape, and four L. maculans avirulence (AVR) genes (AvrLm1, AvrLm2, AvrLm4, and alm1) were previously genetically characterized. Based on the analysis of progeny of numerous in vitro crosses between L. maculans isolates showing either already characterized or new differential interactions, this work aims to provide an overview of the AVR genes that may specify incompatibility toward B. napus and the related species B. juncea and B. rapa. Two novel differential interactions were thus identified between L. maculans and B. napus genotypes, one of them corresponding to a complete resistance to European races of L. maculans. In both cases, a single gene control of avirulence was established (genes AvrLm3 and AvrLm7). Similarly, a single gene control of avirulence toward a B. rapa genotype, also resistant to European L. maculans isolates, was demonstrated (gene AvrLm...
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Genetic characterization of AvrLm1, the first avirulence gene of Leptosphaeria maculans
Phytopathology, 1995Co-Authors: D. Ansan-melayah, M. H. Balesdent, Marc Buée, Thierry RouxelAbstract:Specific interactions of the fungal pathogen Leptosphaeria maculans with Brassica napus cultivars were observed when the cultivars were inoculated with isolates belonging to pathogenicity groups (PG) PG3 and PG4. PG3 isolates induced resistance responses on cotyledons or leaves of cv. Quinta, whereas PG4 isolates caused sporulating lesions on this cultivar. In contrast, both pathotypes caused disease symptoms on cvs. Westar and Glacier. The genetic basis of cultivar specificity was studied using tetrad analysis after in vitro crosses between one PG3 and one PG4 isolate. For the genetic study, the use of random amplified polymorphic DNA (RAPD) as genetic markers was assessed. Of 61 primers, 10 generated reproducible polymorphisms. Of these, 9 generated 18 RAPD markers displaying a 2 :2 segregation ratio within the 10 analyzed tetrads. A 2 :2 segregation ratio for avirulence/virulence to cv. Quinta also was observed in the progeny. Consequently, the single genetic locus controlling cultivar specificity on Quinta was considered the first avirulence gene described in L. maculans and was designated AvrLM1.