scholarly journals Analysis of Leptosphaeria maculans Race Structure in a Worldwide Collection of Isolates

2005 ◽  
Vol 95 (9) ◽  
pp. 1061-1071 ◽  
Author(s):  
M. H. Balesdent ◽  
M. J. Barbetti ◽  
Hua Li ◽  
K. Sivasithamparam ◽  
L. Gout ◽  
...  
Keyword(s):  
Resistance Gene ◽  
Oilseed Rape ◽  
Leptosphaeria Maculans ◽  
Stem Canker ◽  
Allele Frequencies ◽  
Gene Interactions ◽  
Avr Gene ◽  
Avr Genes ◽  
Structure Diversity

Leptosphaeria maculans, the causal agent of stem canker of oilseed rape, develops gene-for-gene interactions with its hosts. To date, eight L. maculans avirulence (Avr) genes, AvrLm1 to AvrLm8, have been genetically characterized. An additional Avr gene, AvrLm9, that interacts with the resistance gene Rlm9, was genetically characterized here following in vitro crosses of the pathogen. A worldwide collection of 63 isolates, including the International Blackleg of Crucifers Network collection, was genotyped at these nine Avr loci. In a first step, isolates were classified into pathogenicity groups (PGs) using two published differential sets. This analysis revealed geographical disparities as regards the proportion of each PG. Genotyping of isolates at all Avr loci confirmed the disparities between continents, in terms of Avr allele frequencies, particularly for AvrLm2, AvrLm3, AvrLm7, AvrLm8, and AvrLm9, or in terms of race structure, diversity, and complexity. Twenty-six distinct races were identified in the collection. A larger number of races (n = 18) was found in Australia than in Europe (n = 8). Mean number of virulence alleles per isolate was also higher in Australia (5.11 virulence alleles) than in Europe (4.33) and Canada (3.46). Due to the diversity of populations of L. maculans evidenced here at the race level, a new, open terminology is proposed for L. maculans race designation, indicating all Avr loci for which the isolate is avirulent.

scholarly journals Genetic Control and Host Range of Avirulence Toward Brassica napus Cultivars Quinta and Jet Neuf in Leptosphaeria maculans

2001 ◽  
Vol 91 (1) ◽  
pp. 70-76 ◽  
Author(s):  
M. H. Balesdent ◽  
A. Attard ◽  
D. Ansan-Melayah ◽  
R. Delourme ◽  
M. Renard ◽  
...  
Keyword(s):  
Brassica Napus ◽  
Resistance Gene ◽  
Single Gene ◽  
Leptosphaeria Maculans ◽  
Avirulence Gene ◽  
Gene Interactions ◽  
Deleterious Gene ◽  
Or Genes ◽  
Avr Gene ◽  
Avr Genes

Leptosphaeria maculans causes blackleg of oilseed rape. Gene-for-gene interactions between race PG3 and Brassica napus cv. Quinta were related to interaction between the fungal avirulence (Avr) gene AvrLm1 and the corresponding resistance gene Rlm1. AvrLm1 isolates were aviru-lent on cvs. Doublol, Vivol, Columbus, and Capitol, and no recombinant phenotypes were observed in the progeny of two AvrLm1 × avrLm1 crosses, suggesting that all of these cultivars may possess Rlm1 or genes displaying the same recognition spectrum, or that a cluster of Avr genes is present at the Avrlm1 locus. In one cross, segregation distortion was observed at the AvrLm1 locus that could be explained by interaction between AvrLm1 and one unlinked deleterious gene, termed Del1. Incompatibility toward cvs. Jet Neuf and Darmor.bzh was governed by a single gene, unlinked to AvrLm1 or Del1. This avirulence gene was termed AvrLm4. Preliminary plant genetic analysis suggested the occurrence of a corresponding dominant resistance gene, termed Rlm4, present in the Quinta line analyzed and linked to Rlm1.

scholarly journals New Avirulence Genes in the Phytopathogenic Fungus Leptosphaeria maculans

2002 ◽  
Vol 92 (10) ◽  
pp. 1122-1133 ◽  
Author(s):  
M. H. Balesdent ◽  
A. Attard ◽  
M. L. Kühn ◽  
T. Rouxel
Keyword(s):  
Gene Cluster ◽  
Oilseed Rape ◽  
Single Gene ◽  
Leptosphaeria Maculans ◽  
Phytopathogenic Fungus ◽  
Gene Control ◽  
Avirulence Genes ◽  
Avr Gene ◽  
Avr Genes

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 AvrLm8). Finally, a digenic control of avirulence toward B. juncea was established (genes AvrLm5 and AvrLm6). Linkage analyses demonstrated that at least four unlinked L. maculans genomic regions, including at least one AVR gene cluster (AvrLm1-AvrLm2-AvrLm6), are involved in host specificity. The AvrLm3-AvrLm4-AvrLm7 region may correspond either to a second AVR gene cluster or to a multiallelic AVR gene.

scholarly journals Careful deployment of oilseed rape crops with Rlm6 resistance gene against L. maculans is recommended to prevent the loss of efficacy of this resistance gene in French condiment mustard

2018 ◽  
Author(s):  
L. Bousset ◽  
M. Ermel ◽  
R. Delourme
Keyword(s):  
Disease Control ◽  
Resistance Gene ◽  
Oilseed Rape ◽  
Resistance Genes ◽  
Leptosphaeria Maculans ◽  
Stem Canker ◽  
Negative Consequences ◽  
Phoma Stem Canker ◽  
Breeding Lines ◽  
Additional Resistance

AbstractBreeding varieties for increased disease resistance is a major means to control epidemics. However, the deployment of resistance genes through space and time drives the genetic composition of the pathogen population, with predictable changes in pathotype frequencies. In France, Leptosphaeria maculans causes disease on Brassica napus oilseed rape crops but not on B. juncea condiment mustard. Prior to the deployment of winter B. napus varieties with Rlm6 resistance gene introduced from B. juncea, the aim of our study was to investigate if this deployment could impact disease control in condiment mustard. We assessed the presence of resistance genes against phoma stem canker in a set of current French B. juncea varieties and breeding lines. Rlm6 was detected in all the 12 condiment mustard varieties. Rlm5 was also detected in 8 varieties. No additional resistance genes were detected with the set of isolates used. Because frequency of isolates virulent on Rlm6 is very low, these results indicate that Rlm6 gene is a major component of disease control in the French B. juncea mustards tested. Using Rlm6 in oilseed rape varieties will very likely induce an increase in frequency of Rlm6 virulent isolates. This raises the acute concern of a wise deployment of oilseed rape around the condiment mustard growing area. Scientific knowledge on adaptation dynamics, spatial segregation of crops and cooperation between actors is currently available in order to mitigate the risk and advert negative consequences of the introduction of Rlm6 resistance gene in oilseed rape varieties.

scholarly journals Occurrence of a New Subclade of Leptosphaeria biglobosa in Western Australia

2008 ◽  
Vol 98 (3) ◽  
pp. 321-329 ◽  
Author(s):  
L. Vincenot ◽  
M. H. Balesdent ◽  
H. Li ◽  
M. J. Barbetti ◽  
K. Sivasithamparam ◽  
...  
Keyword(s):  
Oilseed Rape ◽  
Mating Type ◽  
Western Australia ◽  
Leptosphaeria Maculans ◽  
Stem Canker ◽  
Tubulin Genes ◽  
Wide Scale ◽  
Scale Characterization ◽  
Leptosphaeria Biglobosa ◽  
Β Tubulin

Stem canker of crucifers is caused by an ascomycete species complex comprising of two main species, Leptosphaeria maculans and L. biglobosa. These are composed of at least seven distinct subclades based on biochemical data or on sequences of internal transcribed spacer (ITS), the mating type MAT1-2 or fragments of actin or β-tubulin genes. In the course of a wide-scale characterization of the race structure of L. maculans from Western Australia, a few isolates from two locations failed to amplify specific sequences of L. maculans, i.e., the mating-type or minisatellite alleles. Based on both pathogenicity tests and ITS size, these isolates were classified as belonging to the L. biglobosa species. Parsimony and distance analyses performed on ITS, actin and β-tubulin sequences revealed that these isolates formed a new L. biglobosa subclade, more related to the Canadian L. biglobosa ‘canadensis’ subclade than to the L. biglobosa ‘australensis’ isolates previously described in Australia (Victoria). They are termed here as L. biglobosa ‘occiaustralensis’. These isolates were mainly recovered from resistant oilseed rape cultivars that included the Brassica rapa sp. sylvestris-derived resistance source, but not from the susceptible cv. Westar. The pathogenicity of L. biglobosa ‘occiaustralensis’ to cotyledons of most oilseed rape genotypes was higher than that of L. biglobosa ‘canadensis’ or L. biglobosa ‘australensis’ isolates.

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