A new set of international Leptosphaeria maculans isolates as a resource for elucidation of the basis and evolution of blackleg disease on Brassica napus

Abstract

A collection of isolates of the fungi Leptosphaeria maculans and L. biglobosa, which cause blackleg disease on Brassica napus (canola/oilseed rape) and other Brassicaceae species, was assembled to represent the global diversity of these pathogens and a resource for international research. The collection consists of 226 isolates (205 L. maculans and 21 L. biglobosa) from 11 countries. The genomes of all 205 L. maculans isolates were sequenced, and the distribution and identity of avirulence gene alleles were determined based on genotypic information and phenotypic reactions on B. napus lines that hosted specific resistance genes. Whilst the frequencies of some avirulence alleles were consistent across each of the regions, others differed dramatically, potentially reflecting the canola/oilseed rape cultivars grown in those countries. Analyses of the single‐nucleotide polymorphism (SNP) diversity within these L. maculans isolates revealed geographical separation of the populations. This "open access" resource provides a standardized set of isolates that can be used to define the basis for how these fungal pathogens cause disease, and as a tool for discovery of new resistance traits in Brassica species.

MPSeqM, a tool combining multiplex PCR and high-throughput sequencing to study the polymorphism of eightLeptosphaeria maculansavirulence genes and its application to field surveys in France

“…As already observed following the sequencing of individual isolates (Gautier et al, 2023;Van de Wouw et al, 2023), a high level of polymorphism was detected for AvrLmS. Forty-one alleles were detected here, with 27 new alleles compared to previous data (Gautier et al, 2023).…”

“…In most cases, however, the deletion is not the only mutational event in virulent isolates, and deletions may be rare or even never observed for some AvrLm genes (Gautier et al, 2023, Van de Wouw et al, 2023.…”

“…Similarly, sequences of avirulence genes in an international collection of 205 L. maculans isolates were recently published (Van de Wouw et al, 2023). Although powerful and exhaustive, such an approach cannot be performed on hundreds of isolates every year.…”

“…A quantitative PCR assay was developed to quantify the proportion of deleted isolates for AvrLm1 , relative to the ITS (Van de Wouw et al, 2010). In most cases, however, the deletion is not the only mutational event in virulent isolates, and deletions may be rare or even never observed for some AvrLm genes (Gautier et al, 2023, Van de Wouw et al, 2023).…”

“…For instance, Chen et al (2020) studied the polymorphism in nine avirulence genes following the WGS of 162 Canadian isolates. Similarly, sequences of avirulence genes in an international collection of 205 L. maculans isolates were recently published (Van de Wouw et al, 2023). Although powerful and exhaustive, such an approach cannot be performed on hundreds of isolates every year.…”