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

M H Balesdent, M J Barbetti, Hua Li

    Phytopathology
    |October 24, 2008
    PubMed

    Insights

    Leptosphaeria maculans avirulence (Avr) genes show significant global variation. Researchers propose a new open nomenclature for L. maculans races based on these gene variations.

    Area of Science:

    • Plant pathology
    • Molecular genetics
    • Agricultural science

    Background:

    • Leptosphaeria maculans causes oilseed rape stem canker through gene-for-gene interactions.
    • Eight avirulence (Avr) genes (AvrLm1-AvrLm8) were previously characterized.
    • A ninth Avr gene, AvrLm9, interacting with resistance gene Rlm9, is now genetically characterized.

    Purpose of the Study:

    • To genetically characterize AvrLm9.
    • To genotype a global collection of L. maculans isolates at nine Avr loci.
    • To analyze geographical disparities in pathogenicity groups, race structure, and diversity.

    Main Methods:

    • In vitro crosses were used to genetically characterize AvrLm9.
    • Sixty-three L. maculans isolates were genotyped at nine Avr loci.
    • Isolates were classified into pathogenicity groups using differential sets.

    Main Results:

    • Geographical disparities in pathogenicity group proportions were observed.
    • Significant differences in Avr allele frequencies and race structure were confirmed between continents, especially for AvrLm2, AvrLm3, AvrLm7, AvrLm8, and AvrLm9.
    • Twenty-six distinct races were identified, with Australia having more races (18) than Europe (8).
    • Australia showed a higher mean number of virulence alleles per isolate (5.11) compared to Europe (4.33) and Canada (3.46).

    Conclusions:

    • Global populations of L. maculans exhibit significant diversity at the race level.
    • A new, open terminology is proposed for designating L. maculans races, detailing avirulence at all identified Avr loci.
    • Understanding this diversity is crucial for managing stem canker in oilseed rape.

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