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Poster

Session: Session 1 Presenting Authors at Posters (Odds)

P-119 - Homeodomain (HD) locus indicates a bipolar mating strategy for Ceratobasidium theobromae, causal agent of vascular-streak dieback of cocoa

Monday, July 14, 2025
13:30 - 15:15  
Location: Confex Hall 3
Management of diseases and emerging diseases

    Presenting Author(s)

  • PT

    Peri Tobias

    Dr
    University of Sydney
    Camperdown, NSW, AUSTRALIA

    • Author(s)

  • JD

    Jacob Downs (he/him/his)

    Postdoctoral Researcher
    University of Sydney
    Camperdown, New South Wales, Australia

  • SN

    Sylvie Nolf

    University of Sydney
    Camperdown, New South Wales, Australia

  • AP

    Agus Purwantara

    Mars Cocoa Research Station, Pangkep, Indonesia
    Pangkep, Sulawesi Selatan, Indonesia

  • JM

    Junaid Muhammad

    Lecturer
    Cocoa Research Center Faculty of Agriculture, Universitas Hasanuddin, Makassar, Indonesia
    Makassar, Sulawesi Selatan, Indonesia

  • EB

    Eirene Brugman

    Lecturer
    Cocoa Research Center Faculty of Agriculture, Universitas Hasanuddin, Makassar, Indonesia
    Makassar, Sulawesi Selatan, Indonesia

  • DG

    David Guest

    Professor of Plant Pathology
    University of Sydney
    Camperdown, New South Wales, Australia

The fastidious basidiomycete Ceratobasidium theobromae (P.H.B. Talbot & Keane) Samuels & Keane is a biotrophic pathogen that causes vascular-streak dieback (VSD) of Theobroma cacao L. (cocoa). The fungus is difficult to culture in vitro due its slow growth, and colonies are overrun by commensal fungi, hampering inoculation studies and Koch’s postulates. Recently, C. theobromae has been identified as the cause of Cassava Witches Broom Disease of Manihot esculenta Crantz (cassava) in southeast Asia and the Americas. The pathogen is also closely related to the causal agent of VSD in Cercis canadensis L. (redbud). These occurrences raise serious concerns that the pathogen is spreading globally. However, there is no evidence that isolates from cocoa are virulent on cassava or other hosts, or whether the species includes host-specific populations. Fungal homeodomain (HD) transcription factor mating-type loci are known to be polymorphic within the Basidiomycota. To understand diversity, and potential for sexual recombination we developed an assay for HD alleles with long amplicon sequences using Oxford Nanopore MinION. Interestingly, our work has shown that C. theobromae is homokaryotic, despite evidence of sexual recombination. We also determined that the HD locus is homozygous indicating a bipolar mating strategy, likely an evolutionary response to few available mating types. Our work shows that this assay can distinguish regional, and potentially host, strain variation.