Abstract
The ophiostomatoid fungi are an assemblage of ascomycetes which are arguably best-known for their associations with bark and ambrosia beetles (Curculonidae) and blue stain (sap stain) of many economically important tree species. These fungi are considered a significant threat to coniferous forests, which has resulted in numerous studies characterising the diversity of bark beetles and their ophiostomatoid associates globally. The diversity of ophiostomatoid fungi present in Australian pine plantations, however, remains largely undetermined. The aims of this study were therefore to reconsider the diversity of ophiostomatoid fungi associated with Pinus in Australia, and to establish the baseline of expected taxa found within these plantation ecosystems. To achieve this, we reviewed Australian plant pathogen reference collections, and analysed samples collected during forest health surveillance programs from the major pine growing regions in south-eastern Australia. In total, 135 ophiostomatoid isolates (15 from reference collections and 120 collected during the current study) were assessed using morphological identification and ITS screening which putatively distinguished 15 taxonomic groups. Whole genome sequencing (WGS) of representative isolates from each taxon was performed to obtain high-quality sequence data for multi-locus phylogenetic analysis. Our results revealed a greater than expected diversity, expanding the status of ophiostomatoid fungi associated with Pinus in Australia to include 14 species from six genera in the Ophiostomatales and a single species residing in the Microascales. While most of these were already known to science, our study includes seven first records for Australia and the description of one new species, Graphilbum ipis-grandicollis sp. nov.. This study also provides an early example of whole genome sequencing (WGS) approaches replacing traditional PCR-based methods for taxonomic surveys. This not only allowed for robust multi-locus sequence extraction during taxonomic assessment, but also permitted the rapid establishment of a curated genomic database for ophiostomatoid fungi which will continue to aid in the development of improved diagnostic resources and capabilities for Australian biosecurity.
Highlights
Fungi within Ophiostomatales and Microascales are best known for their associations with arthropod vectors and include examples of some of the most devastating fungalinsect symbioses known to plant pathologists over the past century (Fisher et al 2012; Wingfield et al 2017b; Trollip et al IMA Fungus (2021) 12:24Brasier and Webber 2019)
In order to achieve this, we looked to: (1) review all available ophiostomatoid reference material previously reported from pine and lodged in Australian plant pathogen reference collections; (2) survey the ophiostomatoid fungi found in pine plantations during the 2019–2020 forest health surveillance period; and (3) use whole genome sequencing (WGS) of representative taxa to establish a curated database for improved molecular diagnostics of ophiostomatoid fungi for Australian biosecurity
Living cultures were recovered from the Victorian Plant Pathology Herbarium (VPRI) and the New South Wales (NSW) Plant Pathology and Mycology Herbarium (DAR) following database searches using the currently accepted nomenclature (Seifert et al 2013) and all putative synonyms (MycoBank Database, www.mycobank.org; Species Fungorum, www.speciesfungorum.org) of ophiostomatoid fungi that were recorded in the respective Australian collections and associated with Pinus
Summary
Fungi within Ophiostomatales and Microascales are best known for their associations with arthropod vectors and include examples of some of the most devastating fungalinsect symbioses known to plant pathologists over the past century (Fisher et al 2012; Wingfield et al 2017b; Trollip et al IMA Fungus (2021) 12:24Brasier and Webber 2019). Despite being formally recognised as two distinct orders in the Sordariomycetes, species belonging to Ophiostomatales and Microascales share a long and complicated taxonomic history and are collectively referred to as the ophiostomatoid fungi (Wingfield et al 1993; Seifert et al 2013). This is due to similarities shared across their biology, in key morphological characters, that is believed to have been driven by convergent evolution in adaptation to insect-mediated dispersal (De Beer et al 2013; Wingfield et al 2017b). Ophiostomatoid genera that are most commonly associated with beetles include: Ambrosiella, Endoconidiophora and Graphium in Microascales; and Affroraffaelea, Aureovirgo, Ceratocystiopsis, Fragosphaeria, Graphilbum, Leptographium, Ophiostoma, Raffaelea, and Sporothrix of Ophiostomatales (Hyde et al 2020)
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