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Abstract Recent advances in the field of environmental DNA (eDNA) metabarcoding have produced a promising platform for early detection and broad‐spectrum monitoring of plant pests and pathogens. To date, the majority of fungal metabarcoding assays have relied upon universal primers amplifying segments of the ribosomal DNA, to ensure broad taxonomic coverage while studying changes in community composition, or more recently, to screen for presence/absence of target species. In a diagnostics framework however, single, universal molecular barcodes do not discriminate accurately enough for many groups of important fungal phytopathogens at the required species level. Here, a modular, multi‐barcode amplicon sequencing pipeline was established to provide rapid and reliable diagnostics targeting the Ophiostomatales, an order containing economically important phytopathogens vectored by bark and ambrosia beetles (Curculionidae). Using compositionally varied mock communities, we evaluated five barcoding loci: ITS1, ITS2, the large ribosomal sub‐unit (LSU), translation elongation factor 1‐alpha (TEF1α) and calmodulin (CAL), for their ability to provide species‐level resolution. The sensitivity and detection limit of the assay was established by spiking genomic DNA of the exotic Dutch elm disease pathogen, Ophiostoma novo‐ulmi Brasier, into both the controlled mock communities and eDNA sampled from Ips grandicollis (Eichhoff) beetles collected in New South Wales, Australia. The TEF1α barcode successfully detected the Dutch elm pathogen DNA with 100% accuracy down to approx. 5 pg/μl, while the ITS1 barcode had a 100% accuracy down to approx. 0.4 pg/μl within a given sample. Our results demonstrate that a dual‐barcode approach targeting the ITS1 and TEF1α regions simultaneously is sufficient for accurate species level detection and characterisation of the Ophiostomatales and offers confident detection of low‐abundance taxa (relative read abundances of 0.1%–0.01%). Multi‐barcode metabarcoding provides a framework which can quickly and efficiently be adapted to new targets when establishing high throughput diagnostics for post‐border biosecurity surveillance of fungal phytopathogens.

Background The Australian citrus industry remains one of the few in the world to be unaffected by the African and the Asian citrus psyllids, Trioza erytreae Del Guercio and Diaphorina citri Kuwayama, respectively, and the diseases their vectored bacteria can cause. Surveillance, early detection, and strict quarantine measures are therefore fundamental to safeguard Australian citrus. However, long-term targeted surveillance for exotic citrus pests can be a time-consuming and expensive activity, often relying on manually screening large numbers of trap samples and morphological identification of specimens, which requires a high level of taxonomic knowledge. Methods Here we evaluated the use of non-destructive insect metabarcoding for exotic pest surveillance in citrus orchards. We conducted an 11-week field trial, between the months of December and February, at a horticultural research farm (SuniTAFE Smart Farm) in the Northwest of Victoria, Australia, and processed more than 250 samples collected from three types of invertebrate traps across four sites. Results The whole-community metabarcoding data enabled comparisons between different trapping methods, demonstrated the spatial variation of insect diversity across the same orchard, and highlighted how comprehensive assessment of insect biodiversity requires use of multiple complimentary trapping methods. In addition to revealing the diversity of native psyllid species in citrus orchards, the non-targeted metabarcoding approach identified a diversity of other pest and beneficial insects and arachnids within the trap bycatch, and recorded the presence of the triozid Casuarinicola cf warrigalensis for the first time in Victoria. Ultimately, this work highlights how a non-targeted surveillance approach for insect monitoring coupled with non-destructive DNA metabarcoding can provide accurate and high-throughput species identification for biosecurity and biodiversity monitoring.

Post-border surveillance for forestry’s high priority pests and pathogens is conducted routinely through established programs focused on the main points-of-entry and across the major plantation growing regions. Currently, most diagnostic protocols used to identify fungal phytopathogens sampled during these surveys rely on traditional methods, such as morphological examination and DNA barcoding techniques. This stepwise process from isolation to species identification is often regarded as slow, expensive, and limited due to the need for disease manifestation and/or comprehensive expertise for rapid and accurate detection. In this study, we applied a recently validated high-throughput, dual-marker amplicon sequencing approach on insect surveillance traps from across Australia to assess its performance for the targeted surveillance of the Ophiostomatales, an order of fungi comprising notable phytopathogens which are vectored by bark beetles. By using a recently validated assay we were able to confidently characterize a range of Ophiostomatalean taxa known to be present in Australia, while reporting eight first detections from environmental DNA. Our study demonstrates the value of targeted multi-barcode amplicon sequencing for high-throughput screening of fungi caught in post-border surveillance traps, in addition to emphasizing research priorities that require further investigation before such methods can be implemented routinely for biosecurity.

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.

Abstract Background The taxonomic history of Ceratocystis, a genus in the Ceratocystidaceae, has been beset with questions and debate. This is due to many of the commonly used species recognition concepts (e.g., morphological and biological species concepts) providing different bases for interpretation of taxonomic boundaries. Species delineation in Ceratocystis primarily relied on genealogical concordance phylogenetic species recognition (GCPSR) using multiple standard molecular markers. Results Questions have arisen regarding the utility of these markers e.g., ITS, BT and TEF1-α due to evidence of intragenomic variation in the ITS, as well as genealogical incongruence, especially for isolates residing in a group referred to as the Latin-American clade (LAC) of the species. This study applied a phylogenomics approach to investigate the extent of phylogenetic incongruence in Ceratocystis. Phylogenomic analyses of a total of 1121 shared BUSCO genes revealed widespread incongruence within Ceratocystis, particularly within the LAC, which was typified by three equally represented topologies. Comparative analyses of the individual gene trees revealed evolutionary patterns indicative of hybridization. The maximum likelihood phylogenetic tree generated from the concatenated dataset comprised of 1069 shared BUSCO genes provided improved phylogenetic resolution suggesting the need for multiple gene markers in the phylogeny of Ceratocystis. Conclusion The incongruence observed among single gene phylogenies in this study call into question the utility of single or a few molecular markers for species delineation. Although this study provides evidence of interspecific hybridization, the role of hybridization as the source of discordance will require further research because the results could also be explained by high levels of shared ancestral polymorphism in this recently diverged lineage. This study also highlights the utility of BUSCO genes as a set of multiple orthologous genes for phylogenomic studies.