Distribution and diversity of Phytophthora across Australia

The introduction and subsequent impact of Phytophthora cinnamomi within native vegetation is one of the major conservation issues for biodiversity in Australia. Recently, many new Phytophthora species have been described from Australia’s native ecosystems; however, their distribution, origin, and potential impact remain unknown. Historical bias in Phytophthora detection has been towards sites showing symptoms of disease, and traditional isolation methods show variable effectiveness of detecting different Phytophthora species. However, we now have at our disposal new techniques based on the sampling of environmental DNA and metabarcoding through the use of high-throughput sequencing. Here, we report on the diversity and distribution of Phytophthora in Australia using metabarcoding of 640 soil samples and we compare the diversity detected using this technique with that available in curated databases. Phytophthora was detected in 65% of sites, and phylogenetic analysis revealed 68 distinct Phytophthora phylotypes. Of these, 21 were identified as potentially unique taxa and 25 were new detections in natural areas and/or new introductions to Australia. There are 66 Phytophthora taxa listed in Australian databases, 43 of which were also detected in this metabarcoding study. This study revealed high Phytophthora richness within native vegetation and the additional records provide a valuable baseline resource for future studies. Many of the Phytophthora species now uncovered in Australia’s native ecosystems are newly described and until more is known we need to be cautious with regard to the spread and conservation management of these new species in Australia’s unique ecosystems.