Metabarcoding reveals a high diversity of woody host-associatedPhytophthoraspp. in soils at public gardens and amenity woodlands in Britain

Abstract

Forests and woodlands worldwide are being severely impacted by invasivePhytophthoraspecies, with initial outbreaks in some cases occurring on host trees located in public parks and gardens. These highly disturbed sites with diverse planting practices may indeed act as harbours for invasivePhytophthorapathogens which are particularly well adapted to surviving in soil. High throughput Illumina sequencing was used to analysePhytophthoraspecies diversity in soil samples collected from 14 public garden/amenity woodland sites in northern Britain. Bioinformatic analyses revealed some limitations to using internal transcribed spacer as the barcode region; namely reporting of false positives and ambiguous species matches. Taking this into account, 35 distinct sequences were amplified across the sites, corresponding to 23 knownPhytophthoraspecies as well as twelve oomycete sequences with no match to any knownPhytophthoraspecies.Phytophthora pseudosyringaeandP. austrocedri, both of which cause serious damage to trees and are regarded as fairly recent introductions to Britain, were the two most abundantPhytophthoraspecies detected. There was no evidence that any of the detectedPhytophthoraspecies were more associated with any one type of host, healthy or otherwise. This study has demonstrated the ubiquity and diversity ofPhytophthoraspecies endemic in highly managed, extensively planted soil environments in Britain. Suggested improvements to the methodology and the practical implications of the findings in terms of mitigatingPhytophthoraspread and impact are discussed.