Diversity of woody-host infecting Phytophthora species in public parks and botanic gardens as revealed by metabarcoding, and opportunities for mitigation through best practice

Abstract

The diversity of Phytophthora species in soils collected from 14 highly disturbed sites in northern Britain, including botanic gardens, arboreta, public parks and other amenity woodland sites, was analysed using a molecular technique known as DNA metabarcoding. This technique enables the identification of multiple species present in a single environmental sample based on a DNA ‘barcode’ unique to each species. The genus Phytophthora was targeted in this study due to its increasing impact on Britain’s forests and woodlands over thelast 20 years. The introduction and spread of new Phytophthora species into Britain has been strongly associated with the movement of traded containerised plants, with a number of Phytophthora outbreaks reported on host trees located in public gardens and parks that had recently undergone planting or landscape regeneration schemes. This study was undertaken to assess the extent to which these highly disturbed sites with extensive planting regimes act as harbours for woody-host infecting Phytophthora species. A total of 23 Phytophthora species, the majority of which are known to be pathogens of woody hosts, were detected across the 14 sites sampled. These included four quarantine-regulated pathogens and four species notpreviously recorded in Britain. Also detected were three as-yet undescribed Phytophthora species and nine oomycete sequences with no clear match to any known genus. There was no effect of geographical location, elevation, underlying soil type, host family or host health status on the Phytophthora assemblages at each site, suggesting that the Phytophthora communities detected are likely to comprise introduced species associated with planting programmes. P. austrocedri and P. pseudosyringae were two of the most abundant Phytophthoraspecies detected, both of which cause serious damage to trees and are regarded as fairly recent introductions to Britain. The practical implications of the findings in terms of mitigating Phytophthora introduction, spread and impact at botanic gardens, arboreta and urban parks are discussed.

Comparison of Primers for the Detection of Phytophthora (and Other Oomycetes) from Environmental Samples

“…Internal controls were not included in the current study but would be a valuable addition to any protocol. Green et al [38] included four samples containing a mix of synthetic 'Phytophthora' sequences of known base composition on the plate as a check for sequence contamination. These can be synthetic reference sequences included in the initial PCR reactions as control samples to determine any cross-contamination during the amplification stage.…”

Monitoring oomycetes in water: combinations of methodologies used to answer key monitoring questions

“…The baits selected for an assay strongly influence the resulting catch: for example, autoclaved insect parts are likely to attract Saprolegniales and some Pythium species (Sarowar et al, 2013), whereas fresh, whole rhododendron leaves work well for Phytophthora species in temperate streams and hardy nursery-stock irrigation systems (Themann and Werres, 1998;Themann et al, 2002). Green et al (2020) effectively deployed a mix of different fresh leaf species as baits in a study investigating the range of Phytophthora species present in public parks, whilst in comparative trials in Australia, primarily looking at soils, a multiple bait system used by the Centre for Phytophthora Science and Management was the most effective baiting procedure (Burgess et al, 2021). The age, quality, and physiological state of the plant tissues being used as baits are hugely influential on the results obtained (Themann et al, 2002;Hüberli et al, 2013;Werres et al, 2014), and inclusion of dead tissues within a bait mix can increase the number of species captured (Wielgoss et al, 2009;Aram and Rizzo, 2018;Sarker et al, 2023a).…”

“…procedures which offer high levels of accuracy, sensitivity and some measure of abundance or relative abundance of detected taxa (Green et al, 2020;Green et al, 2021).…”

Phylogeography, origin and population structure of the self‐fertile emerging plant pathogen Phytophthora pseudosyringae

“…It is likely that the variable caducity of P. pseudosyringae sporangia has helped the species thrive in a range of habitats and ecosystems, cause a variety of symptoms including root necrosis, collar rot and stem, twig and foliar lesions and infect an ever‐expanding range of hosts (Beales et al., 2010 ; Bregant et al., 2023 ; Denman et al., 2009 ; Green et al., 2020 ; Jung et al., 2016 ; Reeser et al., 2011 ; Scanu & Webber, 2016 ; Wickland et al., 2008 ; Yakabe et al., 2009 ). It has caused severe dieback of Nothofagus spp.…”