Phytophthora pachypleura sp. nov., a new species causing root rot of Aucuba japonica and other ornamentals in the United Kingdom

B. Henricot,A. Pérez Sierra,T. Jung

doi:10.1111/ppa.12194

B. Henricot, A. Pérez Sierra + Show 1 more

Open Access

https://doi.org/10.1111/ppa.12194

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Abstract

Isolates of an unknown Phytophthora species from the ‘Phytophthora citricola complex’ have been found associated with mortality of Aucuba japonica in the UK. Based on morphological characteristics, growth–temperature relationships, sequences of five DNA regions and pathogenicity assays, the proposed novel species is described as Phytophthora pachypleura. Being homothallic with paragynous antheridia and semipapillate sporangia, P. pachypleura resembles other species in the ‘P. citricola complex’ but can be discriminated by its distinctively thick‐walled oospores with an oospore wall index of 0·71. In the phylogenetic analysis based on three nuclear (ITS, β‐tubulin, EF‐1α) and two mitochondrial (cox1, nadh1) DNA regions, P. pachypleura formed a distinct clade within the ‘P. citricola complex’ with P. citricola s. str., P. citricola E and P. acerina as its closest relatives. Phytophthora pachypleura is more aggressive to A. japonica than P. plurivora and P. multivora and has the potential to affect other ornamental species.

Highlights

More than 120 Phytophthora species are officially described and another 40–50 Phytophthora taxa have been informally designated (Erwin & Ribeiro, 1996; Blair et al, 2008; Brasier, 2009; Jung et al, 2011; Hansen et al, 2012)
This paper reports a new homothallic species belonging to the ‘P. citricola complex’ of Phytophthora internally transcribed spacer (ITS) Clade 2, which is described here as P. pachypleura
The discovery of this new species came as a result of an investigation initiated in 1999 by the Royal Horticultural Society (RHS) into the threat of Phytophthora species to ornamentals grown in UK gardens

Summary

Introduction

More than 120 Phytophthora species are officially described and another 40–50 Phytophthora taxa have been informally designated (Erwin & Ribeiro, 1996; Blair et al, 2008; Brasier, 2009; Jung et al, 2011; Hansen et al, 2012). Brasier, 2009; Jung et al, 2011, 2013; Hansen et al, 2012) and recent expeditions in remote areas of Asia and South America, many new Phytophthora species have been detected and the origins and possible pathways of wellknown Phytophthora species have been elucidated

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