Growth, infection and aggressiveness of Phytophthora pathogens on Rhododendron leaves

Clare R Taylor,Niklaus J Grünwald

doi:10.1186/s43170-021-00048-5

Clare R Taylor, Niklaus J Grünwald

Open Access

https://doi.org/10.1186/s43170-021-00048-5

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Abstract

BackgroundPhytophthora species are well known as important or emerging pathogens. The genus Rhododendron is of considerable importance to plant regulatory agencies because it is host to many Phytophthora species, most notably, P. ramorum and P. kernoviae. Few studies have directly contrasted the epidemiology of different Phytophthora spp. on a given host.MethodsWe investigated aspects of the foliar epidemiology (lesion size, sporulation and temperature responses) of P. cactorum, P. cambivora, P. cinnamomi, P. citrophthora, P. foliorum, P. kernoviae, P. lateralis, P. nemorosa, P. nicotianae, P. plurivora, P. ramorum and P. syringae on Rhododendron in detached leaf, whole plant chamber, and field studies.ResultsP. syringae stood out as it appeared to be a relatively weak pathogen, showing no sporulation and low levels of disease severity, except at low temperatures. P. nicotianae was consistently able to grow at higher temperatures than any of the other Phytophthora spp. and showed higher aggressiveness than any of the other species at high temperatures. P. cinnamomi and P. cactorum, typically thought of as root-infecting species, were able to cause as much foliar disease as P. syringae, a foliar pathogen. P. kernoviae was consistently among the most aggressive species with the highest sporulation.ConclusionThese results provide novel insights into the comparative epidemiology of these important established and emerging Phytophthora species.

Highlights

Phytophthora species are well known as important or emerging pathogens
The genus Rhododendron is of considerable importance to plant regulatory agencies because it is host to many Phytophthora species, most notably, P. ramorum and P. kernoviae (Brasier et al 2005; Werres et al 2001; Grünwald et al 2008)
Species and isolates The Phytophthora species used in this study were P. cactorum, P. cambivora, P. cinnamomi, P. citrophthora, P. foliorum, P. kernoviae, P. lateralis, P. nemorosa, P. nicotianae, P. plurivora, P. ramorum and P. syringae (Table 1)

Summary

Introduction

Phytophthora species are well known as important or emerging pathogens. Notable examples include the jarrah dieback pathogen P. cinnamomi (Hardham 2005), the sudden oak death pathogen P. ramorum (Grünwald et al 2008), and the potato late blight pathogen P. infestans (Fry 2008). Taylor and Grünwald CABI Agric Biosci (2021) 2:26 occur on asymptomatic plants or with pathogen propagules in potting media. This is thought to have been the case with the import of ornamental plants such as Rhododendron, Pieris, Viburnum, and Camellia into the USA, and hypothesized to be involved in the introduction of P. ramorum into California (Mascheretti et al 2008), the Pacific Northwest (Goss et al 2009, 2011), and Europe (Van Poucke et al 2012). Phytophthora species are well known as important or emerging pathogens. The genus Rhododendron is of considerable importance to plant regulatory agencies because it is host to many Phytophthora species, most notably, P. ramorum and P. kernoviae. Few studies have directly contrasted the epidemiology of different Phytophthora spp. on a given host

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