Multispecies Phytophthora disease patterns in declining beech stands

Abstract

Decline diseases are typically caused by complex abiotic and biotic interactions and characterized by a suite of symptoms indicative of low plant vigour. Diseased trees are frequently infected by Phytophthora, but the complex interactions between pathogen, host and the heterogeneous forest environment mask a comprehensive understanding of the aetiology. In the present study, we surveyed European beech (Fagus sylvatica) stands in Swiss forests with recent increases in bleeding lesions for the presence of Phytophthora. We used a combined approach of analysing soil and bark samples from trees displaying bleeding lesions and trees free from bleeding lesions. Soil baiting revealed a higher prevalence of Phytophthora spp. around trees with bleeding lesions than around trees without bleeding lesions. For the bark samples from bleeding lesions, we used several detection methods. Phytophthora spp. were detected in 74% of the trees by an immunological on‐site diagnostic kit, in 64% by a specific PCR assay, and 38% by isolation on selective media. All samples tested were negative for P. ramorum using qPCR. Overall, nine Phytophthora species were identified by ITS sequencing, the most common of which were P. plurivora, P. gonapodyides, P. × cambivora and P. syringae. We identified distinct species in bleeding lesions and the rhizosphere of the same host tree which suggests a multispecies Phytophthora disease patterns in these declining beech. Among the recovered species, P. × cambivora and P. × serendipita were identified as hybrid genotypes with the former abundant in bleeding lesions.

Oomycete communities in lowland tropical forest soils vary in abundance and are composed of saprophytes and pathogens of seeds and seedlings of multiple plant species.

“…Similar to the Ohio study, only 42% of the 137 soil samples tested from near Quercus, Betula, Acer and Fagus species in Pennsylvania, USA yielded oomycete isolates (Bily et al 2022). Even when soils were sampled near trees with visible Phytophthora infections in a declining beech forest in Switzerland, only 70% of soils yielded infected bait leaves (Ruffner et al 2019). This suggests that oomycetes are more abundant and active in tropical versus temperate forests.…”

Multivariate Bayesian analysis to predict invasiveness ofPhytophthorapathogens

“…Examples include the pathogen P. ramorum causing sudden oak death in coast live oak ( Quercus agrifolia ) and tanoak ( Notholithocarpus densiflorus ) in western United States (Meentemeyer et al, 2011; Rizzo & Garbelotto, 2003); Phytophthora spp. causing dieback of Proteaceae in Australia and South Africa (Cahill et al, 2008; Nagel et al, 2013); P. agathidicida causing dieback of ancient kauri trees ( Agathis australis ) of great cultural value in northern New Zealand (Bradshaw et al, 2020); and many more (e.g., Fernández‐Habas et al, 2019; Ruffner et al, 2019). These pathogens are irreversibly changing the ecosystems they impact.…”