First Report of Phytophthora europaea in Oak Forests in the Eastern and North-Central United States

Abstract

In 2003 and 2004, soils in oak forest ecosystems in nine central and eastern states of the United States were surveyed for Phytophthora spp. Soil samples were collected around healthy and symptomatic trees. Symptoms included dieback of branches, gaps in lateral branch systems, yellowing of foliage, wilting and clustering of leaves, and the presence of epicormic shoots. Soil subsamples were collected in each of the four cardinal directions and at a distance of 1 to 2 m from the base of a tree. The four subsamples were bulked to produce a sample of approximately 2,000 ml. In the laboratory, each sample was mixed thoroughly and a single 250-g subsample was flooded with 500 ml of distilled water and baited with Quercus robur leaflets for 3 to 5 days at 17 to 20°C. Discolored leaflets were examined microscopically (×200) and those with sporangia typical of Phytophthora spp. were plated on PARPNH selective medium (1). Phytophthora europaea was recovered from soil samples collected from Q. alba in West Virginia, Q. rubra in Minnesota, West Virginia, and Wisconsin, Q. phellos in Ohio, and Q. velutina in Pennsylvania. Cultures were identified as P. europaea by their morphological, physiological, and molecular characteristics (4). Average dimensions of nine isolates were determined. Oogonia were 40 ± 3.9 μm in diameter and often had few bullet protuberances and tapered bases; oospores mostly filled the oogonia and averaged 36 ± 3.7 μm; sporangia dimensions averaged 42 ± 6.1 × 30 ± 4.1 μm with a length/width ratio of 1:4. Isolates produced larger oogonia and oospores but had similar sporangia length/width ratios comparable to the species description (4). Growth optimum (5.8 to 6.9 mm day-1) on V8 juice agar (V8A) occurred at 25°C. On potato dextrose agar, colonies produced dense, felt-like mycelia, often with a central mound of aerial hyphae. DNA also was extracted from eight representative isolates and the internal transcribed spacer (ITS) region of rDNA from each isolate was amplified and sequenced. ITS sequences were identical to those of P. europaea in the NCBI GenBank database (Accession No. DQ313222). Pathogenicity of six isolates (one from each site) was confirmed by wounding stems of 2-year-old Q. alba, Q. rubra, and Q. velutina seedlings and inoculating wounds with V8A plugs (6 mm) containing mycelia; V8A plugs without mycelia were used for controls. Two months after inoculation, P. europaea was reisolated on PARPNH medium from advancing lesions on all inoculated seedlings but was not isolated from control plants. Mean lesion lengths on seedlings inoculated with P. europaea were significantly greater (P < 0.05) than those on control plants; lesions averaged 0.46 cm on Q. alba, 1.38 cm on Q. rubra, and 1.01 cm on Q. velutina. Previously, P. europaea only was reported from oak trees and soil in forests of Austria, France, and Germany (1–4). These findings extend the current distribution of P. europaea and raise questions about its origin and role in the health of oak forests in eastern and north-central United States. Q. alba, Q. phellos, Q. rubra, and Q. velutina are new host associations for P. europaea. References: (1) Y. Balci and E. Halmschlager. For. Pathol. 33:157, 2003. (2) E. Hansen and C. Delatour. Ann. Sci. For. 56:539, 1999. (3) G. Hartmann and R. Blank. Forst Holz. 57:539, 2002. (4) T. Jung et al. Mycol. Res. 106:397, 2002.

Survey of the Phytophthora species diversity revealsP. abietivoraas a potential Phytophthora root rot pathogen in Québec Christmas tree plantations

“…and Q. robur) in France and Germany (Jung et al 2002). It was since then isolated in Europe and associated with Quercus species (Balci and Halmschlager 2003; Tkaczyk et al 2017), in North America associated with diverse deciduous tree species and riparian ecosystems (Balci et al 2006; Reed et al 2019; Reeser et al 2011; Sims et al 2015), and in Australia associated with Dacrydium cupressinum and Iris sibirica (International Collection Of Microorganisms (ICMP) 2022). More recently, surveys of Christmas tree plantations in the US recovered anecdotal P. europaea isolates on Abies fraseri (McKeever and Chastagner 2016; Pettersson et al 2017).…”

“…and Q. robur) in France and Germany (Jung et al 2002). It was since then isolated in Europe and associated with Quercus species (Balci and Halmschlager 2003;Tkaczyk et al 2017), in North America associated with diverse deciduous tree species and riparian ecosystems (Balci et al 2006;Reed et al 2019; Survey (Elmhirst 2017). This study constitutes the first official and well documented report of its presence in Canada's Christmas tree plantations and its association with PRR symptomatic Abies balsamea and A. fraseri.…”

“…and Q. robur) in France and Germany (Jung et al 2002). It was since then isolated in Europe and associated with Quercus species (Balci and Halmschlager 2003;Tkaczyk et al 2017), in North America associated with diverse deciduous tree species and riparian ecosystems (Balci et al 2006;Reed et al 2019;…”

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

“…The question as to whether it is most likely to be P. europaea or P. uliginosa present at the site is an interesting one as both species have been found in rhizosphere soils of Quercus spp. in Europe (Jung et al, 2002), with P. europaea subsequently also isolated from Quercus forests in the USA (Balci et al, 2006). Although P. europaea was found to be only weakly pathogenic on Quercus spp., P. uliginosa is reported to be much more aggressive on these hosts (Jung et al, 2002).…”

Phytophthora species cause sudden and severe decline of naturally regenerated European beech (Fagus sylvatica) seedlings

“…Finally, the impact of P. europaea varied by strain, with one isolate exhibiting a level of virulence comparable to the most aggressive species tested, and the other exhibiting a level of virulence comparable to the less aggressive species. We had no prior information about the potential pathogenicity of P. europaea on F. sylvatica , although it was not considered to be highly pathogenic to oak trees in Europe (Jung et al, 2002) or the United States (Balci et al, 2006). Our results suggest that other factors may impact the aggressiveness of P. europaea .…”