Phytophthora species in tanoak trees, canopy-drip, soil, and streams in the sudden oak death epidemic area of south-western Oregon, USA

Abstract

Various Phytophthora species were recovered from tanoak trees, tanoak canopy drip, soils, and streams, which were sampled as part of a larger survey and management effort aimed at limiting the spread of Phytophthora ramorum Werres, De Cock & Man in't Veld (the causal agent of sudden oak death) in an epidemic area encompassing native forest and urbanised forest areas in south-western Oregon. Environmental samples were analysed by baiting with either green pear fruits or rhododendron and tanoak leaves. Tanoak bark samples and baits from environmental samples were plated on media semi-selective for the isolation of Phytophthora spp. After incidence of P. ramorum growing on isolation plates was recorded, other Phytophthora species growing on the isolation plates were sub-cultured for identification. DNA sequencing was used to identify the unknown Phytophthora species. A total of seventeen Phytophthora species and one HaloPhytophthora species were identified across all substrates. Over an 8-year period, P. ramorum was detected in cultures from 41% of samples from over 1600 diseased tanoak trees, while other Phytophthora species were detected in 14% of these samples. Of 5189 tanoak canopy drip samples collected over a 4-year period, Phytophthora species other than P. ramorum were detected in 106 samples (2.0%). Of 5967 soil samples baited over an 8-year period, Phytophthora species other than P. ramorum were detected in 71 samples (1.2%). Phytophthora ramorum was detected in ca. 10% of 642 stream samples over a 3-year period, and other Phytophthora species were detected in ca. 86% of these stream samples.

Citation

Reeser, Paul; Wendy Sutton; Everett Hansen. 2011. Phytophthora species in tanoak trees, canopy-drip, soil, and streams in the sudden oak death epidemic area of south-western Oregon, USA. New Zealand Journal of Forestry Science 41S:S65-S73.