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Phenolic chemistry of coast live oak response to Phytophthora ramorum infection


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Ockels, FS, Eyles, A, McPherson, BA, Wood, DL and Bonello, P 2007 , 'Phenolic chemistry of coast live oak response to Phytophthora ramorum infection' , Journal of Chemical Ecology, vol. 33 , pp. 1721-1732 , doi: 10.1007/s10886-007-9332-z.

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Since the mid 1990s, Phytophthora ramorum has been responsible for the
widespread mortality of tanoaks, as well as several oak species throughout California and
Oregon forests. However, not all trees die, even in areas with high disease pressure, suggesting
that some trees may be resistant to the pathogen. In this study, the chemical basis of
host resistance was investigated. Three field experiments were carried out in California
between December 2004 and September 2005. The levels of nine phenolic compounds
(gallic acid, catechin, tyrosol, a tyrosol derivative, ellagic acid, and four ellagic acid derivatives)
extracted from the phloem of trees that had been either artificially inoculated with P.
ramorum or trees putatively infected with P. ramorum (based on canker symptoms) were
quantified by high-performance liquid chromatography (HPLC). Significant differences in
phenolic profiles were found between phloem sampled from the active margins of cankers,
healthy phloem from asymptomatic trees, and phloem sampled 60 cm away from canker
sites, although the magnitude and direction of the responses was not consistent across all
experiments. Concentrations of gallic acid, tyrosol, and ellagic acid showed the greatest
differences in these different tissues, but varied considerably across treatments. Gallic acid and tyrosol were tested in in vitro bioassays and showed strong dose-dependent inhibitory
effects against P. ramorum, P. cinnamomi, P. citricola, and P. citrophthora. These results
suggest that phloem chemistry varies in response to pathogen infection in California coast
live oak populations and that changes in phloem chemistry may be related to apparently
resistant phenotypes observed in the field.

Item Type: Article
Authors/Creators:Ockels, FS and Eyles, A and McPherson, BA and Wood, DL and Bonello, P
Keywords: Sudden oak death . Resistance . Quercus agrifolia . Canker . In vitro bioassay
Journal or Publication Title: Journal of Chemical Ecology
Publisher: Springer New York LLC
ISSN: 0098-0331
DOI / ID Number: 10.1007/s10886-007-9332-z
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