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Phenolic chemistry of coast live oak response to Phytophthora ramorum infection

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Ockels, FS and Eyles, A and McPherson, BA and Wood, DL and Bonello, P (2007) Phenolic chemistry of coast live oak response to Phytophthora ramorum infection. Journal of Chemical Ecology, 33 (9). pp. 1721-1732. ISSN 0098-0331

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Abstract

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
Keywords: Sudden oak death . Resistance . Quercus agrifolia . Canker . In vitro bioassay
Journal or Publication Title: Journal of Chemical Ecology
Page Range: pp. 1721-1732
ISSN: 0098-0331
Identification Number - DOI: 10.1007/s10886-007-9332-z
Additional Information:

The original publication is available at www.springerlink.com

Date Deposited: 11 May 2008 22:44
Last Modified: 18 Nov 2014 03:39
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