Phenolic Chemistry of Coast Live Oak Response to <Emphasis Type="Italic">Phytophthora ramorum</Emphasis> Infection |
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Authors: | Frances S Ockels Alieta Eyles Brice A McPherson David L Wood Pierluigi Bonello |
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Affiliation: | (1) Department of Plant Pathology, The Ohio State University, 201 Kottman Hall, 2021 Coffey Road, Columbus, OH 43210, USA;(2) Present address: Cooperative Research Centre for Forestry/TIAR, University of Tasmania, Private Bag 12, Hobart, 7001, Australia;(3) Center for Forestry and Integrated Hardwood Rangeland Management Program, Department of Environmental Science, Policy, and Management, University of California, 145 Mulford Hall, Berkeley, CA 94720, USA;(4) Division of Organisms and Environment, Department of Environmental Science, Policy and Management, University of California, 201 Wellman Hall, Berkeley, CA 94720, USA |
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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.
Frances S. Ockels and Alieta Eyles contributed equally to the paper |
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Keywords: | Sudden oak death Resistance Quercus agrifolia Canker In vitro bioassay |
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