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United States Department of Agriculture

Agricultural Research Service

Title: Phylogenetic Relationships of Phytophthora Ramorum and a Phytophthora Ilicis-Like Species Associated with Sudden Oak Death in California

Authors
item Martin, Frank
item Tooley, Paul

Submitted to: Mycological Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 13, 2003
Publication Date: December 20, 2003
Citation: Martin, F.N., Tooley, P.W. 2003. Phylogenetic relationships of phytophthora ramorum and a phytophthora ilicis-like species associated with sudden oak death in california. Mycological Research. v. 107. p. 1379-1391.

Interpretive Summary: Sudden Oak Death has been an emerging disease problem in coastal California and has caused significant losses in forest ecosystems in some regions of the state. Phytophthora ramorum, the causal agent of this disease, and a P. ilicis-like species that is recovered from some symptomatic plants were examined to determine their phylogenetic relationship with other species in the genus by sequence alignment of the mitochondrially-encoded cytochrome oxidase II gene and the nuclear encoded rDNA internal transcribed spacer region. P. ramorum was most closely related to P. hibernalis and P. lateralis while the P. ilicis-like species was most closely related to P. ilicis. Both P. ramorum and the P. ilicis-like species represented distinct species and were not likely the result of interspecific crosses between species. The results will help other scientists better understand the relationships among these pathogens and other members of the genus. Also, the DNA sequence information obtained may be used to develop identification and detection methods for these pathogens.

Technical Abstract: Sudden Oak Death has been an emerging disease problem in coastal California and has caused significant losses in forest ecosystems in some regions of the state. P. ramorum, the causal agent of this disease, and a P. ilicis-like species were examined to determine their phylogenetic relationship with other species in the genus by sequence alignment of 667 bp of the mitochondrially-encoded cox II gene and the nuclear encoded rDNA internal transcribed spacer region. P. ramorum was most closely related to P. hibernalis and P. lateralis in both trees, although the specific relationship among species differed depending on the tree. In the cox II tree these species were on a single clade with P. lateralis basal to a P. ramorum and P. hibernalis grouping. On the ITS tree based on maximum parsimony P. ramorum was most closely affiliated with P. lateralis and on the same clade as P. hibernalis. However, with maximum likelihood analysis P. ramorum was most closely affiliated with P. hibernalis and on the same clade as P. lateralis. In all analyses the bootstrap support for these groupings was not strong. In contrast to the cox II tree, the clade containing these species grouped with P. cryptogea, P. drechsleri, P. erythroseptica, and P. syringae in the ITS tree. Since the same isolates of these species were used for both the cox II and ITS sequence analysis, this difference in species grouping suggests either a differential rate of evolutionary divergence for these two regions or incorrect assumptions about alignment of ITS sequences. Both trees supported a close relationship between P. ilicis and the P. ilicis-like isolates. Data would suggest that P. ramorum and the P. ilicis-like isolates are phylogenetically distinct new species and not the result of interspecific hybridization.

Last Modified: 10/25/2014
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