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Phytophthora ramorum in Canada: Evidence for Migration Within North America and from Europe

January 2011 , Volume 101 , Number  1
Pages  166 - 171

Erica M. Goss, Meg Larsen, Annelies Vercauteren, Sabine Werres, Kurt Heungens, and Niklaus J. Grünwald

First, second, and sixth authors: Horticultural Crops Research Laboratory, United States Department of Agriculture–Agricultural Research Service, Corvallis, OR; third and fifth authors: Institute for Agricultural and Fisheries Research (ILVO), Plant Sciences Unit–Crop Protection, Merelbeke, Belgium; and fourth author: Julius Kuehn Institute—Federal Research Centre for Cultivated Plants, Institute for Plant Protection in Horticulture and Forests, Braunschweig, Germany.

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Accepted for publication 16 September 2010.

Phytophthora ramorum, the cause of sudden oak death on oak and ramorum blight on woody ornamentals, has been reported in ornamental nurseries on the West Coast of North America from British Columbia to California. Long-distance migration of P. ramorum has occurred via the nursery trade, and shipments of host plants are known to have crossed the U.S.–Canadian border. We investigated the genotypic diversity of P. ramorum in Canadian nurseries and compared the Canadian population with U.S. and European nursery isolates for evidence of migration among populations. All three of the P. ramorum clonal lineages were found in Canada but, unexpectedly, the most common was the NA2 lineage. The NA1 clonal lineage, which has been the most common lineage in U.S. nurseries, was found relatively infrequently in Canada, and these isolates may have been the result of migration from the United States to Canada. The EU1 lineage was observed almost every year and shared multilocus genotypes with isolates from Europe and the United States. Estimation of migration rates between Europe and North America indicated that migration was higher from Europe to North America than vice versa, and that unidirectional migration from Europe to North America was more likely than bidirectional migration.

This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 2011.