Oral Technical Session: Fungal Genetics and Genomics

100-O

Genome-wide patterns of diversity in four lineages of the sudden oak death pathogen, Phytophthora ramorum.
A. L. DALE (1), S. E. Everhart (2), N. Feau (1), G. J. Bilodeau (3), N. J. Grunwald (4), R. C. Hamelin (1)
(1) University of British Columbia, Vancouver, BC, Canada; (2) Oregon State University, Corvallis, OR, U.S.A.; (3) Canadian Food Inspection Agency, Ottawa, ON, Canada; (4) Horticultural Crops Research Laboratory, USDA ARS, Corvallis, OR, U.S.A.

Phytophthora ramorum causes leaf blight on over 100 hosts and a lethal stem canker on Japanese larch, some oak species and European beech. There are four known lineages which have been introduced and are spreading in Europe and North America from an unknown source. The recent host jump to Japanese larch, a commercially important species in Europe, and subsequent wide-scale mortality in plantations has raised concerns on the potential impact on the forest industry and international trade. We conducted a large scale genome re-sequencing effort (92 strains) to gain insight on migration and evolutionary history of P. ramorum. We found a high level of fixed heterozygosity within lineages reinforcing the idea that these lineages evolved from a sexually reproducing ancestor but are now mainly clonal. Despite this, we have found sufficient intra-lineage diversity (pi = 0.00308, 0.00216 and 0.00223 in EU1, EU2 and NA1) for analysis of migration patterns in North America. We also found several lineage-specific genes including genes encoding effector-like proteins and transposons, suggesting some gain/loss patterns of pathogenicity-genes during lineage evolution. Inter-lineage comparisons using genome re-sequencing should provide insight into the ancestor population from which these lineages evolved. Intra-lineage comparisons will be important in determining migration patterns and allow quarantine efforts to be focused on pathways likely to cause future pathogen introductions.