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POSTERS: Population biology and genetics

Epidemic dynamics of multiple introductions of the sudden oak death pathogen into Oregon forests
Nicholas Carleson - Oregon State University. Jared LeBoldus- Oregon State University, Sarah Navarro- Oregon Department of Forestry, Meredith Larson- USDA ARS, Niklaus Grunwald- Oregon State University, Hazel Daniels- Oregon State University, Niklaus Grunwald- USDA ARS

Sudden oak death (SOD) has been actively managed in Oregon since the early 2000’s. There are currently four recognized clonal lineages, with the NA1 lineage being primarily responsible for the epidemic in southwest Oregon forests. We compared population dynamics of the NA1 Phytophthora ramorum outbreak first reported in 2001 to an outbreak of an emerging EU1 P. ramorum clonal lineage first detected in 2015. We also tested if NA1 was reintroduced since the initial documentation of two introductions. Infested regions of the forest were sampled between 2013-2018 (n=903) and screened at 15 microsatellite loci. Most genotypes were transient, with 272 of 358 unique genotypes emerging one year and disappearing the next. Diversity of EU1 was very low and isolates were geospatially clustered (<8 km apart), suggesting a single EU1 introduction. Some forest isolates are genetically similar to isolates collected from a local nursery in 2012, suggesting introduction of EU1 from this nursery or simultaneous introduction to both the nursery and latently into the forest. In contrast, the older NA1 populations were more polymorphic and spread over 30 km. Principal component analysis supported two to four independent NA1 introductions. The NA1 and EU1 epidemics infest the same area but show disparate demographies owing to initial introductions spaced 10 years apart. Comparing these epidemics provides novel insights into patterns of emergence of clonal pathogens in forest ecosystems.