Project Grant 20266704146745

The Department of Agriculture National Institute of Food and Agriculture awarded Oregon State University $500,000 on September 1, 2026, under the Agriculture and Food Research Initiative (CFDA 10.310) to research hybridization of Phytophthora ramorum, the pathogen causing sudden oak death, and to assess threat escalation from hybrid strains in U.S. forests and nurseries.

The project addresses a significant shift in the pathogen's epidemiology. Historically, U.S. populations of P. ramorum belonged to a few genetically uniform clonal lineages with limited capacity to adapt. Oregon State University's research has confirmed that different lineages are now interbreeding to form new hybrid strains across multiple states and counties, with preliminary evidence indicating independent hybridization events and infection of new host plants. Hybrids pose elevated risk because genetic recombination can generate new traits—greater aggressiveness, expanded host range, fungicide resistance, or extended environmental survival—that could undermine quarantine and management strategies developed for the older clonal lineages.

The project will determine the geographic distribution and formation frequency of hybrids, assess their genetic diversity, and compare their aggressiveness and fungicide sensitivity against parent lineages. Oregon State University will conduct forest and nursery surveys in the Pacific Northwest using baited-bucket sampling and CRISPR-based diagnostic assays, test hybrid formation on common nursery plants, sequence hybrid genomes to reconstruct evolutionary origins and potential, and benchmark hybrid pathogenicity and control sensitivity. Results will provide regulators, forest managers, and the nursery industry with early-warning information and diagnostic tools to respond to the emerging threat.

Performance occurs in Corvallis, Oregon. The period of performance runs from September 1, 2026, through August 31, 2028.