Characterizing newly emerging hybrids of the sudden OAK death pathogen -- objective 1: survey forest and nursery isolates of phytophthora ramorum for the presence of hybrids and validate hybrid…

The Department of Agriculture Agricultural Research Service awarded Oregon State University a $529,480 cooperative agreement on September 1, 2026, for research on newly emerging hybrid strains of Phytophthora ramorum, the pathogen causing sudden oak death, under the Agricultural Research Basic and Applied Research program (CFDA 10.001).

The award funds four coordinated research objectives. The first objective surveys forest and nursery isolates of P. ramorum for hybrid presence and validates diagnostic assays to determine the extent and frequency of hybridization events. The Oregon Department of Forestry and U.S. Forest Service provide weekly samples from SOD outbreak sites, and the California Department of Food and Agriculture and Oregon Department of Agriculture supply nursery plant samples for diagnostics. The second objective compares aggressiveness, host range, and sporulation among lineages and hybrids on common plant species in nurseries and forests to inform revised mitigation strategies. The third objective remeasures 88 permanent plots established in 2020 and 2021 across treated sites, control stands, and untreated infestations in southwest Oregon forests to evaluate the impact of disease development and treatment on forest dynamics over a five-year interval. The fourth objective evaluates how host stress and metalaxyl fungicide application affect P. ramorum genome stability, examining changes in fitness and fungicide resistance at the genomic level.

Performance occurs in Corvallis, Oregon, with a period of performance from September 1, 2026, through August 31, 2030.

Characterizing newly emerging hybrids of the sudden OAK death pathogen -- objective 1: survey forest and nursery isolates of phytophthora ramorum for the presence of hybrids and validate hybrid diagnostic assay. Surveying is critical for determining the extent and frequency of hybridization events. Additionally, assembling a comprehensive collection of hybrids is essential for reconstructing their evolutionary histories, assessing their trajectories, and developing new evidence-based management strategies. The oregon department of forestry and the US forest service currently survey the (sudden OAK death) SOD outbreak and provide samples to the cooperator on a weekly basis for diagnostics. The cfda and ODA also survey nursery plants for p. Ramorum and regularly provide samples to the USDA-ARS. Up to now, the identification of hybrids has not been routinely conducted, as their existence was not known. Objective 2: compare the relative aggressiveness among lineages and hybrids on common plant species in nurseries and forests. The high evolutionary potential of hybrids may alter fitness, and understanding these changes is essential for developing or revising mitigation strategies. Important traits are aggressiveness, host range, and sporulation. Objective 3: conduct 5-year RE-measurement of permanent-plot network in southwest oregon. A total of 88 plots were established in 2020 and 2021 in the forests of southwest oregon. These plots encompassed treated sites, control stands, and untreated infestations. We will remeasure these sites to evaluate the impact of disease development and treatment on forest dynamics. Objective 4: evaluate the effect of host stress and fungicide application (metalaxyl) on p. Ramorum genome stability. In other phytophthora SPP. Stress has been demonstrated to affect genome stability, fitness, and fungicide resistance. We will evaluate how p. Ramorum will respond to host and fungicide induced stress at the genome level. Isolates with these changes are less aggressive and sporulate less. Understanding this process could lead to novel management approaches for p. Ramorum. Objective 5: compare disease resistance and genetic diversity of residual surviving tanoak trees to that of the broader population. Not all tanoak trees have been killed by the SOD. We will compare the relative levels of resistance of seedlings grown from these parent trees with seedlings grown from tanoak trees in healthy stands. Objective 6: determine how long p. Ramorum can survive in tanoak logs after harvest. Currently, the regulations for southwest oregon prevent the movement of tanoak logs outside of the quarantine area prior to processing. Determining the length of time p. Ramorum is viable in harvested tanoak trees could have potential implications for the use and movement of logs outside the quarantine area.