Phytophthora is a group of destructive microscopic plant pathogens found in the Kingdom Protista. This water mold poses a substantial threat in the Pacific Northwest, as it infects rhododendron leaves. More Phytophthora are yet to be found here than are currently documented. Understanding the factors that contribute to the diversity of Phytophthora species found in an area is essential in predicting where the spread of this species is most likely. It is hypothesized greater levels of rainfall increase Phytophthora diversity. The sampling location, Chambers Creek in Pierce County, WA, is situated in an area of comparatively moderate rainfall; therefore, about three species are expected to be found. After baiting Chambers Creek with rhododendron leaves, PARP agar was inoculated, then Phytophthora was isolated. DNA was analyzed and bioinformatics was used to identify species present. By understanding the number of Phytophthora species present in local creeks, patterns in WA can be identified to help control this plant pathogen. Our samples identified three species of Phytophthora present in Chambers Creek. This matches our hypothesis that moderate levels of rainfall correspond to moderate species diversity. Based on the specific species found, we suggest to continue monitoring, but no urgent action is needed.

Phytophthora is a genus of oomycete water molds that harms plants. They are a group of fungi-like microbes responsible for several plant diseases, including blight, canker, dieback, and root rot. Even though approximately 30 species have been identified in Oregon and Alaska, the number of species currently present in Washington is yet to be determined. Our research focuses on the diversity of Phytophthora species. First, in an analysis of previously collected data and US Census data, the Phytophthora species diversity is higher in counties with a higher human population. Based on this analysis, we expected to find more than three species of Phytophthora present in Chambers Creek (our sample site) due to the high human population in Pierce County. Secondly, we sampled Chambers Creek for nine days using Rhododendron leaves, incubated the leaves for two days, then performed a PCR. The PCR product was sequenced using Sanger sequencing and a BLAST was used to identify the species present in our sample. Ultimately, we identified four species of the harmful plant pathogen Phytophthora present in Chambers Creek. From this, we conclude that there is a high diversity of Phytophthora present in this Pierce County water source. Phytophthora can be extremely harmful to trees and crops, and it has caused mass famines in the past. This research is vital because understanding patterns of its diversity allows us to monitor its presence locally; should a particularly harmful species be found, we can work to mitigate its effect on our ecosystems.