02442nas a2200145   4500008004100000022001400041245011800055210006900173260001600242520189900258100002902157700002702186700001702213856006602230       2020                        eng d  a0191-291700aSporulation potential of Phytophthora ramorum differs among common California plant species in the Big Sur region0 aSporulation potential of Phytophthora ramorum differs among comm  cNov-17-20203 a<p>Sudden oak death (SOD), caused by the generalist pathogen <em>Phytophthora ramorum</em>, has profoundly impacted California coastal ecosystems. SOD has largely been treated as a two-host system, with <em>Umbellularia californica</em> as the most transmissive host, <em>Notholithocarpus densiflorus</em> less so, and remaining species as epidemiologically unimportant. However, this understanding of transmission potential primarily stems from observational field studies rather than direct measurements on the diverse assemblage of plant species. Here, we formally quantify the sporulation potential of common plant species inhabiting SOD-endemic ecosystems on the California coast in the Big Sur region. This study allows us to better understand the pathogen’s basic biology, trajectory of SOD in a changing environment, and how the entire host community contributes to disease risk. Leaves were inoculated in a controlled laboratory environment and assessed for production of sporangia and chlamydospores, the infectious and resistant propagules, respectively. <em>P. ramorum</em> was capable of infecting every species in our study and almost all species produced spores to some extent. Sporangia production was greatest in <em>N. densiflorus</em> and <em>U. californica</em> and the difference was insignificant. Even though other species produced much less, quantities were non-zero. Thus, additional species may play a previously unrecognized role in local transmission. Chlamydospore production was highest in <em>Acer macrophyllum</em> and <em>Ceanothus oliganthus</em>, raising questions about the role they play in pathogen persistence. Lesion size did not consistently correlate with the production of either sporangia or chlamydospores. Overall, we achieved an empirical foundation to better understand how community composition affects transmission of <em>P. ramorum</em>.</p>1 aRosenthal, Lisa, Micaela1 aFajardo, Sebastian, N.1 aRizzo, David  uhttps://apsjournals.apsnet.org/doi/10.1094/PDIS-03-20-0485-RE