Rhododendron leaf baiting of coastal California watersheds for Phytophthora and Nothophytophthora

Abstract

For nearly two decades, stream baiting of northern and central California coastal streams has been an important tool in the management of sudden oak death, a devastating forest disease caused by the oomycete Phytophthora ramorum. Phytophthoraspecies are baited with floating rhododendron leaves, serving as an early detection tool for the presence of P. ramorumin watersheds across more than 800 km of California coastline. While this long-standing management tool is focused on a single species of Phytophthora, other species of Phytophthorahave been baited alongside P. ramorum, and this study documents the presence and distribution of 22 Phytophthoraand Nothophytophthoraspecies across the northern and central coasts of California. Although P. ramorumwas isolated at the greatest number of sites, several species in subgeneric clade 6 were also abundant and widespread, a common feature of Phytophthorastream baiting studies. Clade 3 species P. nemorosa, P. pluvialis, and P. pseudosyringaewere also frequently isolated in northern coastal streams. The species Nothophytophthora caducaand the genus Nothophytophthoraare reported for the first time in North America along with the first report of P. pluvialisin California. Two novel species, Nothophytophthorasp. californicaand P. sp. aureomontensis(a member of the P. citricolaspecies complex) are provisionally named. Mitochondrial sequences revealed multiple hybridization events between P. lacustrisand P. riparia. Stream monitoring can serve as an important tool for monitoring ongoing Phytophthora invasions as well as establishing baseline pathogen communities, critical data for preventing future invasions.

Citation

Bourret, Tyler B.; Mehl, Heather K.; Aram, Kamyar; Rizzo, David M. 2023. Rhododendron leaf baiting of coastal California watersheds for Phytophthora and Nothophytophthora. Mycological Progress. 22(8): 858. https://doi.org/10.1007/s11557-023-01910-8.