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ARS Home » Northeast Area » Beltsville, Maryland (BARC) » Beltsville Agricultural Research Center » Mycology and Nematology Genetic Diversity and Biology Laboratory » Research » Publications at this Location » Publication #418622
Research Project: Fungal Systematics and Diagnostic Resource Development for Safeguarding Plant Health

Location: Mycology and Nematology Genetic Diversity and Biology Laboratory

Title: Phytophthora species and their associations with Chaparral and oak woodland vegetation in Southern California

Author
item FAJARDO, SEBASTIAN - University Of California
item Bourret, Tyler
item FRANKEL, SUSAN - Us Forest Service (FS)
item RIZZO, DAVID - University Of California

Submitted to: The Journal of Fungi
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/3/2025
Publication Date: 1/4/2025
Citation: Fajardo, S.N., Bourret, T.B., Frankel, S.J., Rizzo, D.M. 2025. Phytophthora species and their associations with Chaparral and oak woodland vegetation in Southern California. The Journal of Fungi. 11(1):33. https://doi.org/10.3390/jof11010033.
DOI: https://doi.org/10.3390/jof11010033

Interpretive Summary: The genus Phytophthora is a group of devastating plant pathogens that threaten plants in agriculture, horticulture and forests. Phytophthora species have been spread worldwide, often associated with the movement of living plants, including those used for purposes of ecological restoration. A survey was conducted across Angeles National Forest (ANF) in California, USA, where restoration practices are common. Fourteen species of Phytophthora were found associated with a variety of woody plants. This research will benefit vegetation ecologists, forest health practitioners and a variety of ANF stakeholders, as well as Phytophthora researchers and regulators worldwide.

Technical Abstract: Evidence of unintended introductions of Phytophthora species into native habitats has recently increased in prevalence in Northern California. There is a lack of baseline data on Phytophthora diversity in other ecosystems, such as those present in Southern California. To better understand Phytophthora distribution and the risk it poses to native habitats, from 2018-2021, soil samples were collected from Angeles National Forest (ANF) lands in Southern California (Los Angeles County). Forty sites were surveyed, and soil samples were taken from plant rhizospheres, riverbeds and off-road vehicle tracks in chaparral and oak woodland areas. From these surveys, fourteen species of Phytophthora were detected, including three undescribed and one hybrid species: P. cactorum (clade 1a), P. multivora (clade 2c), P. inundata and P. rosacearum (clade 6a), P. chlamydospore, P. crassamura, P. gonapodyides, P. lacustris, P. lacustris x riparia, P. megasperma, P. taxon pocumtuck and P. riparia (clade 6b), P. sp. cadmea (clade 7a) and P. taxon oakpath (clade 8e); the latter two provisional species are introduced herein and phylogenetically characterized and. Phytophthora species detected in rhizosphere soil were found underneath both symptomatic and asymptomatic plants and were most frequently associated with Salvia mellifera, Quercus agrifolia and Salix spp. Phytophthora species were found in both chaparral and oak woodlands, primarily in riparian areas, including detections in off-road tracks, trails, and riverbeds. Although these Mediterranean ecosystems are amongst the driest and most fire prone areas in the United States, they harbor a large diversity of Phytophthora species, indicating a potential risk for disease for the native Californian vegetation.