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ARS Home » Pacific West Area » Corvallis, Oregon » Horticultural Crops Disease and Pest Management Research Unit » Research » Publications at this Location » Publication #420322
Research Project: Knowledge Based Tools for Exotic and Emerging Diseases of Small Fruit and Nursery Crops

Location: Horticultural Crops Disease and Pest Management Research Unit

Title: First report of phytophthora ramorum causing leaf spot on arbutus × reyorum ‘Marina’ in the United States

Author
item DEUITCH, E.M - University Of California, Davis
item ROONEY-LATHAM, S - California Department Of Food And Agriculture
item BLOMQUIST, C - California Department Of Food And Agriculture
item BELISLE, W - California Department Of Food And Agriculture
item SORIANO, M - (NCE, CECR)networks Of Centres Of Exellence Of Canada, Centres Of Excellence For Commercilization A
item Grunwald, Niklaus

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/29/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary: The Marina Strawberry tree is a popular ornamental evergreen species, prized for its glossy evergreen foliage, display of pink and white bell-shaped blooms, and strawberry-like ornamental fruits. An infect leaf sample from a Humboldt County, California nursery was submitted for inspection at the California Department of Food and Agriculture Plant Pest Diagnostic Laboratory showing symptoms of leaf necrosis. We isolated the pathogen and identified it by gene sequencing. We also reinfected Marina Strawberry plants to confirm that the pathogen causes the symptoms observed and reisolated that pathogen in culture from symptomatic plants. Our work confirms that the sudden oak death pathogen P. ramorum is causing disease on Marina strawberry. To the best of our knowledge this represents the first report of P. ramorum infecting Marina Strawberry trees. P. ramorum is a devastating disease affecting a wide array of plants across many environments.

Technical Abstract: he Marina Strawberry tree (Arbutus × reyorum Demoly. ‘Marina’) is a popular ornamental evergreen species, prized for its glossy evergreen foliage, display of pink and white bell-shaped blooms, and strawberry-like ornamental fruits. In April 2024, a foliar sample from a Humboldt County, California nursery was submitted to the CDFA Plant Pest Diagnostic Laboratory showing symptoms of marginal leaf necrosis. We isolated the pathogen on selective media and subsequently identified it by sequencing the ITS ad cox1 region as Phytophthora ramorum. Based on microsatellite analysis, the isolate was placed within the NA2 clonal lineage. Koch’s postulates were performed to confirm pathogenicity using Arbutus × reyorum ‘Marina’ trees. P. ramorum was consistently isolated from symptomatic foliage of the inoculated plants, while no symptoms were observed in the control group and no Phytophthora was isolated. Although Arbutus unedo and A. menziesii are known hosts for P. ramorum, to our knowledge, this represents the first report of P. ramorum infecting Arbutus × reyorum ‘Marina’. P. ramorum is a devastating disease affecting a wide array of plants across many environments. The identification of this new host presents a potential risk for the spread of the disease between susceptible hosts within nurseries and landscapes.