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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 #380605
Research Project: Integrated Disease Management of Exotic and Emerging Plant Diseases of Horticultural Crops

Location: Horticultural Crops Disease and Pest Management Research Unit

Title: First reports of phytophthora ramorum clonal lineages NA1 and EU1 from tanoaks in Del Norte county, California

Author
item GARBELOTTO, M - University Of California
item SCHMIDT, D - University Of California
item DOVANA, F - University Of California
item LEE, C - California Department Of Forestry And Fire Protection(CAL FIRE)
item FIELAND, V - Oregon State University
item Grunwald, Niklaus - Nik
item VALACHOVIC, Y - University Of California - Cooperative Extension Service

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2021
Publication Date: 1/18/2021
Citation: Garbelotto, M., Schmidt, D., Dovana, F., Lee, C., Fieland, V.J., Grunwald, N.J., Valachovic, Y. 2021. First reports of phytophthora ramorum clonal lineages NA1 and EU1 from tanoaks in Del Norte county, California. Plant Disease. https://doi.org/10.1094/PDIS-12-20-2633-PDN.
DOI: https://doi.org/10.1094/PDIS-12-20-2633-PDN

Interpretive Summary: Phytophthora ramorum is a plant pathogen causing the sudden oak death disease on the US West coast. In the US, this pathogen exists as 3 genetically distinct lineages called NA1, NA2 and EU1. Recent forest health surveys led to new detections of P. ramorum in Del Norte County, California. This is the first report of the occurrence of sudden oak death in Del Norte county. The 2019 finding belonged to the NA1 lineage, whereas as the 2020 finding belonged to the EU1 lineage. This is the first time the EU1 lineage is found in CA forests. These findings indicate that the pathogen continues to invade new forest areas.

Technical Abstract: An intensive year of forest health surveys has led to the first two detections of Phytophthora ramorum in Del Norte County and to the first wildland detection of the EU1 clonal lineage in California. In July 2019, leaves were sampled from two tanoaks and 16 California bay laurels in Jedediah Smith State Park in Del Norte County, California. All leaves displayed black lesions normally associated with Sudden Oak Death (SOD) caused by P. ramorum. Samples were surface sterilized using 75% Ethanol and plated on VARPH medium. After plating, DNA was extracted from leaves using the ROSE protocol. DNA extracts were amplified using PCR primers from two P. ramorum specific assays including the ITS and the Cox-I assays. Only leaves from the two tanoaks gave positive PCR results and yielded cultures with colony morphology, sporangia and chlamydospores typical of the NA1 lineage of P. ramorum. The ITS locus and a portion of the Cox I locus were sequenced from DNA extracts of cultures amplified using primers ITS4-DC6 and COXF4N-COXR4N, respectively. The two ITS sequences (GB accessions MN540639 and MN540640) and the two Cox I sequences (GB accessions MN540142 and MN540143) were a perfect match for the NA1 lineage. Microsatellite genotyping was conducted to determine multilocus genotype (MLG). The two Del Norte MLGs were identical to one another and were most similar to MLG c1, with a single repeat difference at a single locus. The SSR results suggest the inoculum source may not be from neighboring Humboldt County, but from a yet unidentified outbreak, possibly associated with infected ornamental plants. Jedediah Smith State Park and surrounding forests were surveyed for 12 months following the initial detection, and the pathogen has yet to be re-detected at and around that site. In July 2020, symptomatic leaves from two tanoak trees were collected 5 miles north of Jedediah Smith State Park where three tanoak trees had recently died, and samples were processed as above. Colonies from these samples produced chlamydospores and sporangia typical of P. ramorum on VARPH medium, but displayed a growth rate faster than that of NA1 genotypes and were characterized by aerial hyphae, overall resembling the morphology of EU1 lineage colonies. The EU1 lineage was confirmed by sequencing a portion of the cellulose binding elicitor lectin gene. The EU1 clonal lineage has been previously described in Oregon forests, approximately 35 miles to the North, but this is the first report for California wildlands.