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ARS Home » Pacific West Area » Corvallis, Oregon » Horticultural Crops Research Unit » Research » Publications at this Location » Publication #310840
Title: Diversity of foliar Phytophthora species on Rhododendron in Oregon nurseries

Author
item Knaus, Brian
item FIELAND, VALERIE - Oregon State University
item Graham, Kimberly
item Grunwald, Niklaus - Nik

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/25/2015
Publication Date: 8/11/2015
Citation: Knaus, B.J., Fieland, V.J., Graham, K., Grunwald, N.J. 2015. Diversity of foliar Phytophthora species on Rhododendron in Oregon nurseries. Plant Disease. 99(10):1326-1332. https://doi.org/10.1094/PDIS-09-14-0964-RE.
DOI: https://doi.org/10.1094/PDIS-09-14-0964-RE

Interpretive Summary: Organisms in the genus Phytophthora include many important plant pathogens. Perhaps most important to nursery growers in the Pacific Northwest is the causative agent of sudden oak death. This organism is quarantined by the federal government. Nurseries which test positive for this organism typically need to destroy large amounts of plant material in order to avoid spreading the pathogen, an act which typically results in a large financial loss for the nursery. Unfortunately, lesions caused by this regulated pathogen look very similar to lesions caused by other species in the genus which are not regulated. It is therefore important to know what species of this pathogen typically occur in nurseries and with what frequency this quarantined taxon occurs. We surveyed nurseries in the US state of Oregon to determine which species occur frequently and which are uncommon with a special focus on the quarantined species. During this work we also developed a rapid and inexpensive diagnostic assay to determine which species have been sampled. Our results identified two species as abundant and nine others which were rare. None of our samples tested positive for the quarantined species. This information can be used by nursery growers to help determine which species in this genus they may expect to find in their nurseries and inform regulators as to how well the quarantined species has been managed.

Technical Abstract: The genus Phytophthora is considered to contain some of the most important plant pathogens affecting nursery crops. Given the recent emergence of the sudden oak death pathogen P. ramorum, particularly in association with Rhododendron, it has become prudent to characterize Phytophthora communities in nursery environments. Many taxa may present syptoms similar to regulated taxa and may vary in pathogenicity from regulated taxa, making determination important. We present a survey of Phytophthora taxa observed from seven nurseries in the U.S. state of Oregon. Incidence and diversity of Phytophthora communities differed significantly among nurseries and among seasons within nursery. The taxa P. syringae and P. plurivora were widespread and detected at most of the nurseries sampled. Nine other taxa were also detected but were found either in a single nursery or were shared among only a few nurseries. Charactertization of the Phytophthora communities present in nurseries is an important step towards understanding the ecology of these organisms as well as an aid to nursery managers in determining what risks may be present when symptomatic plants are observed. This study builds on an increasing literature which characterize Phytophthora community structure in nurseries.