Skip to main content
ARS Home » Pacific West Area » Corvallis, Oregon » Horticultural Crops Disease and Pest Management Research Unit » Research » Publications at this Location » Publication #373219

Research Project: Development of Knowledge-based Approaches for Disease Management in Small Fruit and Nursery Crops

Location: Horticultural Crops Disease and Pest Management Research Unit

Title: Pathogenicity of four phytophthora species causing rhododendron root rot in Oregon

item SACHER, GABRIEL - Oregon State University
item Scagel, Carolyn
item Davis, Elizabeth
item Beck, Bryan
item Weiland, Jerry

Submitted to: Journal of Plant Health
Publication Type: Abstract Only
Publication Acceptance Date: 4/3/2020
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Phytophthora root rot is a destructive disease of rhododendron, causing substantial losses in infested fields and container production areas of this important ornamental nursery crop. Historically, Phytophthora cinnamomi was considered the main causal agent of the disease. However, a recent survey of soilborne Phytophthora species from symptomatic rhododendrons in Oregon revealed that P. plurivora is now more abundant than P. cinnamomi and that several other less common Phytophthora species are also involved. We investigated the ability of the four most abundant species identified from the survey to cause root rot: P. plurivora, P. cinnamomi, P. cryptogea, and P. pini. We infested the soil of containerized Rhododendron catawbiense ‘Boursault’ in a greenhouse experiment using three to four isolates of each species obtained from six Oregon nurseries. Each species caused root rot, with P. plurivora, P. cinnamomi, and P. pini causing frequent, severe symptoms (= 90% incidence of severe root rot) and P. cryptogea causing fewer, less severe symptoms (46% incidence of severe root rot). Little difference was observed between isolates of the same species. Results show that these four Phytophthora species, which were representative of 86% of the isolates from the survey, are capable of causing significant damage but that not all species are equally pathogenic. Further research on Phytophthora root rot of rhododendron should consider whether the efficacy of disease control strategies, such as host resistance and chemical control, differ among the causal agents of this disease.