Phytophthora Community Structure Analyses in Oregon Nurseries Inform Systems Approaches to Disease Management

To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by the American Phytopathological Society and can be found at: http://apsjournals.apsnet.org/loi/phyto.Nursery plants are important vectors for plant pathogens. Understanding\ud what pathogens occur in nurseries in different production stages\ud can be useful to the development of integrated systems approaches. Four\ud horticultural nurseries in Oregon were sampled every 2 months for 4 years\ud to determine the identity and community structure of Phytophthora spp.\ud associated with different sources and stages in the nursery production\ud cycle. Plants, potting media, used containers, water, greenhouse soil, and\ud container yard substrates were systematically sampled from propagation\ud to the field. From 674 Phytophthora isolates recovered, 28 different\ud species or taxa were identified. The most commonly isolated species from\ud plants were Phytophthora plurivora (33%), P. cinnamomi (26%), P.\ud syringae (19%), and P. citrophthora (11%). From soil and gravel\ud substrates, P. plurivora accounted for 25% of the isolates, with P. taxon\ud Pgchlamydo, P. cryptogea, and P. cinnamomi accounting for 18, 17, and\ud 15%, respectively. Five species (P. plurivora, P. syringae, P. taxon\ud Pgchlamydo, P. gonapodyides, and P. cryptogea) were found in all\ud nurseries. The greatest diversity of taxa occurred in irrigation water\ud reservoirs (20 taxa), with the majority of isolates belonging to internal\ud transcribed spacer clade 6, typically including aquatic opportunists.\ud Nurseries differed in composition of Phytophthora communities across\ud years, seasons, and source within the nursery. These findings suggest likely\ud contamination hazards and target critical control points for management\ud of Phytophthora disease using a systems approach