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ARS Home » Pacific West Area » Corvallis, Oregon » Horticultural Crops Research Unit » Research » Publications at this Location » Publication #305423
Title: Population structure of Pythium irregulare, P. sylvaticum, and P. ultimum in forest nursery soils of Oregon and Washington

Author
item Weiland, Gerald - Jerry
item GARRIDO, PATRICIA - Oklahoma State University
item KAMVAR, ZHIAN - Oregon State University
item MAREK, STEPHEN - Oklahoma State University
item Grunwald, Niklaus - Nik
item GARZON, CARLA - Oklahoma State University

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/18/2014
Publication Date: 5/1/2015
Citation: Weiland, G.E., Garrido, P., Kamvar, Z.N., Marek, S.M., Grunwald, N.J., Garzon, C.D. 2015. Population structure of Pythium irregulare, P. sylvaticum, and P. ultimum in forest nursery soils of Oregon and Washington. Phytopathology. 105(5):684-694.

Interpretive Summary: Pythium species are important soilborne pathogens occurring in the forest nursery industry of the Pacific Northwest. We examined the genetic diversity and population structure of 115 isolates of Pythium irregulare, P. sylvaticum, and P. ultimum to determine whether there was evidence that these pathogens have been moved among three forest nurseries on seedlings or on shared field equipment. We found that there is evidence that these pathogens have been moved from nursery to nursery because isolates with the same genotype were found at more than one location. This information is important because new pathogen species or fungicide-resistant isolates can accidentally be moved into locations where they had not occurred previously and potentially cause new disease outbreaks.

Technical Abstract: Pythium species are important soilborne pathogens occurring in the forest nursery industry of the Pacific Northwest. However, nothing is known about their genetic diversity or population structure and it is suspected that isolates are moved among forest nurseries on seedling stock and shared field equipment. In order to address these concerns, 115 isolates of three Pythium species (P. irregulare, P. sylvaticum, and P. ultimum) were examined at three forest nurseries using simple sequence repeat (SSR) and amplified fragment length polymorphism (AFLP) markers. Analyses revealed distinct patterns of intraspecific variation for the three species. P. sylvaticum exhibited the most diversity, followed by P. irregulare, and substantial clonality was found in P. ultimum. At least two groups were found within each species. For both P. irregulare and P. sylvaticum, but not P. ultimum, there was evidence for significant variation among nurseries as well as intrinsic structure not associated with nursery. Evidence of movement of isolates of the three species among nurseries was found. Evidence that certain lineages and clonal genotypes are shared among all three nurseries indicates that pathogen movement from location to location has occurred.