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ARS Home » Pacific West Area » Corvallis, Oregon » Horticultural Crops Research » Research » Publications at this Location » Publication #242098

Title: Pythium species Associated with Forest Tree Nurseries of Oregon and Washington

item Weiland, Jerry

Submitted to: International Union Of Forestry Research Organization
Publication Type: Abstract Only
Publication Acceptance Date: 6/30/2009
Publication Date: 7/12/2009
Citation: Weiland, G.E. 2009. Pythium species Associated with Forest Tree Nurseries of Oregon and Washington. International Union Of Forestry Research Organization Book of Abstracts.

Interpretive Summary:

Technical Abstract: Pythium species are one of several pathogen genera responsible for damping off of conifer seedlings in forest tree nurseries. Species identification has been traditionally based on morphology. However, DNA-based identification methods may allow more accurate identification of species associated with disease. Field trials were established in 2008 at three nurseries (2 in OR, 1 in WA) to: 1) evaluate the impact of fumigation on Pythium soil populations; and 2) identify Pythium species associated with damping off. Six fumigant treatments (including a conventional methyl bromide treatment and a nonfumigated control) were applied according to a randomized complete block design with four blocks at each nursery. Soil samples were collected before and after fumigation and Pythium populations were assessed by baiting with rhododendron leaves and douglas fir needles and by dilution plating onto PARP, a semiselective medium for pythiaceous species. Prior to fumigation, populations in nonfumigated control plots were 9 CFU/g soil at nurseries A and C and 14 CFU/g soil at nursery B. One month after fumigation, populations in the same control plots were greatest at nursery B (8 CFU/g soil), intermediate at nursery A (5 CFU/g soil), and least at nursery C (1 CFU/g soil). Populations were similar seven months after fumigation. All fumigant treatments reduced soil populations by at least 68%. Isolates are currently being identified on the basis of DNA sequence from the internal transcribed spacer (ITS) region. Three species (Pythium macrosporum, P. irregulare and P. dissotocum) are predominate at all three nurseries.