Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/20/2003
Publication Date: 7/20/2003
Citation: PAULITZ, T.C., ADAMS, K.J. COMPOSITION AND DISTRIBUTION OF PYTHIUM COMMUNITIES FROM WHEAT FIELDS IN EASTERN WASHINGTON STATE.. PHYTOPATHOLOGY. 2003. Interpretive Summary: Thirteen species of Pythium have been isolated from wheat soils collected from 80 sites in eastern Washington. Pythium species cause seedling and root rot on wheat and barley. These include at least one new species (P. abappressorium), one putative new species, and 2 new records. The distribution and frequency of Pythium communities across eastern Washington over a range of soil types, rainfall, and temperatures was investigated.
Technical Abstract: Pythium spp. were isolated from the soil of 80 wheat fields in eastern Washington in summer 2000, from an area encompassing approximately 27,000 km2. These sites covered a range of soil textures (course to fine silty loess), average annual precipitation (200 to 600 mm) and average annual temperatures (7 to 11 C). Soil type and annual precipitation run in an east-west gradient, while temperature has a north-south gradient. Species were identified using classical methods and by sequencing the ITS-1 region of the rDNA and comparing these sequences to a database from a world-wide collection of Pythium spp. The most prevalent species and frequency of occurrence in sites were P. abappressorium sp. nov. (A)(50%), P. rostratum (R)(40%), P. debaryanum (D)(37.5%), P. heterothallicum (H)(33.7%), P. oligandrum (O)(31.2%), an unidentified P. sp. (aff. echinulatum) (E)(25%), and P. ultimum (U)(18%). P. intermedium, P. irregulare, P. paroecandrum, P. sylvaticum, P. dissimile, and P. dissoticum were isolated at a low frequency. From one to six species were isolated at each site, and there were 46 different species combinations detected. The species presence/absence data from all sites were analyzed with Jaccard's Similarity Coefficient hierarchical cluster analysis. Six communities were identified (species within each community in order of dominance)- AD, AOU, AR, DEH, HE, and RU. In general, P. abappressorium was evenly distributed over all zones. AOU was more prevalent in zones with lower precipitation and courser soil, while DEH and HE were associated with zones with higher precipitation and finer-textured soils, based on comparison of frequency distributions with the expected distribution over all the sites. The RU community was more prevalent at higher temperature zones. Canonical correspondence analysis was performed to examine the relationship between species and environmental variables. Soil type and precipitation were highly correlated with each other and with axis 1, which separated P. ultimum and P. abappressorium (lower variable values) from P. heterothallicum (higher variable values). Axis 2 and 3 were most correlated with temperature, and these axes separated P. oligandrum (higher value) from P. debaryanum (lower value) and P. ultimum-P. rostratum from the other species. Species composition, distributions and associations may be influenced by environmental factors at a mesoscale level (100-1,000,000 ha) .