ARS | Publication request: Population structure and genetic diversity of three species of Pythium isolated from forest tree nursery soils in Oregon and Washington

Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: June 1, 2012
Publication Date: July 1, 2012
Citation: Garrido, P., Garzon, C., Grunwald, N.J., Weiland, G.E. 2012. Population structure and genetic diversity of three species of Pythium isolated from forest tree nursery soils in Oregon and Washington. Phytopathology. 515.

Technical Abstract: The genus Pythium includes some of the most important soilborne pathogens that cause damping–off and root rot of conifers, resulting in high seedling mortality in forest tree nurseries. The aim of this study was to analyze the diversity and population structure of three species of Pythium (P. irregulare, P. sylvaticum, and P. ultimum) isolated from soil at three forest nurseries in Oregon and Washington. Three molecular marker methods were used: Inter Simple Sequence Repeat (ISSR), Simple Sequence Repeats (SSR), and Amplified Fragment Length Polymorphisms (AFLP). AMOVA, based on geographic distribution, identified significant genetic differences among nursery populations of P. sylvaticum and P. irregulare, whereas no significant differences among P. ultimum populations were found. Isolate distribution by Principal Coordinate analysis and UPGMA were congruent among methods, but provided no clear evidence of geographically-defined populations in either species. Instead, significant intraspecific differentiation, unrelated to nursery of origin, was detected in P. irregulare (2 groups), P. sylvaticum (3 groups), and P. ultimum (2 groups). The evolutionary processes determining the population structure observed in the samples of these species remain to be determined. Their discovery may provide useful information for disease prevention and management of Pythium diseases in forest nurseries.