Diversity of oomycetes associated with soybean seedling disease in the U.S.

<p>Oomycete pathogens of soybean (Glycine max) result in low stand establishment and root rot often reducing yield. There is limited information regarding abundance and diversity of oomycetes species across most soybean producing states. A two-year survey was conducted across 11 states to determine diversity of oomycetes associated with soybean seedling diseases. In 2011, a total of 2400 isolates were collected on the semi-selective medium (CMA-PARP+B). In 2012, a second semi-selective medium (V8+RPBH) was included, but due to drought and limited symptomatic fields the number of recovered isolates was 1100. Isolates were identified using the ITS region of rDNA and GIS data was used to find association between species and environmental data. In 2011, preliminary sequence results distinguished a total of 52 Pythium, 2 Phytopythium and 3 Phytophthora spp., with Py. sylvaticum (16%) and Py. oopapillum (12%) being the most frequently recovered. In 2012, a total of 57 Pythium spp., 7 Phytophthora spp., and 4 Phytopythium were found, with Py. sylvaticum (15%) and Py. heterothallicum (13%) species being most abundant. Oomycete species composition frequency was noted to fluctuate greatly; the resulting species diversity was correlated with latitude and temperature gradients. Seed and seedling rot assays were conducted to determine the pathogenicity and virulence of the different species. This study will serve as the foundation for the development of diagnostic tools and the improvement of soybean seedling and root health.