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Ecological significance of soybean seed treatments on oomycete communities

Zachary Noel: Michigan State University

<div>Seedling diseases caused by <em>Phytophthora </em>spp., <em>Pythium </em>spp. and <em>Phytopythium </em>spp. pose a significant threat to soybean production. To manage loss due to pests and diseases, seeds are commonly coated with treatments containing fungicides and insecticides. However, not much is known about the ecological significance of chemical seed treatments on oomycete communities. We used amplicon sequencing to investigate the ecological dynamics of oomycete communities in soybean rhizosphere soils. The hypothesis was that seed treatments would act as community filters selecting for specific oomycete populations. Rhizosphere soils were collected, in Michigan, over two years from two locations from soybean seedlings treated with commercially relevant fungicides, insecticides and nematicides and sequenced using Illumina MiSeq. Preliminary analyses indicate that alpha and beta diversity was not highly influenced by seed treatments or soybean varieties; however, composition (β diversity) was highly structured by location, indicating that the effects of seed treatment may be subtle and location specific. For example, in one location, indicator species analysis showed that <em>Pythium hypogynum </em>was significantly more abundant in rhizosphere soils of seedlings treated with a combination of fungicides and <em>Pythium hydnosporum </em>was significantly less abundant in samples treated with fungicides and an insecticide. Investigations into other ecological processes in controlled growth chamber studies are currently being used to study oomycete assembly onto treated soybean seeds/seedlings.</div>