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Ecology and evolution of oomycete communities in response to soybean seed treatments

Zachary Noel: Michigan State University

<div>Soil conservation efforts combined with earlier planting dates has led to increased crop residue and cooler soil at planting. This exposes seeds and developing seedlings to adverse conditions for extended periods of time. To gain a better understanding of soybean seed treatments as oomycete community filters, culture based techniques, evolutionary analysis and genetics are utilized. A high-throughput assay was developed and applied to evaluate the fungicide sensitivity of 81 oomycete species across ten clades to ethaboxam and mefenoxam. Species within three separate <em>Pythium </em>clades all had reduced sensitivity to ethaboxam, suggesting that reduced sensitivity to ethaboxam is inherent and possibly related phylogenetically. Therefore, the evolutionary relationship of ethaboxam sensitivity was investigated. Bayesian phylogenetics and ancestral sequence reconstruction of <em>Pythium</em> β-tubulin gene trees indicated that species with reduced sensitivity to ethaboxam followed a convergent evolutionary pattern, and had evolved three separate times under two transversion mutations. Heterologous expression of <em>Pythium </em>β-tubulin in a yeast model system is being used to determine the molecular mechanism of ethaboxam resistance. However, the ecological dynamics of seed treatments on oomycete communities remain difficult to explain. Based on preliminary investigations on isolation and amplicon sequencing data from roots and rhizosphere soils, filtering based on seed treatment chemistry may be subtle and location specific. Currently, other ecological dynamics in combination with seed treatments are being investigated with amplicon sequencing. This information will enhance management of seedling diseases caused by oomycetes in the Midwest.</div>