Comparison of the Species Communities of Phytophthora, Pythium, and Phytopythium Associated with Soybean Genotypes in High Disease Environments in Ohio

The roles that specific cultivars with different levels and types of resistance may play on the diversity and abundance of Phytophthora, Phytopythium, and Pythium spp. communities were compared. Three soybean cultivars were planted in a total of 11 different high disease environments in Ohio and seedlings were collected for direct isolation and amplicon sequencing of the rhizosphere soil. Plant population and yields were lower for the moderately susceptible cultivar Sloan compared with the cultivars Kottman, with high partial resistance to Phytophthora sojae, and Lorain, with high partial resistance to both Pythium spp. and Phytophthora sojae. Based on both direct isolation and amplicon sequencing, distinct communities with key indicator species were identified at each environment, including differences at 14 and 25 day after planting for two environments. The environment had the largest influence on the community composition. Soybean genotype did influence the abundance of the hemibiotroph Phytophthora sojae but not species of Phytopythium or Pythium. In addition, from all environments and cultivars, operational taxonomic units (OTUs) classified as Pythium attrantheridium, P. heterothallicum, and P. sylvaticum were always detected. This is also the first report of an OTU of P. periilum from soils and the first one to recover undescribed species that match the sequence of Pythium sp. CAL2011f from soybean seedlings in Ohio This study highlights which species to target for the identification and development of resistant cultivars or for fungicide screening.