The Effect of Incubation Temperature on the Species Composition of Phytophthora, Phytopythium, and Pythium Communities Associated with Soybean

Multiple species of Phytophthora, Phytopythium, and Pythium cause detrimental effects to soybean and more than one species have often been recovered from symptomatic soybean seedlings or roots, suggesting that these occur as species complexes. Our objective was to assess the species diversity and abundance of Phytophthora, Phytopythium, and Pythium spp. associated with soybean seedlings at two different incubation temperatures from soils collected from the same 81-ha farm but from five fields with a different history of production practices. To determine the effect of incubation temperature on the species detected, soils were baited with soybean seedlings at 15 and 25°C. At each temperature, isolates were directly recovered from seedling roots and the associated rhizosphere soil was assayed via amplicon sequencing with oomycete-specific primers. Regardless of incubation temperature or field site, the species Pythium sylvaticum and Pythium ultimum were isolated through the baiting procedure and these, along with Pythium acrogynum, Pythium attrantheridium, and Pythium heterothallicum, were detected with amplicon sequencing. Some Pythium spp. were more abundant at 15°C while others were favored at 25°C. This study demonstrated that the species diversity of Phytophthora, Phytopythium, and Pythium detected on seedling roots and in the rhizosphere of soybean can be influenced by incubation temperature. This may explain, in part, the differences in the species composition reported from previous surveys and suggests that production practices associated with each of the sampled fields may have influenced the species complexes of Phytophthora, Phytopythium, and Pythium.