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Abstract Background and aimsPlant interactions with soil microbial communities are critical for understanding plant health, improving horticultural and agricultural outcomes, and maintaining diverse natural communities. In some cases, disease suppressive soils enhance plant survival in the presence of pathogens. However, species-specific differences and seasonal variation complicate our understanding of the drivers of soil fungal communities and their consequences for plants. Here, we aim to describe soil fungal communities acrossRhododendronspecies and seasons as well as the test for fungal indicators ofRhododendronspecies in the soil. Further, we test possible mechanisms governing disease suppressive soils to the oomycete pathogenPhytophthora cinnamomi. Variation in disease susceptibility to this pathogen across species and clades allows us to test for possible fungal drivers of disease suppressive soils. MethodsWe conducted high throughput sequencing of the fungal communities found in soil collected under 14Rhododendronspecies and across 2 seasons (April, October) at two sites in Ohio, USA. Phylogenetic analyses were used to ask whether fungal community composition correlated with increased plant survival with the addition of whole soil communities from a prior greenhouse experiment. ResultsEffects ofRhododendronspecies (R² = 0.13), season (R² = 0.01) and their interaction on fungal communities (R² = 0.11) were statistically significant. Fungal community composition negatively correlated with survival following exposure to whole soil microbial communities, though this result depended on the presence ofR. minus. Forty-fiveTrichodermataxa were identified across our soil samples, and someTrichodermawere significantly associated with particularRhododendronspecies (e.g.Trichoderma atroviridewas associated withR. molle) in indicator species analyses. ConclusionThe correlation between plant responses to soil biotic communities and fungal community composition, as well as the presence of potential beneficial taxa such asTrichodermaand mycorrhizal fungi, are consistent with fungal-mediated survival benefits from the pathogenPhytophthora cinnamomi. 

Background and aims Plant interactions with soil microbial communities are critical for understanding plant health, improving horticultural and agricultural outcomes, and maintaining diverse natural communities. In some cases, disease suppressive soils enhance plant survival in the presence of pathogens. However, species-specific differences and seasonal variation complicate our understanding of the drivers of soil fungal communities and their consequences for plants. Here, we aim to describe soil fungal communities across Rhododendron species and seasons and as well as the test for fungal indicators of species and seasons in the soil. Further, we tested for correlations between fungal community composition and prior experimental quantification of disease suppressive soils. Methods We conducted high throughput sequencing of the fungal communities found in soil collected under 14 Rhododendron species and across 2 seasons (April, October) at two sites in Ohio, USA. We described these soils and used phylogenetic analyses to ask whether fungal community composition correlated with increased plant survival with the addition of whole soil communities from a prior greenhouse experiment. Results We found effects of Rhododendron species and season on fungal communities. Fungal community composition correlated with survival following exposure to whole soil microbial communities, though this result depended on the presence of R. minus. We identified 45 Trichoderma taxa across our soil samples, and some Trichoderma were significantly associated with particular Rhododendron species in indicator species analyses. Conclusion The correlation between plant responses to soil biotic communities and fungal community composition, as well as the presence of potential beneficial taxa such as Trichoderma and mycorrhizal fungi, are consistent with fungal-mediated survival benefits from the pathogen Phytophthora cinnamomi.