Fungal communities driven by Rhododendron species correlate with pathogen protection against Phytophthora 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.