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

Abstract

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 as well as the test for fungal indicators of Rhododendron species in the soil. Further, we test possible mechanisms governing disease suppressive soils to the oomycete pathogen Phytophthora cinnamomi. Variation in disease susceptibility to this pathogen across species and clades allows us to test for possible fungal drivers 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. 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.

Results

Effects of Rhododendron species (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 of R. minus. Forty-five Trichoderma taxa were identified across our soil samples, and some Trichoderma were significantly associated with particular Rhododendron species (e.g. Trichoderma atroviride was associated with R. molle) 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.