Host-specific fungal plant pathogens exhibit distinct interactions with the leaf microbiota of wild grasses

The plant's microbiome is influenced by the plant species and biotic factors such as infection by pathogens. Pathogen-microbiome interactions are relevant for disease progression since both can compete within the host. We hypothesize that pathogens specialized to different hosts have distinct, direct and indirect influence on the host microbiome. We focused on the host-specific leaf pathogens Zymoseptoria tritici and Zymoseptoria passerinii. By using microbiome metabarcoding and coculture interactions, we evaluated the influence of virulent (wild host-infecting pathogen) and avirulent (domesticated host-infecting pathogen) Zymoseptoria isolates on the leaf microbiome of the wild grasses Aegilops cylindrica and Hordeum murinum, which are hosts to virulent lineages of Z. tritici and Z. passerinii, respectively. Our microbiome analysis showed that the fungal communities were affected by virulent lineages, while the avirulent lineages had the most negative correlations with bacteria. Both virulent and avirulent pathogens had a similar spectrum of interactions when experimentally cocultured with bacteria. The intensity of pathogen-induced growth enhancement on bacteria differed between Z. tritici isolates. We demonstrated that the pathogen-secreted invertases can be a determinant of bacterial growth enhancement. Our study illustrates the extent of specificity in pathogen-microbe coexistence and suggests an interaction mechanism that may influence in planta interactions. This article is part of the theme issue 'Wild plant pathosystems'.