Linking ecology and plant pathology to unravel the importance of soil-borne fungal pathogens in species-rich grasslands

Soil-borne fungal diseases are a major problem in agriculture. A century ago, the Dutch plant pathologist Johanna Westerdijk recognized the importance of linking fungal biology with ecology to understand plant disease dynamics. To explore new ways to manage soil-borne fungal disease in agriculture by learning from nature', we follow in her footsteps: we link below ground plant-fungal pathogen interactions to ecological settings, i.e. natural grasslands. Ecological research hypothesised that the build-up of enemies' is reduced in species-rich vegetation compared to monocultures. To understand how plant diversity can suppress soil-borne fungal pathogens, we first need to identify fungal actors in species-rich grasslands. Next-generation sequencing revealed a first glimpse of the potential fungal actors, but their ecological functions often remain elusive. Databases are becoming available to predict the ecological fungal guild, but classic phytopathology studies that isolate and characterize - taxonomically and functionally -, remain essential. Secondly, we need to set-up experiments that reveal ecological mechanisms underlying the complex below ground interactions between plant diversity and fungal pathogens. Several studies suggested that disease incidence of (host-specific) pathogens is related to abundance of the host plant species. However, recent studies suggest that next to host species density, presence of heterospecific species additionally affects disease dynamics. We explore the direct and indirect ways of these neighboring plants diluting pathogen pressure. We argue that combining the expertise of plant pathologists and ecologists will improve our understanding of belowground plant-fungal pathogen interactions in natural grasslands and contribute to the design of sustainable and productive intercropping strategies in agriculture.