Fungal Endophytes are Involved in Multiple Balanced Antagonisms

In order for endophytic fungi to grow asymptomatically in their plant hosts, a balance of antagonisms is presumed to exist between host defence and fungal virulence. However, in planta, endophytic fungi must deal with multiple organismal interactions, primarily with bacteria and other fungi. We hypothesize that the plethora of antibacterial and antifungal metabolites that endophytic fungi produce has the function of maintaining balances of antagonisms with microbial competitors, resulting in a compatible multipartite symbiosis. Results obtained from co-cultures of endophytic and rhizospheric fungi with Pseudomonas aeruginosa and of endophytic fungi with Hymenoscyphus fraxineus, pathogen of the European ash, corroborate this hypothesis.