P-311 - Blumeria hordei induces barley susceptibility to secondary fungal infections

Plants are colonized by a diverse set of microbes. Here, we investigate how the infection of barley with the obligate biotrophic powdery mildew fungus Blumeria hordei (Bh) affects secondary infections by cereal pathogens that have a major economic and agricultural impact. Using time-resolved co-infection experiments, we demonstrate that primary Bh infection significantly promotes infection, biomass and disease symptoms of multiple hemibiotrophic fungi, including Zymoseptoria passerinii, Magnaporthe oryzae, and Bipolaris sorokiniana. Interestingly, we did not detect the same effect on bacterial colonizers of barley suggesting a specific effect of Bh on secondary infections of adapted fungal phytopathogens. Surprisingly, the common barley cultivar Golden Promise, which is resistant to B. sorokiniana leaf infection becomes fully susceptible to B. sorokiniana-mediated leaf spot disease in the presence of Bh. Our time-resolved approach demonstrates that the mechanism underlying this Bh-induced susceptibility is dependent on the sequence of infection by the two fungi. In turn, Bh does not positively affect B. sorokiniana-mediated root rot. Together these observations suggest a positive local effect of Bh on secondary fungal infections of the barley host. Future work will explore the molecular mechanisms underlying these effects with the aim to elucidate the complex infection dynamics that can have implications for disease management.