Soil microbes mediate the effects of nitrogen supply and co-inoculation on Barley Yellow Dwarf Virus in Avena sativa

O_LINutrient supply rates to hosts can mediate host-pathogen interactions. In terrestrial systems, nutrient supply to plants is mediated by soil microbes, suggesting a potential indirect effect of soil microbes on plant-pathogen interactions. Soil microbes also may affect plant pathogens by inducing plant defenses. C_LIO_LIWe tested the role of soil microbes, nitrogen supply to plant hosts, and co-inoculation on infection by aphid-vectored RNA viruses, Barley Yellow Dwarf Virus (BYDV-PAV) and Cereal Yellow Dwarf Virus (CYDV-RPV), in a grass host grown in soil microbes collected from a long-term nitrogen enrichment experiment. C_LIO_LIBYDV-PAV incidence declined with high nitrogen supply, co-inoculation, or presence of soil microbes exposed to long-term low nitrogen enrichment. However, when combined, the negative effects of these treatments were sub-additive: nitrogen and co-inoculation did not reduce BYDV-PAV incidence in plants grown with the soil microbes. While soil microbes impacted leaf chlorophyll, they did not alter biomass or CYDV-RPV incidence. C_LIO_LISoil microbes mediated the effects of nitrogen supply and co-inoculation on infection incidence and the effects of infection on host symptoms. Thus, soil microbial communities can indirectly control disease dynamics, altering the effects of nitrogen enrichment on plant-pathogen and pathogen-pathogen interactions in terrestrial systems. C_LI