Plant pathogens and mutualists can play an important role in plant performance. While previous studies indicated that the interaction between mycorrhizal fungi and plant enemies cause changes in overall plant performance, there have been no experimental studies explicitly studying the interactions between mutualistic mycorrhizal fungi and viral pathogens. Here we investigate the impact of arbuscular mycorrhizal fungi (AMF) and Barley Yellow Dwarf Virus (BYDV) on plant performance. While AMF provide a nutritional benefit to the host plant in the form of nitrogen and phosphorous, BYDV infection is systemic and localized to the phloem, where it causes necrosis and disruption of carbohydrate translocation.Using the invasive species Avena fatua (wild oats) we factorially manipulated AMF presence and BYDV infection in a greenhouse experiment using 72 plants. Plants were conditioned with a mixture of naturally occurring mycorrhizae. For plants which were conditioned with AMF, this mixture was mixed with a sterilized sandy loam soil while plants without AMF received a sterilized version of the natural inoculum. For pathogen infection, plants were infected via aphid vector (Rhopalosiphum padi) with an isolate of the PAV strain of BYDV. In order to control for herbivory effects, uninfected aphids fed on uninfected plants and infected aphids fed on infected plants. To assess plant performance, we measured germination rate, survivorship, above and belowground biomass, tiller number, BYDV infection, aphid reproduction, AMF colonization, seed production, photosynthetic capacity and longest leaf length.  

Results/Conclusions

Two weeks after infection, infected plants had significantly higher aphid reproduction then uninfected plants. Plants infected with BYDV also had significantly shorter leaf lengths then compared to uninfected plants. Neither leaf length nor aphid reproduction was impacted by AMF colonization and BYDV infection. Tiller number was not significantly impacted by any of the treatments. Thus, BYDV infection decreased plant performance while AMF colonization did not have any impact on plant performance. This study explored the strength and nature of multiple, co-occurring interactions between viruses and mycorrhizal fungi and their overall impact on plant performance.