Characteristics and drivers of plant virus community spatial patterns in US west coast grasslands

The spatial distribution of disease risk caused by multi-pathogen infections is not frequently characterized, limiting understanding of the drivers of infection and thwarting prediction of future risk in a changing environment. Further complicating this predictive understanding is that interactions among multiple pathogens within a host commonly alter transmission success, infection risk, and disease dynamics. By characterizing spatial patterns of Barley and Cereal Yellow Dwarf Virus (B/CYDV) infections that range from the scale of an individual plant to thousands of neighboring plants, we examined the contributions of spatial processes to the distribution of disease risk. In a two-year field experiment, we planted grass hosts of B/CYDVs into fertilized plots of US west coast grasslands. We determined how vector-sharing, environmental conditions and spatial variation in host quality affected spatial patterns of single viruses, pairs of viruses and the whole virus community across out-planted grass hosts. We found that single viruses and virus communities were spatially random, indicating that infection does not solely spread through the community in a wave-like manner. On the other hand, we found that pairs of viruses, especially those that share a vector species, were aggregated spatially. This suggests that if within-host competition exists, it is not strong. Aggregation in one pair of viruses was more frequent due to environmental conditions and spatial variation in out-planted host quality, measured as vector preference. These results highlight the importance of insect vectors for predicting the spatial distribution of coinfection risk by B/CYDVs.