Spatial dynamics of a generalist plant pathogen in a fragmented landscape: Barley yellow dwarf virus in Cascade meadow systems

Background/Question/Methods

The spread of infectious disease epidemics and spatial patterns of disease incidence are influenced by the spatial structure of host communities. Spatial dynamics are particularly important for plant pathogens because natural plant communities exist in spatially heterogeneous landscapes, and host species are often distributed in patches that will influence how pathogens spread and persist. We investigated the role of local community interactions and the effects of landscape structure and regional processes on the dynamics of barley yellow dwarf virus (BYDV), an aphid-vectored generalist plant pathogen that infects numerous grass species. We measured the local and regional abiotic conditions, local host community composition, local vector abundances, and landscape metrics such as patch size and connectivity in four separate meadow systems in the Cascade Mountains in Oregon. At each site we also measured the prevalence of BYDV in Elymus glaucus and either Bromus carinatus or Bromus vulgaris to identify which variables were most strongly associated with local and regional pathogen prevalence. In addition to sampling meadows, we also collected data on hosts, aphids, and pathogen prevalence in the forest understory and along roads to determine whether roads serve as corridors for aphid dispersal and BYDV transmission.

Results/Conclusions

BYDV prevalence was significantly higher in B. carinatus than in B. vulgaris or E. glaucus. BYDV prevalence was also significantly higher in meadows compared with the forest and road sites. There was no effect of grass species richness or total grass abundance on BYDV prevalence at the site level, but site-level prevalence and the proportion of infected E. glaucus were both positively related to the abundance of B. carinatus. Meadow size was negatively correlated with total plant species richness but positively correlated with B. carinatus abundance, indicating that meadow size may positively affect BYDV prevalence through area impacts on host community composition. Total plant species richness was lower along roads than in meadow or forest sites, but grass species richness and abundance were higher along roads than in the forest. In addition, aphid abundance was higher along roads and in meadows than in forest sites, suggesting that roads through the forested landscape may serve as corridors for aphid dispersal and potentially BYDV transmission. Our results suggest that landscape structure and environmental conditions shape spatial patterns of BYDV incidence via their influence on local plant community composition.