COS 282-3 - Consequences of crop pathogen spillover and fire for native grass hosts

Abstract: Grasslands are one of the most threatened ecosystems globally and are a high priority for conservation. The primary drivers of decline are agriculture and fire suppression. One potential but understudied threat to grasslands is the spillover of crop pathogens from agricultural landscapes into native hosts. The barley and cereal yellow dwarf viruses (YDV) are economically damaging crop pathogens vectored by aphids. Our previous work showed that YDVs are widespread in big bluestem (Andropogon gerardi), Indiangrass (Sorghastrum nutans), and little bluestem (Schizachyrium scoparium) populations in restored and remnant grasslands in New York. We also found that grasslands managed with fire were correlated with lower overall pathogen prevalence. We then conducted a multi-year common garden experiment using grass seeds from previously studied grasslands. Our goal was to determine host susceptibility and response to YDV and the interaction with fire. We used a multifactorial blocked design with 13 plant communities crossed with a burn treatment. Plants were tracked throughout the experiment for YDV infection, growth, and reproduction. Two-way ANOVA were used to examine YDV prevalence, the effect of burning, and the effect of pathogen infection on plant response traits. Here we report results from Year 2, following one experimental burn.

We found YDV infection in A. gerardi, S. nutans, and S. scoparium in the first year post-planting. As with our previous survey, A. gerardi had the highest virus prevalence. We also found that burn treatment was associated with significant reduction in infection in A. gerardi, whereas S. nutans and S. scoparium were similar between burn treatments. We found that YDV infection significantly reduced plant height in A. gerardi regardless of burn treatment, similar to effects of infection in crop hosts. We also found that burned S. scoparium had higher seed weight, and S. nutans had higher reproductive shoot counts than unburned plants regardless of YDV infection status. Our study indicates that spillover of YDV occurs from surrounding land use types into native grass communities. The higher virus prevalence in A. gerardi suggests that this dominant grassland competitor has high susceptibility to YDV. The finding that A. gerardi exhibits growth reduction when infected with YDV means further study of community level effects is needed. However, since burning seems to reduce pathogen prevalence in this host, management with fire may attenuate some negative effects. For S. nutans and S. scoparium, burning may directly mitigate the potential fitness cost of YDV infection through improved reproductive output.