Tall fescue is a potential spillover reservoir host for Alternaria species

The spread of invasive species is complicated and multifaceted. Enemy spillover (i.e. the transfer of a natural enemy from a reservoir host to a novel host) is one mechanism that facilitates the spread of non-native species. The reservoir host is a species that harbors high abundance of the enemy with little cost to fitness. We asked whether Schedonorus arundinaceus (tall fescue), a highly invasive grass species in North America, is a potential reservoir host for the ubiquitous genus of fungi, Alternaria. We also asked whether spillover of Alternaria is possible among grasses that commonly occur with S. arundinaceus in grassland ecosystems. We performed a greenhouse cross inoculation of three isolates of Alternaria and six grass species (three native, three invasive, including S. arundinaceus). We determined that spillover is possible because the fungal isolates infected and caused disease symptoms on all six grasses and decreased biomass in two of the grass species. We also determined that the invasive grass species appear to be more competent hosts than the native species and that S. arundinaceus could be a likely reservoir host for Alternaria spp. because it can harbor the pathogen with no apparent fitness cost.