Variation in pathogenicity and host range of bipolaris sp. causing leaf blight disease on the invasive grass microstegium vimineum

Microstegium vimineum is a widespread invasive grass that poses significant threats to forests and disturbed areas throughout the United States. Often, the large-scale, rapid spread of Microstegium prohibits management by traditional methods. Control of Microstegium may be possible through the use of a pathogen (referred to here as Bipolaris Mv) that causes leaf blight on Microstegium. Members of the fungal genus Bipolaris are known pathogens of many plants, including important agronomic crops. However, little is known about the biology and host range of Bipolaris Mv. We used a series of growth chamber and light bank experiments to determine the variation in Bipolaris Mv from different geographic origins and its ability to cause foliar lesions and chlorosis on Microstegium. We used petri plate and soil infestation assays to determine the effects of Bipolaris Mv on Microstegium emergence from seed, biomass, and root necrosis. Finally, we tested the host range of these fungi on economically and ecologically important plant species. All isolates increased disease on Microstegium foliage relative to controls, although the effects varied among isolates. Isolates increased root necrosis by 97% in petri plate assays and by 4% in soil infestation trials compared to controls. Infestation of soils with Bipolaris Mv reduced emergence of Microstegium from seed by 31% compared to controls, but did not affect root or stand biomass. Bipolaris Mv produced lesions on a range of grasses, including corn, sorghum, rye, and wheat, although lesion size varied with isolate. These results indicate that Bipolaris Mv may be an effective pathogen on Microstegium, but its use as a bioherbicide may be impractical because of its effects on a wide range of grasses.