Differential aggressiveness of Bipolaris microstegii and B. drechsleri on Japanese stiltgrass.
Severe leaf blight of Japanese stiltgrass (JSG) from Bipolaris disease, causing significant decline in population density at some locations, has been reported sporadically in the field. Even so, much of the JSG in the mid-Atlantic is not diseased. Six populations of JSG from the field, one that was severely diseased by B. microstegii and the others "healthy", were tested by artificial inoculation for susceptibility to both B. microstegii (five isolates) and B. drechsleri (three isolates). Populations of JSG in this study differed in their response to the two Bipolaris species, but within species of Bipolaris the plant responses were consistent. Plants from the diseased population of JSG from Frederick, MD, were very susceptible to B. microstegii, and plants from other populations from Maryland (three locations), Delaware, and Indiana were not. In contrast, B. drechsleri caused moderate disease on plants from all accessions but one, and it was significantly less aggressive than was B. microstegii on the susceptible accession of JSG. Results of a limited host range determination only with B. microstegii revealed hypersensitive responses, and therefore high levels of resistance, in corn (four cultivars) and sorghum (three accessions). The native, sympatric grass deertongue was not diseased in these tests. Results reveal a distinct differential response among populations of JSG to disease from B. microstegii, while in contrast, B. drechsleri is capable of causing disease on a broader range of JSG populations.