Two of the five species of European blackberry (Rubus fruticosus L. aggregate) along the West Coast of the United States are considered invasive. They are also similar in appearance. Biological control of invasive blackberry by Phragmidium violaceum, causal agent of a rust disease, had been under consideration when rust-diseased blackberry was discovered in Oregon in 2005. An investigation was initiated to determine whether this disease would be an important factor affecting population density of these blackberries. Surveys were made over a 5-yr period at more than 30 field sites in the Willamette Valley and along the Pacific coast of Oregon. Diseased and nondiseased blackberry specimens were collected for artificial greenhouse inoculations and for identification. The two blackberry species, Rubus armeniacus and R. praecox, were identified as the most invasive. They were readily distinguished morphologically on the basis of inflorescence and flower characteristics and to a certain extent by differences in primocane leaf and leaflet shape. Artificial greenhouse inoculation studies revealed that R. praecox was susceptible to the rust disease and that R. armeniacus was not. These results were confirmed during a field survey. Results of this investigation revealed that the rust disease will not be effective for biological control of R. armeniacus and other approaches to management of this particular species will be required.
Severe leaf blight of Japanese stiltgrass (JSG) fromBipolarisdisease, 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 byB. microstegiiand the others “healthy,” were tested by artificial inoculation for susceptibility to bothB. microstegii(five isolates) andB. drechsleri(three isolates). Populations of JSG in this study differed in their response to the twoBipolarisspecies, but within species ofBipolaristhe plant responses were consistent. Plants from the diseased population of JSG from Frederick, MD, were very susceptible toB. microstegii, and plants from other populations from Maryland (three locations), Delaware, and Indiana were not. In contrast,B. drechslericaused moderate disease on plants from all accessions but one, and it was significantly less aggressive than wasB. microstegiion the susceptible accession of JSG. Results of a limited host range determination only withB. microstegiirevealed 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 fromB. microstegii, while in contrast,B. drechsleriis capable of causing disease on a broader range of JSG populations.
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