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A total of 1048 pasture grass plants representing four species was sampled from five different sites in Tasmania and tested for infection with viruses known to infect them in other temperate regions of the world. The species were cocksfoot (Dactylis glomerata), tall fescue (Festuca arundinacea), perennial ryegrass (Lolium perenne), phalaris (Phalaris aquafica) and timothy (Phleum pratense). The only viruses isolated from the plants sampled were two luteovirus types which were recovered by aphids and caused symptoms of barley yellow dwarf (BYD) in oat indicator plants. A total of 140 plants (13%) were infected. One plant was infected with a vector specific RPV type [transmitted only by oat aphids (Rhopalosiphum padi) and serologically like the New York type RPV isolate], 138 were infected with PAV types (vector non-specific and serologically like the New York type PAV isolate) and one plant apparently contained a mixed PAV/RPV infection. The PAV isolates varied considerably in the intensity of symptoms which they induced in oat indicator plants. Viruses were isolated only from tall fescue and perennial ryegrass plants in this survey. The initial recovery of BYD isolates with oat aphids and with blackberry-cereal aphids (Sitobion fragariae) from the pasture samples was often not a good indication of their serological specificities, particularly in young pastures. These data provide the first information on the vector specificities of viruses which cause BYD in Australia and on their serological identity. |
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