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Wheat crops from all major wheat-growing districts throughout Victoria were sampled during September 1984. Examination of pooled samples by enzyme-linked immunosorbent assay (ELISA) with an antiserum to a mixture of two barley yellow dwarf virus (BYDV) types ('V1') showed that 10 out of 26 crops were infected with BYDV and 3 out of 26 had a BYDV incidence greater than 10%. The overall loss in yield likely to result from BYDV was estimated at 2% with a far greater loss in some crops. Frozen-stored samples from four crops with high levels of BYDV were retested after one year with isolate-specific antisera. The results indicated that in these crops, PAV-related isolates were the most common, followed by RPV-related isolates.

Plants with symptoms of barley yellow dwarf virus (BYDV) obtained in infection feeding assays of aphids collected in the field in Idaho between 1986 and 1988 were tested for virus transmissibility by possible aphid vectors. Isolates obtained during 1987-1988 were also tested with a range of polyclonal antisera which distinguished PAV, MAV, SGV, RPV and RMV serotypes. In 1989 some Idaho (ID) BYDV isolates, maintained as standards for comparison, were serotyped and tested for aphid transmissibility, using 11 species of aphids.There was not always the expected correspondence between serotype and vector specificity for ID isolates. For isolates obtained from field-collected Rhopalosiphum padi, vector transmissibility and serotype corresponded with previous reports; however, 44% of isolates which were serotyped as RMV were also transmissible by species other than Rhopalosiphum maidis. Similarly, the transmissibility of the ID laboratory standards did not always conform to the reported vector specificity of serotypes. The laboratory ID-MAV culture was transmitted by Metopolophium dirhodum and Myzus persicae as well as by Sitobion auenae. The laboratory ID-SGV culture was transmitted by R. padi and S. auenae as well as by Schizaphis graminum. The ID-RPV culture was transmitted by S. graminum and Rhopalosiphum inserturn as well as R. padi. Both of two laboratory ID-RMV cultures were transmissible by R. inserturn and R. padi transmitted one of them. The results indicate that, for isolates collected in Idaho, vector specificity cannot be assumed from their serotypes.

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Four serologically distinct types of barley yellow dwarf virus (BYDV) were identified infecting cereals and grasses collected around mainland Australia. On the basis of serological relatedness to North American type-isolateq, the Australian isolates were classified as MAV-, PAV-, RMV- and RPV-like. However, aphid transmission studies showed that, while the Australian PAV-, RPV-, and RMV-like isolates had conventional vector relationships, the Australian MAV-like isolates had Rhopaloszphium padi as a major vector species. Differences in the Sitobion species occurring in North America and Australia made comparisons of the transmissibility of MAV- and PAV-like isolates by these vectors impractical. Isolates serologically like PAV were by far the most common viruses in each State surveyed, with the next most common varying from State to State. The identifications of RMV- and MAV-like isolates are the first confirmed records of these types of BYDV in Australia.

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