Characterization of fungally and mechanically transmitted isolates of barley mild mosaic virus: two strains in competition.

The virus populations of two French barley mild mosaic virus isolates have been characterized using Western blot, sequence, PCR, and RFLP analyses. One of the isolates (M) was obtained by mechanical transmission of the other, fungally transmitted isolate (P). The results obtained show that the two isolates contain distinct RNA1 and RNA2 molecules with respect to their nucleotide sequences, and hence contain distinct barley mild mosaic virus strains. One strain is present mainly in isolate P and closely resembles a Japanese and two German isolates. It contains an RNA2 of approximately 3.5 kb. The other strain is present mainly in isolate M and closely resembles a UK isolate. This strain contains a smaller RNA2 of approximately 2.4 kb. The results show that mechanical transmission causes a shift in the virus populations in favor of the mutant strain.