Molecular comparisons amongst wheat bymovirus isolates from Asia, North America and Europe

To study the variation between wheat bymovirus isolates and to resolve uncertainties about the identity of the virus in some countries, leaves of infected plants were obtained from nine sites in China and from one each in Italy, Germany, USA and Canada. The German isolate was obtained from rye and the Canadian isolate was the type strain of wheat spindle streak mosaic virus (WSSMV). In RT-PCR, using primers designed from a partial sequence of a French isolate (tentatively described as WSSMV), genome fragments were obtained from the Italian and the French isolates but not from the Chinese ones. Conversely, products were consistently obtained from the Chinese isolates, but not from the Italian or French ones, when primers were designed from the sequence of a Japanese isolate of wheat yellow mosaic virus (WYMV). Nucleotide sequences were obtained from regions at or near the 3'-terminus of RNA1 of six Chinese isolates and the four from Europe and North America, usually including the coat protein. Nucleotide and amino acid sequence comparisons demonstrated that the European and North American isolates were extremely similar and were therefore WSSMV, while the Chinese isolates were close to the Japanese isolate and were thus WYMV.