Identification and classification of a resistance breaking strain of barley yellow mosaic virus

Summary A “resistance breaking” isolate of barley yellow mosaic virus-2 (BaYMV-2) was cloned as a cDNA and characterised. Restriction mapping and comparison with a German and a Japanese isolate of BaYMV (BaYMV-G and BaYMV-J) revealed a high level of restriction site conservation for RNAl and the majority of RNA2. However, in a box of approximately 600 nucleotides located on RNA2, striking differences in the restriction pattern could be identified. The nucleotide sequence of this box, as well as of the 3‘-terminal region of RNA1 including the coat protein coding region, and the deduced amino acid sequences were analysed. Identity at the amino acid level was between 99.3% and 92.3% in comparison with the corresponding sequences of BaYMV-G and BaYMV-J, suggesting that BaYMV-2 is closely related to BaYMV. Consequently, the classification of BaYMV-2 as a “resistance breaking” strain of BaYMV is justified.