Structural diversity of Ym2, a gene conferring resistance against Wheat yellow mosaic virus

Allelic variation in Ym2 is available for breeding WYMV resistant bread wheat in China. Infection by Wheat yellow mosaic virus reduces both the yield and end-use quality of winter wheat. As the pathogen resides in the soil, the most effective disease control strategy is to breed varieties harboring a gene or genes conferring resistance. One such gene is Ym2, which has been introduced into bread wheat from its diploid wild relative Aegilops sharonensis. The gene has since been isolated and shown to encode a CC-NBS-LRR protein, but no concerted attempt has been made to date to characterize whether allelic variants of the gene are present in the bread wheat gene pool. In conjunction with previously published sequence data, the newly acquired data have enabled the identification of a total of 22 haplotypes at Ym2 locus, of which 14 are functional with respect to conferring resistance to WYMV; of these 14, 12 encode a non-synonymous amino acid variant(s), while two feature the insertion of a short nucleotide sequence into the coding region. While the functional haplotypes are all represented among the American and Japanese entries, none were harbored by Chinese germplasm, indicating that Ym2 has not been exploited to date by Chinese wheat breeders.