Identification of Barley mild mosaic virus Isolates in Germany Breaking rym5 Resistance*

In winter and early spring 2004 unequivocal mosaic symptoms were detected for the first time in Germany on six plants of the barley cv. Tokyo carrying the resistance gene rym5. By serological and electron microscopic investigations Barley mild mosaic virus (BaMMV) was identified in all plants and could be re-transmitted to cv. Tokyo as well as to additional cultivars carrying rym5. In contrast to this, genotypes carrying the resistance genes rym1 + rym5, Rym2, rym4, rym7, rym9, rym11, rym12, rym13, Rym14Hb, rym15 or Rym16Hb turned out to be resistant. Furthermore, the BaMMV isolates were not transmissible to different dicotyledonous species. Sequence analyses in the VPg coding region of RNA1 revealed differences to the known sequence of the original BaMMV isolate (BaMMV-ASL1, AJ 242725) and also of a French pathotype (BaMMV-Sil, AJ 544267, AJ 544268) which is also able to overcome the resistance mediated by rym5. At least in one location a spread of the area infested by this new strain was observed in 2004 ⁄ 2005 and 2005 ⁄ 2006