Viruses of Gramineae in Germany - a short overview

In Germany, more than 30 different viruses infecting plants of grasses and cereals have been identified. :Mainly wild grasses or grasses in pastures a re hosts of these viruses and also sources from which at least some of them can he transmitted to cereals. Some of these viruses, viz., Lolium latent virus, Molinia streak virus, Barley mild mosaic virus, and Soil-borne cerea l mosaic virus (soil-borne cereal mosaic Virus is proposed as a new name), were newly described from Germany. The economical importance of the :viruse s predominantly infecting grasses is difficult to assess. On cereals, only few of the gramineae viruses cause serious damage. First of all, the soil-b orne barley infecting Barley yellow mosaic and Barley mild mosaic viruses a re important pathogens although their impact could be drastically reduced a fter successful breeding of resistant (immun) cultivars. From the few regio ns where they were first detected in 1978, these two viruses were rapidly s pread and occur today in most barley-growing regions of Germany. Basing on the average survival rate of their vector Polymyxa graminis is assessed tha t soil contaminated by these viruses remains infested for up to 50 years. S ince 1990, in Germany the spread of Wheat spindle streak mosaic and Soil-bo rne cereal mosaic viruses is observed which, however, predominantly infect plants of rye and triticale. The importance of Barley yellow dwarf virus (B YDV) is much lower in Germany than generally assumed. In average, less than 1 % of cereal plants become infected during young stages of development le ading to yield losses. Only in western parts of Germany with comparably mil der climatic conditions, cereals may be more seriouly endangered to become infected hv BYDV than in other regions. Sporadically, local epidemics of BY DV were favoured in other regions by unusual environmental conditions. Alth ough detected in Germany for the first time in 1990, the occurrence of Whea t dwarf virus pathogen of cereals is not yet realized enough. This virus is economically much more important than BYDV. Wheat dwarf virus causes simil ar symptoms as BYDV. therefore, the visual diagnosis of both diseases requi res some experiences.