Damage: Mosaic symptoms are sometimes accompanied by necrotic spots and yellow patches, and old leaves die rapidly. Symptoms appear on leaves in early spring, but symptoms gradually disappear as the weather warms. When the temperature is above 20°C, new leaves will not show symptoms. When the temperature is between 5 and 10°C, the growth of infected plants is restricted, especially in soil with high humidity. When this weather continues into April, infected plants become dwarfed. Although dwarfed plants respond to rising temperatures in spring, yields are still reduced by 80% (Hillamp; Evans, 1980; Huth, 1988a).
Method of transmission: The virus can be transmitted mechanically.
Virus vector: spread by Polymyxa graminearum. The virus is spread by dormant spores or zoospores released from zoosporangia in the roots of barley.
Natural host: Hordeum vulgare.
Plants that can be infected by artificial inoculation: The host range of the virus is very narrow, mainly concentrated on grass plants, mainly barley, goat grass (Aegilops spp.), upland wheat grass Eremopyrum triticeum, rabbit tail The grasses Lagurus ovatus, Triticosecale, Secale cereale and durum Triticum durum, but not Triticum aestivum and Avena sativa, are not infected.
Disease, environment and prevalence: Barley mild mosaic virus and barley yellow mosaic virus have the same natural hosts and vectors, and often persist on naturally infected plants. They may be similar in disease epidemiology. In nature, they only infect autumn-sown barley and occur mainly in winter wheat growing areas. However, the possibility exists that spring wheat is a natural host of this virus (Adams et al. 1986). In diseased soil, dormant spores are spread as agricultural machinery turns the soil, often as evidenced by the expansion of infected, yellowing fields of barley. Such small plots gradually expand over the next few years until the entire field turns yellow. Agricultural machinery can spread viruses to adjacent fields, and diseased soil and sewage soil carried by the wind can spread viruses over long distances (Huth, 1991).
Disease control: The disease can be controlled only through agricultural operations. Varieties with the ym4 gene have certain resistance to virus replication and the spores released from the roots are non-toxic (Adams et al., 1987a).