Wheat soil-borne mosaic

Wheat soil-borne mosaic (WSBM) is a viral disease caused by the Wheat soil-borne mosaic virus (WSBMV). The virus is transmitted by the soil-borne plasmodiophorid Polymyxa graminis. This vector acts as a reservoir, housing the virus within its resting spores, which can remain infective in the soil for a decade or longer, making the pathogen extremely persistent.

The disease primarily targets winter cereals, specifically winter wheat and winter barley. Infections are typically localized, appearing in patches within fields, particularly in low-lying, poorly drained areas where moisture levels facilitate the movement and colonization of Polymyxa graminis zoospores in the root system.

Symptoms become visible in the early spring as the crop resumes growth. Typical signs include chlorotic mottling, mosaic patterns, and streaking on the leaves. Infected plants often exhibit stunted growth, reduced tillering, and sometimes tissue necrosis. In severe cases, the affected area of the field may show significant thinning and yield loss.

Environmental conditions play a crucial role in disease development. Cool and wet soil conditions during the autumn, followed by a cool spring, favor the infection process. The virus spreads spatially through the movement of soil containing infected cysts, which can be easily transported by farm machinery, tools, or water runoff during heavy rainfall events.

Yield impact can be substantial, with losses ranging from minor to over 50% depending on the cultivar's susceptibility. Management strategies are focused on long-term prevention rather than chemical intervention. Key tactics include the selection of resistant wheat and barley cultivars, extending crop rotation cycles to starve the fungal vector, and improving soil drainage to minimize the conditions suitable for the spread of Polymyxa graminis.