Polymyxa graminis

Polymyxa graminis is a soil-borne obligate parasite belonging to the Plasmodiophoridae family. In agriculture, it is recognized not only for its parasitic activity on cereal roots but primarily as the essential vector for transmitting economically damaging viruses, including the Wheat streak mosaic virus and Barley yellow mosaic virus.

The host range of this organism includes major cereal crops such as wheat, barley, rye, and oats. The pathogen invades the root epidermal cells, where it completes its life cycle by forming zoosporangia and resting spores. These spores can remain viable in the soil for over a decade, posing a long-term threat to agricultural fields.

Direct damage to roots by Polymyxa graminis is typically minor, but the indirect damage caused by the viruses it transmits is significant. Infected plants often exhibit stunted growth, chlorosis, yellow mosaic patterns, and systemic streaks on the foliage. This leads to reduced tillering, lower grain weight, and severe yield loss in susceptible varieties.

The development and spread of Polymyxa graminis are highly dependent on soil moisture and temperature. The parasite's zoospores are motile in water films, meaning that saturated or poorly drained soil provides optimal conditions for the infection cycle. Early autumn sowing often increases the risk of infection as soil conditions align with the pathogen's requirements.

Management practices are focused on reducing the inoculum density and preventing infection, as there are no chemical soil treatments available to eradicate this pathogen:

• Cultivation of resistant or tolerant crop varieties;
• Long-term crop rotation to reduce the pathogen population in the soil;
• Improved field drainage to prevent waterlogging;
• Strict control of volunteer cereals and grassy weeds that serve as alternate hosts.