Rathayibacter rathayi

Rathayibacter rathayi is a phytopathogenic bacterium responsible for a disease known as yellow slime or bacterial head blight in various grasses. It is a significant concern for seed production, particularly for orchard grass and wheat, as it causes severe malformation of the inflorescences and destroys the reproductive capacity of the host plant.

The disease cycle is often linked to the interaction with nematodes of the genus Anguina. These nematodes act as vectors for the bacteria, carrying the pathogen to the developing host tissues. Once the nematodes create wounds in the plant, the bacteria infiltrate the site, leading to massive colonization and the production of a thick, yellow bacterial exudate.

The primary symptom of infection is the presence of a sticky yellow or orange slime on the floral parts, which eventually dries into a hard, crusty mass. Infected spikes exhibit extreme distortion, and seed formation is frequently stunted or completely aborted. These symptoms are easily recognizable during the heading stage of the grass lifecycle.

Environmental conditions such as high humidity and moderate temperatures during the flowering period are highly favorable for the spread of Rathayibacter rathayi. The pathogen can survive for several years in dried galls or on plant debris in the soil, which increases the difficulty of eradicating the disease once it is established in a field.

Effective management requires a multi-faceted approach. Key practices include:

• Sourcing certified disease-free seed lots.
• Implementing strict crop rotation programs to break the pathogen cycle.
• Deep plowing to bury infested residues.
• Control of nematode vectors to minimize pathogen transmission.
• Regular field scouting for early detection and quarantine measures.