Wheat spike blight

Pathogen and disease type
Wheat spike blight is a bacterial disease caused by Rathayibacter tritici. It is a unique phytopathological case because the bacterium cannot invade plant tissues independently. It requires the wheat seed gall nematode Anguina tritici to act as a vector. The nematode carries the bacteria into the wheat plant, leading to systemic infection.

Susceptible crops
The primary host for this complex disease is wheat. Winter wheat is particularly susceptible, as its long developmental cycle in the soil coincides with the activity period of the nematode vectors. Although some wild grasses may harbor the pathogen, economic losses are almost exclusively associated with commercial wheat cultivation.

Symptoms and signs
The disease manifests during the heading stage. Infected plants exhibit stunted growth, leaf twisting, and yellowing. The most diagnostic sign is the presence of a yellow, bacterial slime (gummosis) on the heads, which eventually dries and glues the glumes together. Instead of healthy grains, the plant produces distorted galls filled with bacterial mass and nematode larvae.

Conditions for development and spread
The development of the blight is highly dependent on environmental conditions, specifically moisture. High humidity during the tillering and jointing stages of wheat favors the emergence and movement of nematodes from the galls to the growing points of the wheat plants. The primary means of long-distance spread is through contaminated seed lots containing galls.

Damage and control measures
The disease causes significant reductions in grain yield and can lead to complete sterility of the infected spikes. Effective control focuses on preventing the introduction of the pathogen. Strategies include using certified, nematode-free seeds, employing physical seed cleaning methods (such as salt flotation or gravity separation), and implementing crop rotation cycles to starve the nematode population in the field.