Karnal bunt of wheat

Karnal bunt, caused by the fungus Neovossia indica (syn. Tilletia indica), is a destructive plant disease affecting wheat and triticale. As a regulated quarantine pest in many countries, it poses a significant threat to global grain trade and requires strict phytosanitary oversight to prevent its spread into new regions.

The pathogen primarily attacks the wheat kernel, replacing the starch with masses of black teliospores. Often, only a portion of the grain is affected, but the presence of the fungus produces a distinct, unpleasant "fishy" odor caused by trimethylamine, which contaminates entire batches of grain and renders them unfit for consumption or milling.

The disease cycle begins with the germination of teliospores that have overwintered in the soil or were introduced via contaminated seeds. Under conditions of high humidity and moderate temperatures, the fungus produces sporidia, which are wind-borne to the flowering spikes. Once the spores penetrate the florets, the mycelium colonizes the developing seed.

Environmental factors are crucial for the development of Karnal bunt. The infection process is most successful when rain or high humidity levels occur during the anthesis (flowering) stage of the wheat crop. Unlike other bunt diseases, Neovossia indica does not infect the seedling, but specifically targets the reproductive organs at a precise phenological stage.

Economic damage includes yield reduction and strict trade embargoes on grain produced in infested areas. Management strategies focus on prevention and containment, including:

• Utilizing pathogen-free certified seeds.
• Implementing long-term crop rotations to reduce soil-borne inoculum.
• Proactive surveillance and laboratory testing of crops in high-risk zones.
• Application of targeted fungicides during the heading stage when environmental forecasts predict wet weather.