Common bunt of wheat

The causal agent of common bunt is the fungus Tilletia laevis (also known as Tilletia foetida). It is a major fungal pathogen affecting wheat, barley, and several wild grasses. The disease is characterized by the replacement of the grain endosperm with masses of fungal teliospores. These spores serve as the primary inoculum, persisting in the soil or adhering to the surface of seeds, ready to infect the next crop cycle.

Visible symptoms typically appear during the heading stage. Infected heads remain green longer than healthy ones and have a slightly different, more elongated appearance. The glumes often spread apart, revealing the bunted grains. When these grains are crushed, they emit a distinct fishy odor caused by trimethylamine, and a dark, powdery mass of spores is released instead of the healthy grain content.

Infection occurs during the germination stage, specifically when the seedling is transitioning from the grain to the first leaf. The fungus penetrates the young shoots when soil temperatures are cool, typically between +5°C and +15°C. Once the mycelium invades the growing point, it grows systemically within the plant, eventually reaching the developing ovary to produce the characteristic spore clusters.

The impact of common bunt is significant, leading to both quantitative and qualitative yield losses. Beyond the reduction in grain weight, the presence of teliospores disqualifies the harvested grain from commercial use due to the unpleasant odor and contamination risks. In severe cases, infestations can render entire fields unfit for milling, causing substantial economic losses for producers.

Effective management requires a multi-faceted approach centered on the use of certified, disease-free seed. Seed treatment with systemic fungicides is the most critical intervention to eliminate spores present on the seed coat. Additionally, good agricultural practices such as crop rotation and choosing appropriate planting times—avoiding conditions that favor long germination periods in cold soil—are essential to keep the disease pressure low.