Karnal bunt of wheat

Karnal bunt, also known as partial bunt, is a fungal disease caused by the pathogen Tilletia indica. As a serious quarantine pest, this disease is strictly regulated internationally to prevent its spread into new wheat-growing regions, as it poses a significant threat to global trade and domestic production.

The disease primarily affects bread wheat, durum wheat, and triticale. Infection occurs during the flowering stage, where the fungus enters the developing kernel. Unlike common bunt, Karnal bunt typically infects the grain partially, starting from the embryo end and replacing the starch with a mass of dark, teliospores.

A key diagnostic characteristic of this disease is the presence of a distinct "rotten fish" odor in infested grain, caused by the production of trimethylamine. In the field, affected heads appear slightly distorted, and the glumes are forced open by the mass of black spores that replace the kernel tissue, making the infection visible upon close inspection.

The development of the fungus is highly dependent on environmental conditions. It thrives during periods of high humidity and moderate temperatures (15-25°C) specifically during the anthesis stage. Because teliospores can persist in the soil for several years, managing the disease requires long-term strategic planning and strict field monitoring.

• Use of certified, disease-free seed stocks.
• Implementation of rigorous quarantine and phytosanitary inspections.
• Application of foliar fungicides during the booting to flowering stages.
• Crop rotation to reduce soil-borne inoculum pressure.
• Sterilization of harvesting equipment used in infested areas.

The economic impact of Karnal bunt is twofold: it reduces grain yield through kernel replacement and severely impacts grain quality. The foul odor and dark discoloration associated with the spores render the grain unmarketable for human consumption, often leading to total rejection of shipments and significant losses for farmers.