Proso millet smut

The disease is caused by the basidiomycete fungus Ustilago crameri. It is a highly specific pathogen that primarily attacks proso millet (Panicum miliaceum). The fungus is classified as a smut disease, which is characterized by the replacement of healthy grain tissues with a mass of dark fungal spores.

The pathogen specifically infects millet crops. The primary route of infection occurs during the seedling stage. The fungus penetrates the young plant tissue from spores located on the seed coat or within the soil. Once inside, the mycelium spreads systemically throughout the host plant as it matures, remaining largely invisible until the plant begins to head.

Symptoms are typically visible during the panicle emergence phase. Affected panicles show signs of deformation, where individual grains are replaced by spore sori covered by a thin, greyish membrane. As the plant approaches maturity, these membranes rupture, releasing dark brown to black teliospores that spread easily by wind or during harvest equipment operations.

The spread and development of the disease are heavily influenced by environmental conditions during planting. Specifically, cool soil temperatures combined with moderate soil moisture that delays seedling emergence significantly increase the infection rate. Rapid germination and vigorous seedling growth are natural barriers that reduce the time the plant is vulnerable to Ustilago crameri.

The economic impact of this smut is significant, as every infected panicle results in a total loss of potential yield. To prevent and control the spread of the pathogen, producers should implement the following strategies:

• Treat seeds with effective fungicides before sowing to eliminate surface inoculum.
• Rotate crops to prevent the accumulation of fungal spores in the soil.
• Plant certified, healthy seed stocks free from smut contamination.
• Ensure soil temperatures are optimal for rapid and uniform crop germination.