Click on any
image for a more
detailed view

Significance

Historical Significance

Stinking smut is a disease that was recognized early in agricultural development because of its prominent symptoms and signs, e.g., black smelly masses of spores in the heads of wheat. As such, it caught the attention of early botanists and agriculturists. M. Tillet, a French biologist became intrigued with the black spore masses in 1755 and actually experimented with them to determine if they could cause the disease. Even though this was prior to the time when the "germ theory of disease" was accepted, he did show that the spores were associated with the disease. However, he believed that it was a "poisonous entity" associated with the black spore masses that actually caused the disease, not the fungus itself. It wasn't until nearly 100 years later that Anton deBary, the Father of Plant Pathology, confirmed the parasitic nature of the smut fungus.

From the late 1800s until the 1930s, stinking smut was a devastating disease of wheat, particularly in winter wheat grown in the Pacific Northwest. Infection levels over 20% were common in Washington in the early 1900s, and between 25-50% of the Kansas wheat crop was lost to stinking smut in 1890. Because of the dusty spore masses released during harvest, many "thresher" explosions occurred. Static electricity that developed around the combine machinery ignited the teliospore dust released by the combine. In 1915, 160 such explosions were reported in Washington. One can visualize the panic that must have developed when a "thresher-combine" pulled by a 20-40 horse team caught fire in the middle of a wheat field from such a smut dust-induced explosion! (Figure 10).

Figure 10

Only when the organic mercury and HCB seed treatments became available after 1930 did losses from smut drop to much lower levels. Today, losses from smut rarely occur unless a grower chooses not to plant treated seed.

OTHER BUNTS

Two other bunts of wheat are currently of interest and importance. One is dwarf bunt, also called TCK based on the name of the pathogen and its authority, Tilletia controversa Kühn. This is a disease exclusively of winter wheat since the teliospores only germinate when the soil temperature hovers around freezing for long periods of time, usually 90 days or longer. This condition is usually found under snow cover so dwarf bunt is restricted to areas where winter wheat is grown and that have long periods of snow. Currently, this disease is of economic importance from the standpoint that certain countries have an embargo on the importation of wheat carrying dwarf bunt teliospores. For some time, the United States was not able to sell wheat to China because we could not guarantee to the Chinese that U.S. wheat would carry absolutely no dwarf bunt spores. In 2000, China relaxed its embargo and now accepts wheat shipments with low levels of dwarf bunt teliospores.

Another bunt of economic importance because of its impact on trade is karnal bunt, caused by Tilletia indica. This fungus has a similar biology to that of the other smuts. However its disease cycle is somewhat different in that sporidia are blown up to open flowers, germinate on the stigma, and invade the developing seed. This smut was originally discovered in Karnal, India in the 1930s, but recently was found in Mexico, and now in a few wheat fields in the southwestern portion of the United States, particularly Arizona and neighboring areas of California. Many countries of the world restrict importation of wheat carrying teliospores of karnal bunt. Although the disease causes little yield loss, its greatest impact is because of its effect on wheat trade

RETURN TO TOP