Common bunt, also known as stinking smut and covered smut is a disease of both spring and winter wheat

Wheat

Wheat is a cereal grain, originally from the Levant region of the Near East, but now cultivated worldwide. In 2007 world production of wheat was 607 million tons, making it the third most-produced cereal after maize and rice...

s. It is caused by two very closely related fungi, Tilletia tritici

Tilletia tritici

Tilletia tritici is the causal agent of common bunt of wheat.The tilletia was named after French agronomist Mathieu Tillet .-Use as a biological weapon:...

(syn. Tilletia caries

Tilletia caries

Tilletia caries is a plant pathogen that infects wheat causing the disease bunt. Plants infected with the disease are often slightly stunted, occasionally with yellow streaks on the flag leaf. Grain is replaced with bunt balls containing masses of black spores. At ripening, the ears take longer to...

) and T. laevis

Tilletia laevis

Tilletia laevis is a plant pathogen that causes bunt on wheat.It was used as a biological weapon by Iraq against Iran during the Iran-Iraq war in the 1980s.- External links :* *...

(syn. T. foetida).

Symptoms

Plants with common bunt may be moderately stunted but infected plants cannot be easily recognized until near maturity and even then it is seldom conspicuous. After initial infection, the entire kernel is converted into a sorus consisting of a dark brown to black mass of teliospores covered by a modified periderm, which is thin and papery. The sorus is light to dark brown and is called a bunt ball. The bunt balls resemble wheat kernels but tend to be more spherical. The bunted heads are slender, bluish-green and may stay greener longer than healthy heads. The bunt balls change to a dull gray-brown at maturity, at which they become conspicuous. The fragile covering of the bunt balls are ruptured at harvest, producing clouds of spores. The spores have a fishy odor. Intact sori can also be found among harvested grain.

Disease cycle

Millions of spores are released at harvest and contaminate healthy kernels or land on other plant parts or the soil. The spores persist on the contaminated kernels or in the soil. The disease is initiated when soil-borne, or in particular seed-borne, teliospores germinate in response to moisture and produce hyphae that infect germinating seeds by penetrating the coleoptile before plants emerge. Cool soil temperatures (5° to 10°C) favor infection. The intercellular hyphae become established in the apical meristem

Meristem

A meristem is the tissue in most plants consisting of undifferentiated cells , found in zones of the plant where growth can take place....

 and are maintained systemically within the plant. After initial infection, hyphae are sparse in plants. The fungus proliferates in the spikes when ovaries begin to form. Sporulation occurs in endosperm tissue until the entire kernel is converted into a sorus

Sorus

A sorus is a cluster of sporangia .In fungi and lichens, the sorus is surrounded by an external layer. In some red algae it may take the form of a depression into the thallus....

 consisting of a dark brown to black mass of teliospores covered by a modified periderm, which is thin and papery.

Pathotypes

Well-defined pathogenic races have been found among the bunt population, and the classic gene-for-gene relationship

Gene-for-gene relationship

The gene-for-gene relationship was discovered by Harold Henry Flor who was working with rust of flax . Flor was the first scientist to study the genetics of both the host and parasite and to integrate them into one genetic system...

is present between the fungus and host.

Management

Control of common bunt includes using clean seed, seed treatments chemicals and resistant cultivars. Historically, seed treatment with organomercury fungicides reduced common bunt to manageable levels. Systemic seed treatment fungicides include carboxin, difenoconazole, triadimenol and others and are highly effective. However,in Australia and Greece, strains of T. laevis have developed resistance to polychlorobenzene fungicides.