Pages 583-593

Today just Smuts caused by Ustilago spp. and Tilletia spp.

The smuts are in the order Ustilaginales and are historically very serious.

They are obligate pathogens: biotrophs. Can be grown in culture but not easily.

They replace reproductive parts of plants with spores and mycelium and while they do not often kill the host they can reduce yield to zero.

There are about six genera of economically important smuts. They are as follows:

Ustilago - smut of small and coarse grains: Wheat, barley, oats and corn.

Tilletia - covered smut of wheat; bunt of wheat.

Sphacelotheca - Sorghum smuts.

Urocystis - Onion smut.

Smuts produce only two types of spores: Teliospores and basidiospores.

They replace reproductive and sometime vegetative parts of plants with black spore masses which are either loose or covered to a greater or lesser extent with a membrane.

Loose and grain smuts: Ustilago spp.

These smuts are no longer very serious but historically were more serious than the rusts because smut destroys the grain itself.

Corn smut, and loose smuts of barley, wheat and oats.

These diseases are not easily discernable until the plant heads and it is too late to treat. Control can only be preventative.

Corn smut Disease cycle Figure 11-145

Corn smut can overseason as teliospores on soil but the other loose smuts overseason as mycelium in the embryo of living seeds

These fungi grow with the plant after germination and actually stimulate the plant to grow better through hormonal action. The smutted heads then release spores to infect healthy seed heads.

No basidiospores are produced per se. Instead the teliospores from a basidium which germinates to form primary mycelium which fuses and then can infect the ovary or embryo of the seed.


Loose smut of wheat life cycle Figure 11-147

Covered Smut or Bunt: Tilletia spp.

Also called stinking smut - This disease is actually two diseases caused by three species of Tilletia

Common Bunt: Tilletia caries; T. foetida

Dwarf Bunt: Tilletia contraversa

Common bunt is well controlled now in the developing world but Dwarf Bunt is still a problem in the Pacific Northwest.

Bunt causes stunting of plants and replaces the endosperm of grain with bunt balls.

Disease cycle : Figure 11-149

Bunt teliospores germinate to form 8-16 basidiospores (14-30 in T. contraversa).

These are usually called primary sporidia. These fuse by bridging to form dikaryotic mycelium which then produces secondary sporidia (dikaryotic) which then germinate to infect the seedling. Infection can be from the soil or form contaminated seeds.

Grows intercellularly and follows growing point of the plant. Grows into kernels and replaces the endosperm.

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