Some smut diseases

A. Loose smut of oats (Avena sativa) caused by Ustilago nigra.
B. Covered smut of oats (Avena sativa) caused by Ustilago hordei.
C. Black loose smut of barley (Hordeum vulgare) caused by Ustilago nigra.

Covered smut of barley (Hordeum vulgare) caused by Ustilago hordei:
D. Diseased spike with all kernels replaced with masses of teliospores and healthy spike.
E. Some barley varieties will start showing pustules containing teliospores on the flag leaf before heading.

Covered smut of barley (Hordeum vulgare) caused by Ustilago hordei:
F. Close-up of a diseased spike with all kernels replaced with masses of teliospores. Note virtual absence of awns. 
G. Close-up of a partially diseased spike with some kernels replaced with masses of teliospores and others having "pockets" of spores. Note fairly intact, but deformed and sometimes smutted awns. 
H. Close-up of a diseased spike with all kernels replaced with masses of teliospores. Smut fungi have been long known for their ability to perturb (or reset?) plant differentiation processes. Although not commonly known for Ustilago hordei, some subtle changes can sometimes be seen such as the induction of a complete inflorescence in place of a single kernel, shown here.