The disease ergot of rye produces sclerotia is caused by

The disease ergot of rye produces sclerotia caused by Claviceps purpurea.
Ergot (Claviceps purpurea) is a fungal parasite of cereals and grasses that produces toxic alkaloids.
The infection of wheat occurs at the flowering stage, and the fungus sclerotia, commonly called "ergot bodies," grows in place of the kernel. Ergot bodies are similar in size and shape to wheat kernels.