Grain smut of sorghum is externally seed borne disease caused by pathogen

Grain smut of sorghum is an externally seed-borne disease caused by the pathogen Sphacelotheca sorghi.
The pathogen is externally seed borne. Optimum environmental conditions for maximum infection include: temperatures between 20° and 25°C and slightly acidic soils favour the disease development.
The affected plants can be detected before the ears come out. They are shorter than healthy plants with thinner stalks and marked tillering. The sorus is covered by a thin membrane that ruptures very early, exposing the spores even as the head emerges from the sheath.