Coniothyrium leaf spot of sorghum

Coniothyrium leaf spot, caused by the fungus Coniothyrium sorghi (synonym Phoma sorghina), is a common fungal disease affecting sorghum crops worldwide. It is primarily identified by its characteristic necrotic lesions that manifest on the foliage during the growing season.

The host range of this pathogen is strictly limited to species of the genus Sorghum. The disease is prevalent in humid regions where sorghum is cultivated, posing a threat to both grain and sweet sorghum varieties by compromising the photosynthetic capacity of the plants.

Symptoms typically appear as small, circular, or irregular spots on the leaf surface. These lesions are often light brown or tan with a distinct dark margin. In advanced stages of infection, small, black, dot-like fruiting bodies called pycnidia develop within the lesions, releasing spores that continue the cycle of infection.

Favorable conditions for the spread of this disease include warm temperatures and periods of high humidity or frequent rainfall. The pathogen survives the off-season primarily in infected crop debris left on the field, which serves as the primary inoculum source for the next generation of sorghum.

The economic impact of the disease is significant in cases of severe infestation, leading to premature leaf senescence and defoliation. This reduction in the active leaf area directly limits the plant's ability to fill grain or accumulate sugar, resulting in reduced yields and overall poor crop quality.

Effective management strategies include the implementation of cultural practices such as crop rotation and the thorough removal or deep burial of harvest residues to break the life cycle of the pathogen. Farmers are also advised to use certified, disease-free seed and apply foliar fungicides when environmental conditions favor disease development.