Kernel smut of sorghum

Systematic position and pathogen type: Sphacelotheca sorghi is a member of the kingdom Fungi, phylum Basidiomycota, and class Ustilaginomycetes. It is a specialized biotrophic plant pathogen classified as a smut fungus, which is known for its destructive impact on various grain crops, particularly within the Sorghum genus.

Diseases and host crops: This fungus is the primary cause of kernel smut, also known as covered smut, in sorghum plants. It affects various types of sorghum, including grain, sweet, and broomcorn varieties. The pathogen replaces the developing grain kernels with masses of dark, powdery teliospores enclosed in a persistent membrane.

Biology and life cycle: The life cycle is primarily seed-borne, with teliospores clinging to the surface of the seeds. Upon planting, the spores germinate simultaneously with the host seed, and the fungal hyphae infect the young coleoptile. The pathogen then grows systemically within the plant, eventually colonizing the floral tissues where it produces a new generation of spores.

Environmental conditions and impact: The development of the disease is highly favored by soil temperatures ranging from 18°C to 25°C and moderate soil moisture levels during germination. The economic impact is significant, as the pathogen causes direct yield losses by transforming healthy grain into smut sori, reducing both the quantity and quality of the harvested produce.

Control and management measures: Effective management relies heavily on seed treatments with systemic fungicides. Additional cultural practices include the use of resistant hybrids, crop rotation to reduce inoculum in the soil, and planting in well-warmed soil to ensure rapid seedling establishment, which helps the host plant escape the most critical window of fungal infection.