Loose smut of sorghum

Taxonomic position and pathogen nature: Sporisorium cruentum is a basidiomycetous fungus belonging to the order Ustilaginales. It is a specialized biotrophic pathogen that exclusively infects members of the genus Sorghum, including forage crops like sudangrass, causing systemic infection within the host plant tissues.

Diseases and host plants: The fungus causes a disease known as loose smut of sorghum. The most distinct symptom is the replacement of the floral structures with a mass of teliospores. Unlike other smut types, this infection often causes the host's panicle to appear deformed and elongated, leading to the total destruction of the grain-bearing organs.

Biology and life cycle: The life cycle begins when teliospores contaminate the soil or the seed surface. Germination occurs simultaneously with seed germination. The pathogen enters the seedling at the coleoptile stage and grows systemically along with the apical meristem, remaining asymptomatic throughout the vegetative growth phase until the reproductive stage.

Developmental conditions and impact: Disease development is favored by moderate soil moisture and temperatures between 20°C and 30°C during the germination period. The damage is severe as infected plants become completely sterile. This leads to significant yield losses, reduced plant height, and poor nutritional quality of the forage if the plants are used for silage.

Protection and management measures: Controlling loose smut requires a combination of preventative measures and chemical interventions. Strategic management includes:

• Seed treatment with systemic fungicides to eliminate surface-borne inoculum.
• Crop rotation to reduce the concentration of teliospores in the soil.
• Use of certified pathogen-free seeds from reliable sources.
• Planting resistant or tolerant sorghum hybrids.