Downy mildew

Downy mildew caused by Peronosclerospora is a major plant disease characterized by severe systemic infections in cereal crops. As an oomycete pathogen, it spreads rapidly under favorable environmental conditions, causing significant physiological disruption in host plants. It is recognized globally as a limiting factor for maize and sorghum production in tropical and subtropical regions.

The host range primarily includes maize (corn), sorghum, and sugarcane. The pathogen, specifically species like Peronosclerospora sorghi, invades the plant at the seedling stage through soil-borne oospores or airborne conidia. Once inside, the fungus colonizes the vascular tissues, spreading systemically throughout the developing plant organs.

Diagnostic symptoms are highly distinct: initial chlorotic streaks on leaves, followed by stunted growth and internode shortening. Under high humidity, a dense, whitish fungal growth consisting of sporangiophores and conidia emerges on the underside of the leaves. In severely affected maize, tassels may become sterile or malformed, failing to produce viable grain.

Environmental conditions drive the epidemic potential of this disease. Temperatures between 20°C and 25°C combined with high relative humidity or heavy dew are ideal for sporulation and infection. The pathogen can survive for extended periods as oospores within soil debris, allowing the disease to recur in fields if crop rotation and hygiene practices are not strictly managed.

Effective management strategies require an integrated pest management approach. This includes the use of disease-resistant hybrids, which remains the most reliable control method. Additionally, seed treatments with systemic fungicides are essential to protect germinating seeds from soil-borne infection. Crop rotation and the elimination of volunteer host plants are also critical components to reduce the primary inoculum load in the field.