Southern blight

Systematic position and pathogen type: Athelia rolfsii (formerly known as Sclerotium rolfsii) is a soilborne basidiomycetous fungus. It is a highly destructive pathogen globally, recognized by its ability to produce abundant white mycelium and characteristic mustard-seed-sized sclerotia that persist in the soil for years.

Diseases and crops: This fungus causes Southern blight, also known as white mold or crown rot. It has a broad host range, infecting hundreds of plant species including legumes, solanaceous crops like tomatoes and peppers, and various ornamental plants, leading to severe economic losses in both open fields and protected greenhouse environments.

Biology and life cycle: The pathogen survives in the form of sclerotia or mycelium in plant debris. When environmental conditions become favorable, the sclerotia germinate and form hyphae that invade the host tissue. The fungus secretes oxalic acid and cell-wall-degrading enzymes, causing rapid tissue necrosis and colonization of the plant collar region.

Development and spread conditions: A. rolfsii thrives in warm, humid climates, with optimal disease development occurring at temperatures between 25°C and 35°C. The pathogen spreads primarily through contaminated soil movement, water runoff, infected seedlings, and agricultural machinery, making it difficult to contain once established in a field.

Economic impact and management: Infected plants show sudden wilting, often followed by complete decay of the crown and death. Effective management is complex and requires an integrated approach:

• Rotation with non-host crops, such as corn or other cereals.
• Deep plowing to bury sclerotia deep into the soil profile.
• Application of systemic fungicides targeting soilborne pathogens.
• Maintaining soil drainage to reduce humidity around the base of plants.
• Biological control using Trichoderma species to antagonize the pathogen.