Southern blight

Taxonomic position and pathogen type: Sclerotium rolfsii (teleomorph: Athelia rolfsii) is a destructive soil-borne fungal pathogen belonging to the class Agaricomycetes. It is characterized by the production of numerous sclerotia, which serve as long-term survival structures in the soil, allowing the fungus to persist in agricultural fields for many years.

Diseases and host crops: This pathogen causes southern blight (also known as white mold or southern stem rot). It is a highly polyphagous fungus, infecting more than 500 plant species including tomatoes, peppers, peanuts, beans, and various ornamental plants, leading to severe economic losses in both field and greenhouse settings.

Biology and life cycle: The infection begins when sclerotia germinate in response to root exudates or environmental triggers. The resulting white, fan-like mycelial mats spread across the soil surface and attack plant tissues at the soil line. The fungus produces oxalic acid and cell-wall degrading enzymes that rapidly break down plant cell walls, causing decay.

Environmental conditions and impact: Sclerotium rolfsii thrives in warm, moist environments, with optimal infection occurring at temperatures between 25°C and 35°C. High humidity levels significantly accelerate disease progress. The pathogen causes rapid wilting and collapse of the plant, often resulting in significant yield reduction or total destruction of the stand.

Protection and control measures: Managing southern blight is challenging due to the pathogen's ability to survive as sclerotia in the soil; therefore, an integrated approach is essential:

• Implementing crop rotation with non-host crops like corn or small grains.
• Deep plowing to bury sclerotia, which reduces their ability to reach the soil surface.
• Improving soil drainage to prevent conditions favorable for mycelial growth.
• Applying fungicides specifically labeled for soil-borne pathogen control.
• Utilizing biological control agents such as Trichoderma species to suppress the pathogen's colonization of the rhizosphere.