Pellicularia rolfsii

Pellicularia rolfsii (often identified by its anamorphic stage Sclerotium rolfsii) is a destructive soil-borne fungal pathogen. Classified under the kingdom Fungi, this organism is the primary cause of southern blight, a devastating disease affecting a vast array of crops, including legumes, vegetables, fruits, and ornamental plants in warmer regions globally.

The disease typically presents as rapid wilting and chlorosis of the foliage, followed by the rotting of the crown and root system. A diagnostic feature of this infection is the visible white, fan-like mycelial growth spreading over the soil surface and the lower parts of the stem. As the fungus matures, it produces numerous small, round, mustard-seed-like sclerotia, which serve as its primary survival and dispersal structures.

The biology of this pathogen is centered around the sclerotia, which allow it to persist in the soil for several years. Upon stimulation by root exudates under high temperature and moisture conditions, these sclerotia germinate. The fungus acts as a necrotrophic pathogen, secreting a complex cocktail of oxalic acid and cell wall-degrading enzymes that macerate host tissue, leading to plant death.

Pellicularia rolfsii thrives in environments where soil temperatures range between +25°C and +35°C and humidity is consistently high. Due to its wide host range—infecting over 500 plant species—it is highly difficult to manage through simple crop rotation. It easily spreads via contaminated agricultural machinery, irrigation water, and the movement of infested soil particles.

Integrated management is essential for controlling this pathogen. This includes the use of certified disease-free seeds and transplants, deep plowing to bury sclerotia below the germination zone, and maintaining optimal soil drainage. Chemical control involves the application of appropriate fungicides targeting soil-borne pathogens, often integrated with cultural practices like solarization to reduce the inoculum density in the field.