Sclerotinia minor

The fungus Sclerotinia minor is a soil-borne pathogen responsible for significant losses in various agricultural crops. It is taxonomically distinct from Sclerotinia sclerotiorum primarily due to its smaller sclerotia, which are the resting structures used by the fungus to survive in the soil. This pathogen mainly attacks the crown and root system of susceptible plants, leading to rapid tissue decay.

This disease affects a wide array of hosts, including lettuce, carrots, celery, beans, and peanuts. Because it is highly polyphagous, Sclerotinia minor can persist in agricultural soils for many years, infecting a broad spectrum of vegetable and ornamental crops. Its ability to survive as sclerotia in the soil makes it a particularly persistent threat for farmers.

Symptoms of the infection typically begin as water-soaked lesions near the soil line on the stems or leaf bases. As the disease progresses, a dense, white, cottony mycelium develops on the affected tissues. A key diagnostic feature is the presence of numerous small, black, irregularly shaped sclerotia, usually less than 2 mm in size, embedded within the rotten tissue.

The development and spread of Sclerotinia minor are heavily favored by cool, moist conditions. Unlike other species that rely on airborne ascospores, this pathogen primarily infects through the germination of sclerotia in contact with plant tissue. High soil moisture and moderate temperatures provide the ideal environment for the fungus to colonize and destroy the plant crown.

Effective management strategies focus on reducing the inoculum density in the soil and preventing favorable conditions for fungal growth. Key practices include

• long-term crop rotation with non-host crops;
• improving field drainage and spacing to reduce canopy humidity;
• using biological control agents like Coniothyrium minitans;
• thorough removal and disposal of infected plant debris.