Sclerotinia sclerotiorum is a phytopathogenic fungus that causes diseases known as white mold, white rot or sclerotinia wilt. These names derive from the characteristic symptoms of the disease in affected plants.
Crops attacked
Sclerotinia sclerotiorum It has a wide host range, affecting more than 400 plant species.
Among the crops of economic importance are soybeans, beans, sunflowers, cotton, canola, potatoes, tomatoes and lettuce.
The disease has been reported in several producing regions of Brazil, causing significant losses.
Symptoms
Initial symptoms include water-soaked lesions on the aerial parts of plants, which progress to rot and wilting.
The presence of cottony white mycelium is observed on the surface of infected tissues.
Subsequently, sclerotia are formed, dark-colored resistance structures, both internally and externally in the attacked parts.
These symptoms can lead to the death of the plant if left unchecked.
Etiology and characteristics
Sclerotinia sclerotiorum is a phytopathogenic fungus belonging to the phylum Ascomycota and the family Sclerotiniaceae. It is one of the main agents causing diseases in several agricultural crops due to its wide host range and ability to survive in the soil for long periods.
The fungus spreads and survives in the environment through sclerotia, resistant structures composed of dense, melanized fungal tissue. These structures:
- They allow the pathogen to survive in the soil for up to 10 years, even in the absence of host plants.
- They germinate under favorable environmental conditions, resulting in the production of infective mycelium or apothecia, which release spores.
Germination of sclerotia occurs through two main processes:
- Myceliogenic Germination:
The sclerotia directly produces mycelium, which grows and infects adjacent plant tissues.
This type of infection occurs mainly when there is direct contact between the sclerotia and the plant.
- Carpogenic Germination:
The sclerotium forms apothecia, small cup-shaped structures, which produce and release ascospores into the air.
These spores are dispersed by the wind and can infect plants from a distance.
Carpogenic germination occurs preferably in conditions of high humidity and temperatures between 10°C and 25°C.
The fungus can infect the plant in different ways:
- Direct infection: the germinated sclerotia mycelium penetrates the plant tissues through wounds or contact with senescent tissues.
- Ascospore infection: these spores settle on flowers, leaves and stems, germinate and colonize the tissues, promoting infection.
- Production of enzymes and toxins: the fungus releases hydrolytic enzymes and toxins that destroy the plant's cell wall, facilitating the spread of the pathogen and causing tissue necrosis.
The occurrence of the disease is influenced by climatic and management factors. Ideal conditions for infection include:
- High relative humidity (> 80%).
- Moderate temperatures between 15°C and 25°C.
- High plant density, which reduces ventilation and increases humidity in the canopy.
- Presence of infected crop remains, which serve as the primary source of inoculum.
Sclerotinia sclerotiorum is highly adaptable and resistant, featuring:
- Ability to form sclerotia in any infected part of the plant, ensuring the perpetuation of the fungus in the soil.
- Lack of host specialization, allowing infection of hundreds of plant species.
- High sporulation potential, increasing the spread of the pathogen by wind.
These factors make white mold a difficult disease to control, requiring integrated management strategies to reduce its incidence in crops.
Control
Integrated management is essential for effective control of white mold. Recommended measures include:
- Crop rotation: avoid successive planting of susceptible crops in the same area, opting for non-host species to reduce inoculum in the soil.
- Biological control: use antagonistic agents, such as fungi of the genus Trichoderma, which compete with S. sclerotiorum and reduce the viability of sclerotia.
- Cultural management: adopt practices such as adequate spacing between plants to improve aeration, use of soil cover with grass straw to prevent sclerotia germination and elimination of infected crop residues.
- Chemical control: apply fungicides preventively, especially during the flowering period, when plants are most susceptible to infection.
The implementation of these strategies in an integrated manner is essential to minimize the damage caused by Sclerotinia sclerotiorum and ensure the sustainability of affected agricultural crops.
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