Sclerotinia

Sclerotinia spp.

1. Identification

Sclerotinia spp. is a group of pathogenic fungi responsible for white rots and wilting in various horticultural and ornamental crops. The most relevant species are Sclerotinia sclerotiorum and Sclerotinia minor, both capable of causing significant losses.

2. Causal agent

Ascomycete fungi of the genus Sclerotinia, described by Fuckel, characterised by the formation of hard, black sclerotia, which act as resistance structures in the soil. They produce white, cottony mycelium and, under favourable conditions, apothecia that release ascospores.

3. Main hosts

• Leafy vegetables: lettuce, chard, spinach
• Fruiting vegetables: tomato, pepper, cucurbits
• Legumes: bean, pea
• Various ornamentals
  The group has a very broad host spectrum, affecting more than 400 species.

4. Symptoms

• White, wet rot in the tissues
• Dense, white mycelium on the surface of the lesions
• Formation of black sclerotia
• Sudden wilting and collapse of plants
• Post-harvest rots in sensitive fruits

5. Disease cycle

The sclerotia germinate in two ways:

• Carpogenic → formation of apothecia and release of ascospores
• Myceliogenic → direct infection of tissues in contact with the soil
  Infection is favoured by high humidity, moderate temperatures and weakened tissues.

6. Favourable conditions

• High humidity and prolonged leaf wetness
• Moderate temperatures (15–20 °C)
• High plant density and poor ventilation
• Soils rich in organic matter and poorly drained
• Accumulation of sclerotia over several crop cycles

7. Disease management

• Prevention: avoid excess humidity and improve ventilation
• Rotation: avoid susceptible crops in succession
• Sanitation: remove infected plants and contaminated residues
• Soil management: avoid waterlogging and excess fresh organic matter
• Integrated protection: less susceptible varieties, appropriate spacing, monitoring
• Biological control: use of authorised antagonists
• Chemical control: only with approved products and according to local regulations

Bibliographic references

• Bolton, M. D., Thomma, B. P. H. J., & Nelson, B. D. (2006). Sclerotinia sclerotiorum: Biology and Pathogenicity.
• Agrios, G. N. (2005). Plant Pathology. Elsevier.
• EPPO. Diagnostic Protocols for Sclerotinia spp.
• FAO. Guidelines for Integrated Disease Management in Horticultural Crops.