Grey Mould

Botrytis cinerea

1. Identification

Grey mould is a fungal disease of great economic importance, affecting agricultural, ornamental and forest crops. It is characterised by the formation of a powdery greyish‑brown coating, composed of conidiophores and conidia, which appears on flowers, leaves, fruits and senescent or wounded tissues. The fungus develops as an opportunistic necrotroph, preferentially colonising weakened, wounded tissues or those subjected to high humidity.

2. Causal agent

The genus Botrytis was described by Micheli (1729), with Botrytis cinerea being the most relevant and widely distributed species.

• Ascomycete fungus of the family Sclerotiniaceae.
• It produces superficial and internal mycelium, branched conidiophores and hyaline to greyish conidia.
• It forms black sclerotia, responsible for survival under adverse conditions.
• High capacity for infection in wounded, senescent tissues or those subjected to prolonged humidity.
• Dissemination mainly by conidia carried by wind, water or contact.

3. Main hosts

• Grapevine (Vitis vinifera).
• Strawberry (Fragaria × ananassa).
• Tomato (Solanum lycopersicum).
• Perishable vegetables (lettuce, bean, onion, among others).
• Various ornamentals (roses, gerberas, chrysanthemums).
• Forest and shrub species under conditions of high humidity.
• Floral tissues and ripe fruits are particularly susceptible.

4. Symptoms

• Watery spots that develop into brown necroses.
• Development of grey mycelium and a powdery mass of conidia on infected tissues.
• Wilting and drop of petals, flowers and young fruits.
• Soft rot in fruits, often with concentric rings of sporulation.
• Formation of black sclerotia on dead tissues or plant debris.
• In post‑harvest, rapid deterioration of fruits and vegetables.

5. Disease cycle

• Survival as sclerotia in the soil, plant debris or growing structures.
• Release of conidia under conditions of high humidity and moderate temperatures.
• Infection through wounds, stomata or senescent tissues.
• Rapid development in humid environments, with continuous production of conidia.
• Dissemination by wind, water splashes, insects or contact between plants.
• Formation of new sclerotia at the end of the cycle.

6. Favourable conditions

• High relative humidity (above 90%).
• Presence of free water on plant surfaces.
• Moderate temperatures (15–22 °C).
• High plant density and poor air circulation.
• Pruning wounds, mechanical damage or senescent tissues.
• Protected environments (greenhouses) with frequent condensation.

7. Disease management

• Removal of infected tissues and plant debris to reduce the inoculum.
• Improvement of ventilation and reduction of humidity through pruning and adequate spacing.
• Avoid excessive wetting of the foliage and condensation in greenhouses.
• Careful handling to avoid wounds on fruits and flowers.
• Use of less susceptible varieties when available.
• Monitoring of critical environmental conditions and preventive application of authorised protection measures.

Bibliographic references

• Dean, R., Van Kan, J. A. L., Pretorius, Z. A., et al. (2012). The Top 10 fungal pathogens in molecular plant pathology. Molecular Plant Pathology, 13, 414–430.
• Veloso, J., & van Kan, J. A. L. (2018). Many shades of grey in Botrytis–plant interactions. Trends in Plant Science, 23, 613–622.
• Williamson, B., Tudzynski, B., Tudzynski, P., & van Kan, J. A. L. (2007). Botrytis cinerea: the cause of grey mould disease. Molecular Plant Pathology, 8, 561–580.
• Fillinger, S., & Elad, Y. (2016). Botrytis – the Fungus, the Pathogen and its Management in Agricultural Systems. Springer.
• van Kan, J. A. L. (2006). Licensed to kill: the lifestyle of a necrotrophic plant pathogen. Trends in Plant Science, 11, 247–253.