Sclerotinia sclerotiorum

Sclerotinia sclerotiorum

Sclerotinia sclerotiorum sclerortia

Cluster of Apothecia

Sclerotinia sclerotiorum at Phaseolus vulgaris, sclerotiënrot stamsperzieboon

Sclerotinia sclerotiorum is a species of fungus in the family Sclerotiniaceae. It is a plant pathogen that affects a wide range of crop plants, including many important agricultural and horticultural species. This fungus is notorious for causing the disease known as white mold or sclerotinia rot, which can lead to significant losses in yield and quality in affected crops.

Description

Sclerotinia sclerotiorum produces characteristic black, hard structures called sclerotia, which are composed of dense masses of hyphae. These sclerotia can survive in the soil for several years, serving as a primary inoculum source for new infections. The fungus can infect plants at various stages of growth, leading to symptoms such as wilting, stem rot, and the development of a white, cottony mycelium on the surface of infected tissues. Under humid conditions, large numbers of sclerotia can form within this mycelium.

Life Cycle

The life cycle of Sclerotinia sclerotiorum involves both asexual and sexual phases. The sclerotia germinate under suitable environmental conditions, either directly by producing mycelial growth that infects the host plant or indirectly by producing small, mushroom-like structures called apothecia. The apothecia release ascospores, which are spread by wind and can infect plants over long distances. After infecting a plant, the fungus grows through the tissue, producing more sclerotia, which fall to the ground and can survive until the next growing season.

Host Range and Impact

Sclerotinia sclerotiorum has a broad host range, affecting over 400 plant species across many families. Significant crops impacted include sunflower, soybean, canola, beans, lettuce, and various ornamental plants. The disease can cause severe yield losses, especially in dense plantings where air circulation is poor and humidity is high. Management of white mold is challenging and often involves integrated approaches, including crop rotation, the use of resistant varieties, and timely application of fungicides.

Management

Effective management of Sclerotinia sclerotiorum requires an integrated approach:

• Cultural Practices: Crop rotation with non-host crops can reduce the number of viable sclerotia in the soil. Improving air circulation within the crop canopy by spacing plants appropriately can help reduce humidity and the risk of infection.
• Resistant Varieties: The use of plant varieties that are resistant or less susceptible to white mold is a key strategy in managing the disease.
• Chemical Control: Fungicides can be effective, especially when applied at the correct time for preventing infection or when the first symptoms appear. However, reliance on chemical control alone is not sustainable in the long term due to potential development of resistance.
• Biological Control: There is ongoing research into biological control agents that can suppress Sclerotinia sclerotiorum by outcompeting it or directly inhibiting its growth.

Conclusion

Sclerotinia sclerotiorum is a significant pathogen with a wide host range, capable of causing extensive damage to many crops. Its management is complex and requires an integrated approach, combining cultural, genetic, chemical, and biological strategies. Ongoing research into the biology and control of this pathogen is essential for developing more effective and sustainable management practices.