Sclerotinia rot of onion

The causative agent of Sclerotinia rot in onions is the fungus Sclerotinia allii. This pathogen is a significant threat to Allium species, causing severe damage to bulbous crops both in the field during the growing season and in storage facilities after harvest.

The primary symptom of the disease is the development of a white, cotton-like mycelial growth on the basal plate and outer scales of the onion bulb. As the infection progresses, the fungus produces hard, black structures known as sclerotia, which act as the primary survival mechanism in the soil for several years.

Environmental conditions such as high soil moisture and moderate temperatures are ideal for the rapid spread of Sclerotinia allii. The fungus is often introduced into fields through infested soil, contaminated planting stock, or infected crop residues left over from previous seasons in the field.

The economic impact of this disease is substantial, as infected bulbs soften and decay rapidly, leading to significant yield losses. Affected plants often exhibit wilting, yellowing of foliage, and a compromised root system, rendering the crop unmarketable and susceptible to further rot in storage.

To effectively manage and prevent the spread of this pathogen, farmers should implement the following strategies:

• Practice crop rotation with non-host crops for at least 4–5 years.
• Use certified, pathogen-free bulbs for planting.
• Improve soil drainage to prevent waterlogging and high humidity levels.
• Rigorously remove and destroy all infected plant material from the field.
• Apply appropriate fungicides as a preventive measure in high-risk areas.