White rot

Sclerotinium cepivorum

Appearance and Symptoms:

Sclerotium cepivorum is a soilborne fungus that causes white rot disease in Allium species, including onions and garlic. The disease affects various plant parts and can cause significant yield losses. Here's an informative description:

  1. White Mycelial Growth: The initial symptom involves the development of a white, fluffy mycelial growth on the basal plate and lower leaves of the infected plants.

  2. Sclerotia Formation: The fungus produces small, round, and hard structures called sclerotia. These are initially white but turn dark as they mature. Sclerotia are survival structures that can persist in the soil for several years.

  3. Decomposition of Tissues: As the disease progresses, the mycelium invades and decomposes the infected tissues, including bulbs or cloves.

Identification:

  1. White Mycelium: Look for the characteristic white mycelial growth at the base of plants and on lower leaves.

  2. Sclerotia Presence: Check for the formation of small, hard, and initially white sclerotia. These can be found in and around the infected tissues.

  3. Rotting Bulbs or Cloves: Presence of soft, watery decay in bulbs or cloves, often accompanied by a foul odor.

Disease Cycle:

  1. Survival: Sclerotia survive in the soil between crops, serving as a source of inoculum for subsequent plantings.

  2. Infection: The fungus infects plants through wounds or natural openings. Infection is favored by cool, wet conditions.

  3. Sclerotia Production: The fungus produces new sclerotia within infected tissues, contributing to the soilborne inoculum.

Management:

Cultural Practices:

  1. Crop Rotation: Avoid planting Allium crops in the same field year after year to reduce the buildup of the pathogen.

  2. Proper Irrigation: Avoid overwatering and ensure proper drainage to minimize favorable conditions for disease development.

Sanitation Practices:

  1. Removal of Infected Debris: Remove and destroy infected plant debris after harvest to reduce the presence of sclerotia in the soil.

  2. Sclerotia Reduction: Plowing or tilling the soil can help bury sclerotia deeper, making them less accessible to future crops.

Resistant Varieties:

  1. Plant Resistant Varieties: Use onion or garlic varieties that have some level of resistance to Sclerotium cepivorum.

Chemical Control:

  1. Fungicide Application: Fungicides may be applied preventively, but their efficacy can be limited, and they are often more effective as part of an integrated management strategy.