Botrytis neck rot of onion

Botrytis neck rot is a destructive fungal disease caused by the pathogen Botrytis aclada. This fungus is a serious threat to onion production globally, particularly affecting the quality and shelf-life of bulbs. The pathogen is highly adapted to infecting onion tissues, often remaining asymptomatic during the initial phases of plant growth.

The primary host for Botrytis aclada is the common onion (Allium cepa), but it can also infect leeks, shallots, and garlic. The fungus typically gains entry through the neck tissue of the onion during the maturation and harvesting process, especially when the neck remains thick and fleshy due to improper growing conditions or moisture.

Key symptoms include the softening and water-soaking of the tissue at the neck of the bulb. As the infection progresses, the scales become soft and may develop a gray, fuzzy mold consisting of conidia and conidiophores. Eventually, hard, black structures known as sclerotia develop, serving as the primary overwintering and survival mechanism for the pathogen.

The development of neck rot is heavily influenced by environmental conditions. High humidity and cool, rainy weather during the late maturation stage significantly increase disease pressure. In storage, poor ventilation and high moisture content allow the fungus to spread rapidly from infected bulbs to healthy ones, potentially destroying an entire storage lot.

Effective management requires an integrated approach. Farmers should prioritize the use of disease-free sets, appropriate fertilization to avoid delayed maturity, and timely harvesting during dry weather. Post-harvest, rapid and thorough curing of the bulbs is the most critical step to seal the neck tissues and prevent fungal colonization.

• Maintain low humidity and proper air circulation in storage units.
• Remove and destroy infected bulbs immediately upon detection.
• Practice crop rotation to break the fungal life cycle in the soil.
• Use recommended fungicides during the growing season if weather forecasts predict persistent wet conditions.