Onion Botrytis neck rot

Botrytis byssoidea is a destructive fungal pathogen belonging to the Kingdom Fungi, genus Botrytis. It is widely recognized in agronomy as a primary causative agent of neck rot in Allium crops. This fungus is specifically adapted to invade the succulent tissues of onion bulbs, leading to severe post-harvest losses and quality degradation.

The primary symptom of the disease is the softening and browning of the neck tissues of the onion bulb. As the infection progresses, a dense, cottony white mycelium develops between the scales of the bulb. Eventually, the infected tissues collapse, and the entire bulb becomes a rotted mass, which may also be colonized by secondary opportunistic bacteria.

The biological life cycle of Botrytis byssoidea involves the production of conidia that are wind-borne and water-splashed onto susceptible onion tissues. The fungus overwinters as sclerotia or dormant mycelium within infected crop debris or in the soil. These structures allow the pathogen to survive harsh environmental conditions and initiate new infections in the following growing season.

Optimal environmental conditions for the development of this pathogen include high relative humidity (above 85%) and moderate temperatures ranging from 15 to 20°C. In the field, excessive irrigation or rainfall during the bulb maturation stage significantly increases infection pressure. In storage, poor ventilation and high humidity are the primary drivers of rapid disease spread.

The economic impact of this pathogen is severe, as it can cause significant yield losses both in the field and during transit or storage. Effective control strategies involve an integrated approach: avoiding planting in poorly drained soils, ensuring adequate spacing for airflow, and harvesting during dry weather conditions. Post-harvest, rapid drying (curing) is essential to harden the outer scales and prevent fungal entry through the neck.