Sour skin of onion

The causative agent of the disease known as "sour skin" is the phytopathogenic bacterium Burkholderia cepacia. This is a severe bacterial disease that most frequently manifests during the storage period or when preparing onion bulbs for distribution. The bacterium enters plant tissues through mechanical wounds or the root system, triggering rapid enzymatic degradation of the tissues.

The primary crops affected by this pathogen include onion and garlic. The infection may occur latently under field conditions but often accelerates rapidly post-harvest, especially if curing processes or temperature control during storage have been compromised. In temperate climates, this disease poses a significant threat to the commercial quality and shelf life of the crop.

A hallmark symptom of the infection is the softening of the onion scales, which take on a watery, translucent appearance. When an infected bulb is cut, it emits a distinct sour odor, which gives the disease its common name. Over time, internal tissues decay into a yellow or brown mush, and in advanced stages, the entire bulb may be reduced to a foul-smelling, semi-liquid mass.

Development of Burkholderia cepacia is favored by high soil moisture levels during crop maturation and prolonged rainfall during harvest. The optimal conditions for the spread of the infection in storage facilities are high temperatures combined with poor aeration. The bacteria spread rapidly from infected bulbs to healthy ones through direct contact or water film, leading to substantial post-harvest losses.

The economic impact is primarily due to product spoilage in storage, rendering the harvest unmarketable. Managing "sour skin" requires an integrated strategy to minimize pathogen pressure:

• Practicing strict crop rotation, allowing a gap of at least 3-4 years between susceptible crops.
• Ensuring thorough drying and curing of bulbs immediately after harvest until the neck is fully sealed.
• Using high-quality, disease-free planting material and resistant cultivars.
• Maintaining storage temperatures close to 0°C with adequate ventilation and humidity control.
• Regular sanitation and disinfection of storage facilities and handling equipment.