Yeast soft rot

Onions and garlic are the primary crops susceptible to this type of soft rot, particularly during prolonged storage periods in humid conditions.

The initial signs include water-soaked lesions on the scales, which gradually expand and become soft, often exhibiting a light tan or cream-colored appearance.

Affected tissues lose their structural integrity and become mushy, frequently releasing a distinct yeasty or slightly fermented odor that differentiates it from typical bacterial soft rots.

As the infection progresses, a white or cream-colored yeast growth may become visible on the surface of the scales, representing mass proliferation of the fungal cells.

The inner cloves of garlic or internal layers of the onion bulb quickly decay into a soft, semi-liquid mass, resulting in a total loss of commercial value.

The causative agent of this disease is the yeast-like fungus Kluyveromyces marxianus, an ascomycetous yeast known for its ability to metabolize simple sugars efficiently.

In agronomy, this pathogen is categorized as a post-harvest decay agent that affects various vegetable crops after they have been harvested and placed in storage.

The fungus produces enzymes that break down plant cell wall polysaccharides, which leads to the softening of tissues and the development of characteristic rot symptoms.

This pathogen is naturally occurring and can be found in soil and on debris, acting as a opportunistic colonizer that infects vegetables when physiological barriers are breached.

Biological studies of this yeast highlight its high thermotolerance, allowing it to remain active and cause significant damage even under fluctuating storage temperatures.

High relative humidity, typically exceeding 85 percent in storage environments, is the primary driver for the development and spread of this fungal rot.

The pathogen thrives at temperatures between +20°C and +30°C, making warm and poorly ventilated storage facilities particularly high-risk areas for infection.

Physical injuries, such as cuts or bruises sustained during the harvesting or handling process, provide essential entry points for the yeast to colonize the plant tissues.

Poor air circulation within storage crates or bulk bins leads to stagnant pockets of high humidity, which significantly accelerates the decay of healthy bulbs near the infected ones.

Harvesting crops under wet conditions without immediate and effective curing (drying) significantly increases the vulnerability of the produce to this yeast pathogen.

The main impact of yeast soft rot is severe post-harvest economic loss, as infected produce becomes unsalable and unsuitable for processing.

Because the disease spreads through contact, a single infected bulb can trigger a rapid breakout of rot throughout an entire storage crate or container.

The degradation of vegetable tissues alters the flavor and chemical profile, making the produce unusable for culinary applications even if the symptoms are localized.

Producers face significant costs related to labor for manual sorting and discarding of rotted produce to save the remaining healthy bulbs in a batch.

The disease complicates inventory management, forcing earlier disposal of stocks and increasing the overall risk profile of long-term vegetable storage.

Proper curing after harvest is the most critical step to prevent soft rot, as it ensures that the bulb skins are dry and resistant to fungal colonization.

Strict sorting before storage is essential to remove damaged or bruised onions and garlic that are highly susceptible to becoming primary infection sources.

Maintaining optimal storage temperatures (near +1°C to +3°C) and ensuring consistent, efficient airflow helps inhibit the growth of Kluyveromyces marxianus.

Regular sanitation of storage areas, including bins and ventilation systems, helps reduce the overall spore load in the facility environment.

• Implement precise moisture control systems in warehouses.
• Avoid overfilling containers to ensure adequate ventilation.
• Monitor stock regularly to identify and remove early infection signs.