Sour rot

The primary symptom is the appearance of water-soaked, softening lesions on the fruit surface. These spots expand rapidly, causing the internal tissue to lose its integrity and turn into a soft mass.

A distinctive feature of the disease is a sharp, acidic, or vinegary smell caused by the fermentation processes of the fungus. Unlike other rots, surface growth is often sparse and subtle.

Over time, a fine, white, or creamy fungal growth may appear on the affected areas. This mycelial mat is usually delicate and covers the decaying tissue like a thin film.

In grapevines, sour rot typically originates in injured berries, spreading rapidly through the cluster. The berries become translucent and mushy, often attracting fruit flies.

For citrus and peaches, the skin quickly separates from the pulp as the fruit collapses. The rapid rate of decay means entire harvests can be lost in just a few days if conditions are ideal for the fungus.

The causal agent of this disease is the fungus Geotrichum candidum, a ubiquitous soil-borne microorganism. It can function both as a saprotroph, decomposing organic matter, and as a pathogen invading living plant tissues.

The fungus produces abundant mycelium that easily fragments into arthrospores. These spores serve as the primary means for the rapid spread of the disease within orchards and vineyards.

Equipped with potent enzymatic activity, the pathogen efficiently breaks down plant cell walls. It shows high resilience to environmental fluctuations, allowing it to persist in soil and crop debris for extended periods.

The host range is extensive, including citrus, peaches, and grapevines. It often behaves as an opportunistic secondary pathogen, infecting tissues that have already been weakened by pests or primary diseases.

In post-harvest facilities, Geotrichum candidum is highly aggressive, capable of causing devastating losses in stored produce if hygiene standards are neglected.

High relative humidity (above 85%) and warm temperatures between +20°C and +28°C create the perfect environment for the fungus to thrive. These conditions significantly accelerate the disease cycle.

Mechanical damage is the most critical factor for infection. Wounds caused by hail, insect pests (such as moths or wasps), or careless harvesting provide direct access for fungal spores to penetrate.

Poor ventilation in storage facilities and the formation of condensation on fruit surfaces are major catalysts for outbreaks. Close contact between infected and healthy fruit facilitates rapid transmission.

In the field, dense canopy structures that trap moisture and reduce airflow create localized microclimates that are highly favorable for infection.

Overripe or senescing fruit are particularly susceptible and act as initial reservoirs of inoculum, which then spreads to healthier fruit in the vicinity.

Sour rot causes a total loss of commercial marketability. Affected fruits become unfit for sale or processing, leading to significant economic losses for growers and packers.

In winemaking, the infection ruins the quality of the must. Even a small proportion of infected grapes can impart off-flavors and undesirable acidity to the entire batch of wine.

The disease requires intensive management, including higher costs for fungicide applications and rigorous sorting processes during harvest to prevent the contamination of healthy lots.

Chronic presence of the pathogen in orchards can weaken overall tree health, reducing yields in subsequent seasons and necessitating long-term sanitary interventions.

The attraction of insect pests to rotting fruit creates a feedback loop, as these insects further damage fruit and vector additional diseases throughout the plantation.

Integrated pest management (IPM) is essential to control insects that wound fruit, as preventing mechanical injury is the most effective way to limit infection.

Strict orchard hygiene is vital: promptly remove and destroy all decaying or mummified fruit to reduce the overwintering inoculum potential in the field.

Improve canopy management through proper pruning to enhance airflow and light penetration. This reduces humidity within the foliage and discourages fungal development.

Handle fruit with extreme care during harvesting to avoid bruising or skin breakage. Implement rigorous sorting protocols to ensure that damaged produce is discarded before storage.

Maintain optimal temperature and humidity levels in storage facilities, supported by continuous ventilation to prevent the condensation that triggers sour rot outbreaks.