Bitter rot of apple

The disease known as bitter rot is caused by the fungus Gloeosporium laeticolor. This pathogen is a significant threat to pomaceous crops, primarily apples and pears, acting as both an orchard-borne infection and a destructive post-harvest disease that can ruin stored fruit stocks within a short period.

The pathogen targets the fruit of apple trees. Infection often occurs during the growing season when spores produced on mummified fruit or diseased twigs are splashed by rain onto healthy fruit. The fungus can penetrate the skin through wounds or natural openings such as lenticels, where it may remain dormant until conditions trigger its development.

Visible symptoms include circular, sunken, brown or tan lesions on the fruit surface. As the infection progresses, the lesions enlarge, often showing concentric rings of fruiting bodies that release spores. In advanced stages, the fruit flesh becomes soft and decayed, frequently resulting in a bitter taste, which is why it is commonly referred to as bitter rot.

The proliferation of Gloeosporium laeticolor is heavily dependent on warm, humid weather conditions. Prolonged rainfall during the summer months facilitates the dispersion of spores throughout the tree canopy. The fungus overwinters in dead wood, cankers, and infected fruit remnants, ensuring a constant source of inoculum for the next season.

Effective management requires an integrated approach to mitigate damage:

• rigorous sanitation, including the removal of mummified fruit and pruning of infected wood;
• application of protective and systemic fungicides during the growing season;
• monitoring fruit during the pre-harvest period;
• maintaining low temperatures and proper aeration in storage facilities to slow down lesion development.