Didymella stem rot

Systematic position and nature of the pathogen. Didymella lycopersici is a fungal pathogen belonging to the kingdom Fungi and the phylum Ascomycota. This pathogen is also recognized by its anamorph stage, Phoma lycopersici. It is a highly specialized parasite that poses a significant threat to solanaceous plants, specifically within the greenhouse industry.

Diseases and host range. The pathogen causes a disease known as Didymella stem rot or Phoma rot. While tomatoes are the primary host, the fungus is capable of infecting peppers, eggplants, and various solanaceous weeds. The disease manifests across all plant structures, causing stem lesions, leaf spots, and fruit decay.

Biology and lifecycle. The fungus overwinters in crop debris, soil, and infected seeds as pycnidia and perithecia. During favorable conditions, spores are disseminated via water splash, irrigation, wind, or contaminated equipment. Infection typically occurs through wounds, particularly those made during pruning or handling, where the mycelium then invades the plant tissue.

Developmental conditions and impact. High relative humidity (over 85%) and moderate temperatures (18-22°C) facilitate the rapid development of the disease. The pathogen causes characteristic dark, sunken lesions on stems, leading to wilting and death of the plant. In extreme cases, crop losses can be devastating, making early detection and intervention critical for agricultural productivity.

Protection and control measures. Management of Didymella requires a multi-faceted strategy:

• Sourcing high-quality, certified, and pathogen-free seeds.
• Implementing crop rotation to prevent the buildup of soil-borne inoculum.
• Sanitation practices, including the removal and destruction of all infected crop residues.
• Optimizing greenhouse ventilation to reduce humidity levels during the growing season.
• Applying targeted fungicides, such as those containing copper compounds or triazoles, to prevent and mitigate initial infections.