Didymella stem rot of tomato

The causal agent of this disease is the fungus Didymella calidophila, which belongs to the class of ascomycetes. This pathogen is responsible for a serious infection known as Didymella stem rot, which primarily affects solanaceous crops, specifically tomatoes, in both greenhouse and open-field conditions.

Tomatoes are the main host for this pathogen. The fungus invades the plant tissues through micro-cracks or physical damage. The pathogen can survive in crop debris, soil, and even on seeds, making it highly resilient and capable of persisting through unfavorable environmental conditions for long periods.

Symptoms of the infection typically appear as dark, often sunken lesions on stems, leaf petioles, and fruits. Over time, these lesions expand and can girdle the stem, leading to wilting and eventual death of the entire plant or individual branches due to the disruption of vascular transport systems.

High humidity and moderate temperatures are the primary factors that facilitate the development and rapid spread of the disease. Overhead irrigation, lack of proper ventilation in greenhouses, and high plant density create an ideal microclimate for the formation and germination of fungal spores, accelerating the spread to adjacent healthy plants.

The economic impact of Didymella stem rot includes significant yield reduction and loss of fruit quality. In cases of severe infestation, large portions of the crop can be lost. Preventive measures include using certified disease-free seeds, strict adherence to crop rotation, regular disinfection of greenhouse structures, and the prompt removal of infected plant debris. Chemical control involves the application of appropriate fungicides during the growing season at the first signs of the pathogen.