Didymella stem rot

The fungus is classified within the Ascomycota phylum. It survives as mycelium or pycnidia in crop debris, infested soil, and can be seed-borne, making sanitation a critical factor in disease management.

The disease primarily attacks tomato plants but can also infect other members of the Solanaceae family. It causes significant economic damage by destroying stems, leaves, and ripening fruits.

Severe infestations lead to total plant death or render the fruits unmarketable due to deep, necrotic lesions that compromise the structural integrity of the crop.

The pathogen thrives in warm, humid conditions. High humidity (above 85%) and temperatures ranging from 18°C to 24°C are optimal for spore production and infection spread.

Spores are dispersed by water splashes during irrigation, air currents, and physical contact with contaminated tools or workers. The disease cycle is continuous if environmental conditions remain favorable.

Symptoms often appear as dark, sunken lesions on the stem, typically near the soil line. As the infection progresses, the lesions expand, girdling the stem and causing the plant to wilt.

On fruits, the infection starts near the stem attachment point, resulting in dark, firm, sunken spots with concentric rings.

• Wilting of lower leaves is a common early indicator.
• Small, dark pycnidia (fruiting bodies) become visible within the lesion area.

Integrated pest management is essential for controlling Didymella. This includes using certified disease-free seeds and performing rigorous crop rotation to avoid pathogen buildup in the soil.

Maintaining proper ventilation and humidity control in greenhouses helps suppress fungal growth. Preventive fungicide applications are recommended in high-risk areas, ensuring thorough coverage of the base of the stems.