Thanatephorus cucumeris

This fungus is a necrotrophic pathogen with a very broad host range. It affects numerous economically important crops including potatoes, tomatoes, beans, brassicas, and various ornamental plants. It primarily attacks roots, stems, and tubers.

The damage caused by this pathogen includes seedling death (damping-off), root decay, and stem lesions. It can destroy entire fields if the environmental conditions favor its development and the soil inoculum density is high.

The development of the fungus is highly dependent on environmental moisture and soil temperature. It thrives in conditions with high soil humidity and temperatures ranging from 15°C to 25°C.

The fungus survives as sclerotia (hard, dark fungal masses) or mycelium in the soil or on infected plant debris for years. It spreads rapidly through soil movement, contaminated tools, or infected nursery stock.

Common symptoms of infection include:

• Black scurf on potato tubers.
• Damping-off of young seedlings at the soil surface.
• Sunken brown lesions on roots and lower stems.
• Formation of a white, cobweb-like mycelial mat on stems in humid conditions.
• Reduced vigor and stunted plant growth due to compromised root systems.

Management strategies involve crop rotation with non-host crops and improving soil drainage to reduce humidity. Removing crop residues after harvest significantly reduces the inoculum level in the soil.

Chemical control includes the application of effective fungicides as seed or tuber treatments at planting. Proper soil pH management and the use of balanced fertilization also help in reducing the incidence and severity of the disease.