Diaporthe wilt of cassava

The disease is caused by the fungus Diaporthe manihotis, an ascomycete pathogen that primarily targets cassava plants. It is known to cause severe vascular wilt and stem dieback, impacting the overall vitality and development of the cassava crop in tropical regions.

Cassava (Manihot esculenta) is the primary host for this fungus. The pathogen colonizes the stem and vascular tissues, disrupting the plant's ability to transport water and essential nutrients, which is crucial for the formation and development of the starchy storage roots.

The symptoms of the infection include chlorosis, followed by wilting of the upper leaves. As the disease progresses, dark necrotic lesions appear on the stems, often encircling them. These lesions eventually cause the tissues above the infection site to die. Small, black pycnidia can frequently be observed within the necrotic areas.

The development and spread of Diaporthe manihotis are strongly favored by prolonged high humidity and warm temperatures. Rain splash is a primary mechanism for the dispersal of fungal spores within a field, allowing the pathogen to move rapidly from infected plant debris to healthy stems.

The economic impact of the disease is significant, as it leads to considerable yield losses in both biomass and tuber production. In severe cases, the death of main stems limits the accumulation of starch in the roots, making the harvest economically unviable and reducing the shelf life of the tubers.

Management strategies for this disease focus on integrated pest management practices. These include the use of clean, pathogen-free stem cuttings for planting and strict field sanitation to remove and destroy infected plant remains. Implementing crop rotation and maintaining proper plant spacing can also help reduce the humidity around the canopy, thereby limiting the success of fungal infection.