Sweet potato stem rot

The causal agent of sweet potato stem rot and dry rot is the fungal pathogen Diaporthe destruens (syn. Phoma batatae). This pathogen poses a significant threat to sweet potato production worldwide, primarily affecting the roots both in the field and during storage.

The primary host for this fungus is the sweet potato (Ipomoea batatas). The disease is particularly problematic because it can remain latent on planting materials or persist in the soil for several seasons, causing recurring outbreaks if proper sanitation is not strictly observed.

Symptoms of the infection typically appear as sunken, dark-brown, or black lesions on the surface of the storage roots. As the disease progresses, the internal tissue becomes spongy and dry, eventually causing the entire root to rot. If the infection reaches the stem base, it can cause stunting and wilting of the vines.

The development of Diaporthe destruens is highly favored by high moisture levels and moderate temperatures. The fungus spreads through infected planting slips (vines used for propagation), infested soil, and debris left in the fields. Wounds created during harvesting provide an easy entry point for the spores.

Preventive measures are the cornerstone of disease management. Farmers should prioritize the use of disease-free propagation material and practice crop rotation, avoiding Solanaceae or Convolvulaceae crops for several years. Ensuring quick healing of harvest wounds (curing) and maintaining clean, well-ventilated storage environments significantly reduces the risk of post-harvest decay.