Punky rot of sweet potato

Punky rot, caused by the fungus Trichoderma koningii, is a destructive postharvest disease affecting sweet potato roots. While many Trichoderma species are beneficial in soil ecosystems, T. koningii acts as a significant pathogen during storage, leading to substantial economic losses.

The disease is characterized by the internal breakdown of the root tissues. Once the pathogen enters the root through wounds or bruises occurring during harvest, it colonizes the interior, causing the flesh to become soft, spongy, and prone to rapid decomposition.

The primary symptom is the emergence of a fluffy, white-to-greenish fungal growth on the surface of the root. This mass is composed of dense mycelium and spores, which serve as the primary source of inoculum for spreading the rot to adjacent healthy tubers in storage.

Environmental conditions are critical for disease development. High relative humidity and temperatures exceeding 20°C significantly accelerate the progression of the fungus. Poor ventilation in storage crates or bins creates the perfect microclimate for the rapid colonization of the pathogen.

Effective management requires strict adherence to postharvest protocols:

• Carefully handling roots during harvest to avoid wounding.
• Proper curing of sweet potatoes for 4–7 days at 27–30°C to heal surface damage.
• Maintaining storage temperatures between 12–15°C and relative humidity at 85–90%.
• Ensuring adequate airflow to prevent moisture accumulation.