Phoma gangrene

Phoma exigua (formerly often identified as Phoma solanicola) is the fungal pathogen responsible for Phoma gangrene in potatoes. This disease is a significant threat primarily during the storage phase, though it can also affect plants in the field during the growing season under specific environmental conditions.

The fungus primarily attacks potato tubers, but it can also infect other solanaceous crops. The pathogen survives in the soil as chlamydospores or pycnidia on crop debris and is introduced into storage facilities primarily via contaminated tubers harvested from infested fields.

Symptoms appear on the tubers as small, dark, slightly depressed lesions that gradually expand. As the lesion progresses, the affected tissue turns brown and dries out, often leaving cavities inside the tuber. The margin between the infected tissue and healthy flesh is usually distinct, and tiny black fruiting bodies (pycnidia) often appear on the surface of the lesions.

The development of the disease is favored by cool, moist conditions during the harvest period. Mechanical damage to the tuber skin is the primary entry point for the fungal spores. Once in storage, the infection can spread rapidly if humidity levels are high and ventilation is poor, particularly in damp and cool environments.

The economic impact of Phoma gangrene is severe, often resulting in heavy losses during the winter months when tubers are in storage. The reduction in marketability and the potential for total loss of specific batches make disease control essential. Management focuses on preventing tuber damage and maintaining optimal storage conditions to inhibit fungal growth.

• Selecting resistant potato varieties for cultivation
• Ensuring careful handling during harvest to minimize skin injuries
• Implementing strict crop rotation protocols to reduce soil inoculum
• Properly curing tubers immediately after harvest to heal skin wounds
• Applying recommended fungicides to seed tubers before planting