Phoma rot of potato

The causative agent of potato phoma rot is the fungus Juxtiphoma eupyrena (formerly known as Phoma exigua var. exigua). It is a significant phytopathogen responsible for dry rot of tubers, which primarily manifests during storage but also affects growing plants in the field, leading to severe agricultural losses.

The primary host for this fungus is the potato. The pathogen infects tubers, stems, and sometimes the root system. By colonizing these tissues, the fungus not only compromises the current harvest but also persists in the soil and on crop debris, making it a recurring threat for subsequent growing seasons.

The symptoms on tubers appear as dark, slightly sunken lesions with distinct margins. When the tuber is cut, the internal tissue shows dry, crumbly rot with hollow pockets, often containing white or grayish mycelium. On stems, the disease presents as dark brown, elongated spots that can cause the canopy to wither prematurely.

Development and spread of the fungus are favored by moist soil conditions and moderate temperatures. Infection typically occurs through mechanical wounds sustained during harvesting operations. Once the pathogen enters the tuber, it colonizes the storage parenchyma, leading to extensive tissue decay if storage ventilation and temperature control are inadequate.

Effective management of phoma rot requires an integrated approach due to the soil-borne nature of the pathogen. Key practices for prevention and control include:

• Implementing a sound crop rotation plan with at least 3–4 years between potato crops.
• Sourcing only certified, disease-free seed potatoes.
• Minimizing mechanical injury during harvest to prevent pathogen entry.
• Curing tubers adequately before storage and maintaining optimal storage climate (cool and dry).
• Applying appropriate fungicide treatments to seed potatoes to suppress initial infection.