Phoma stem canker

Phoma stem canker, caused by the fungus Plenodomus lingam, is a devastating disease affecting Brassica species worldwide, particularly oilseed rape. The disease is known for causing significant yield losses by impairing nutrient and water transport within the infected plants.

The host range of this pathogen includes oilseed rape (canola), cabbage, cauliflower, broccoli, and various mustard species. The fungus persists in plant debris within the soil and can be seed-borne, serving as a primary inoculum source for subsequent growing seasons.

Initial symptoms include leaf spotting characterized by light gray lesions studded with small black fruiting bodies called pycnidia. As the disease progresses, it invades the stem base, creating deep, necrotic cankers that lead to plant lodging, brittle stems, and early senescence before harvest.

Development and spread of the disease are heavily influenced by environmental factors such as high humidity, rainfall, and moderate temperatures ranging from 15°C to 25°C. Rain-splashed and wind-borne spores facilitate the rapid dispersal of the pathogen throughout a field during the growing season.

Economic impact can be severe, with potential yield reductions exceeding 50% in heavily infested fields. Effective management strategies involve a combination of practices:

• using certified, disease-free, and fungicide-treated seeds;
• implementing a strict crop rotation of at least 3-4 years between Brassica crops;
• ploughing down infected crop residues to prevent spore survival;
• timely application of systemic fungicides during the stem elongation stage.