Phoma stem canker

The causative agent of the disease is the fungus Phoma lingam (anamorph of Leptosphaeria maculans), which causes Phoma stem canker or blackleg. This fungus is a serious threat to crop production as it colonizes the stem base, directly interfering with nutrient and water uptake throughout the plant's life cycle.

This pathogen primarily targets crops belonging to the Brassicaceae family. Oilseed rape is the most economically significant host, suffering major yield losses worldwide. However, the fungus is also highly prevalent in cabbage, broccoli, cauliflower, Brussels sprouts, and various cruciferous weeds that serve as alternative hosts for the pathogen.

Early symptoms appear as pale, round spots on leaves, often dotted with small black fruiting bodies known as pycnidia. As the infection progresses, it travels down the petiole to the main stem, creating a necrotic lesion near the crown. This results in stem girdling, which weakens the plant structure, causing premature ripening and significant lodging under windy conditions.

The development and spread of Phoma lingam are heavily influenced by environmental conditions, particularly cool, wet weather, which facilitates the release and dispersal of spores. The fungus can survive for several seasons in crop debris remaining in the soil, and seed-borne infection represents a major pathway for introducing the disease into new fields.

The impact of stem canker is severe, often resulting in significant reductions in seed yield and oil content. Effective management requires an integrated approach including the selection of resistant cultivars, use of fungicide-treated certified seeds, strict adherence to crop rotation intervals, and strategic fungicide applications during the stem elongation phases of plant growth.

• Crop rotation to break the disease cycle
• Use of disease-resistant varieties
• Fungicide application at critical growth stages
• Removal or deep burial of crop residues