Phoma stem canker

Phoma stem canker, caused by various species of the fungus Plenodomus (formerly Phoma lingam), is a destructive fungal disease affecting a wide range of crops, most notably oilseed rape. This pathogen is known for its ability to cause severe damage to the vascular system of the plant, resulting in significant yield losses on a global scale.

The fungus is primarily spread via pycnidiospores, which are dispersed by rain splash and wind from infected plant debris. The infection cycle begins when spores land on the leaves and penetrate the tissue, eventually migrating to the base of the stem where they cause deep, necrotic lesions that compromise the structural integrity of the plant.

Symptoms initially appear as small, light-colored leaf spots dotted with tiny black fruiting bodies known as pycnidia. As the fungus progresses, these lesions spread to the stem, resulting in "canker" symptoms where the lower stem becomes blackened, shriveled, and may eventually snap under pressure. Root rot can also occur, leading to stunted growth and premature plant death.

Environmental conditions play a crucial role in the development and spread of Plenodomus. Warm, humid weather combined with frequent rain showers provides the ideal climate for spore production and dispersal. Poor field drainage and dense canopy growth create microclimates that trap moisture, further facilitating the rapid progression of the disease across a field.

The economic impact of this disease is profound, as it directly affects the plant's ability to transport nutrients and water during the grain-filling stage. Growers must rely on an integrated disease management approach to minimize losses. This includes cultural practices to reduce inoculum and the timely application of fungicides to protect the crop during vulnerable growth stages.

• Utilizing crop rotation with non-host species for a minimum of 3-4 years.
• Ensuring the use of certified disease-free or treated seeds.
• Implementing deep tillage practices to bury crop residues.
• Selecting cultivars with genetic resistance or tolerance to the pathogen.
• Applying systemic fungicides at the early stages of disease appearance.