Phoma stem blight of lupin

Phoma stem blight is a destructive fungal disease caused by the pathogen Plenodomus lupini. This fungus predominantly attacks various lupin species, affecting their stems, leaves, and pods. It is recognized as a significant constraint to lupin production in many agricultural regions, leading to severe yield losses and degraded grain quality.

The primary clinical symptoms include the development of dark brown or greyish lesions on the stems and petioles. As the infection progresses, the lesions expand, often causing the stem to weaken or snap. On the surface of these necrotic lesions, small black pycnidia (fruiting bodies) become visible, which serve as the primary source for further spore dispersal within the field.

The development and spread of Plenodomus lupini are highly dependent on environmental factors, particularly high humidity and moderate temperatures. The fungus survives primarily on infected crop debris left in the soil or through contaminated seed lots. Extended periods of rainfall promote the release of spores from the pycnidia, facilitating rapid infection of neighboring healthy plants.

The economic impact of this disease is significant, as it severely damages the plant's vascular system. This disruption prevents the transport of nutrients to the developing pods, resulting in shriveled, low-quality seeds. In cases of severe infection, the stems collapse entirely, leading to total loss of affected plants and difficulty during the harvesting process.

Integrated pest management is essential for effective control. This includes using certified, disease-free seed and treating seeds with appropriate fungicides before planting. Crop rotation is also critical, allowing for a break period of at least four years between lupin crops. Additionally, incorporating crop residues deeply into the soil significantly reduces the overwintering population of the pathogen.