Diaporthe sojae

Systematic position and nature of the pathogen. Diaporthe sojae is an ascomycete fungus belonging to the Diaporthales order. It is a significant phytopathogen known to cause severe diseases in soybean crops, most notably Phomopsis seed decay and stem blight, which pose a major threat to global soybean production.

Diseases and host plants. The fungus primarily attacks soybean (Glycine max). Typical symptoms include seedling damping-off, stem necrosis, and decay of pods and seeds. Infected seeds often appear shriveled, discolored, or covered in a white fungal mat, leading to poor germination rates and reduced stand establishment.

Biology and life cycle. The pathogen has a complex life cycle including both sexual and asexual reproductive stages. The fungus survives the winter as mycelium within infected crop residues, seeds, and soil. When environmental conditions become favorable, it produces pycnidia, releasing conidia that spread via wind and rain splashes to infect new soybean tissues.

Conditions for spread and economic impact. High humidity and warm temperatures (ranging from +20°C to +28°C) during the reproductive stages of soybeans are highly conducive to disease development. The pathogen causes significant losses by reducing seed quality, decreasing protein and oil content, and weakening plant stems, which results in lodging and lower harvest yields.

Management and control. Integrated disease management is essential to control Diaporthe sojae. Key practices include the use of high-quality fungicide-treated seeds, long-term crop rotation to reduce inoculum buildup, and thorough incorporation of crop residues into the soil. Furthermore, applying foliar fungicides during the R3–R5 growth stages can significantly mitigate disease pressure.