Phomopsis seed decay of soybean

The fungus Diaporthe nomurai is a significant phytopathogen responsible for phomopsis seed decay and stem blight in soybean crops. As an ascomycete, it persists in the environment as mycelium in crop residues and infected seeds. The pathogen thrives under specific environmental conditions, making it a persistent challenge for soybean production worldwide.

The primary host for Diaporthe nomurai is soybean (Glycine max). The disease affects various plant parts, including the stem, leaves, petioles, and pods. By attacking the vascular tissues, the fungus disrupts the transport of nutrients and water, which ultimately leads to stunted plant growth and premature death of the tissues.

Field symptoms typically appear as reddish-brown or dark lesions at the stem nodes, often accompanied by pycnidia development. Leaves exhibit interveinal chlorosis and necrosis. The most critical sign of infection is observed on seeds: they often appear shriveled, elongated, and covered with a white, chalky fungal crust, leading to poor germination rates.

Environmental conditions characterized by prolonged rainfall and high humidity during the reproductive stages are optimal for the spread of Diaporthe nomurai. Conidia are disseminated through splash and wind, facilitating rapid transmission within the canopy. These environmental factors are crucial for farmers to monitor during the season to predict potential outbreaks.

The economic impact of this disease is severe, as it reduces both seed quality and total yield. Infected seeds are often lightweight and have low oil content, which significantly lowers market value. In extreme cases, the entire harvest can be downgraded due to fungal contamination, making control measures essential for profitable farming.

• Sourcing certified, disease-free seed lots.
• Implementing crop rotation with non-host plants for 3+ years.
• Timely application of systemic fungicides during pod development.
• Maintaining optimal planting density to improve air circulation.
• Incorporating resistant soybean varieties into the production plan.