Phomopsis seed decay

Phomopsis seed decay, caused by the fungus Diaporthe sojae (also known as Phomopsis sojae), is a prevalent and destructive disease affecting soybean crops worldwide. This pathogen compromises the structural integrity of the plant and significantly degrades the quality and viability of the harvested seeds.

The disease primarily targets soybean plants throughout their growth cycle, from seedling emergence to maturity. Beyond soybeans, the pathogen can survive on the debris of various other legume species. The infection spreads through wind-borne spores, rain splash, and the planting of contaminated seeds, which serve as a primary reservoir for the disease in new fields.

Diagnostic symptoms often appear as grayish-brown lesions near the nodes or the base of the stems. As the disease progresses, infected tissues develop numerous small, black, pepper-like structures known as pycnidia. In severe cases, the entire plant may exhibit premature senescence, leading to thin, shriveled pods that contain cracked or chalky white seeds.

The development of Diaporthe sojae is highly dependent on environmental conditions. Periods of extended wet and warm weather during the reproductive growth stages are critical for the rapid spread of the fungus. High humidity combined with temperatures between +20°C and +25°C creates an ideal environment for spore germination and infection propagation.

Management of this disease requires an integrated approach. Farmers are advised to prioritize the use of high-quality, fungicide-treated seeds and to implement crop rotation cycles that avoid soybeans for at least three years. Proper soil management, including the burial of crop residues and the selection of resistant cultivars, remains the most effective way to minimize the impact of Phomopsis on yield.

The economic impact of Phomopsis seed decay is substantial, as it leads to reduced marketability of the soybean crop and significant losses in seedling vigor for subsequent seasons. Vigilant monitoring during the mid-to-late growth stages is essential to assess the level of infection and plan timely intervention with foliar fungicides if necessary.