Phomopsis Seed decay:

     Phomopsis seed rot occurs when harvest is delayed due to rainy, wet weather. Seed infection may reduce seed quality, vigor, and viability. Severely diseased seeds appear moldy and may be graded lower, which leads to dockage at the elevator. Planting diseased, poor-quality beans will result in reduced stands that may reduce yields. Pod and stem blight also occurs when soybeans mature during wet weather and harvest is delayed. These soybeans may be caused by a number of different fungi in the Diaporthe-Phomopsis complex. Phomopsis seed decay is caused primarily by Phomopsis longicolla, but other Diaporthe/Phomopsis spp. also can cause seed decay.

     Severely infected seeds are shriveled, elongated, and cracked and appear white and chalky. Seeds also may be infected and not show symptoms. Affected seeds usually do not germinate or are slow to germinate. Seed infection may cause pre- and post emergence dampening-off, and under severe conditions, stands can be reduced enough to lower yield.

   Symptoms of Phomopsis seed rot, pod and stem blight are readily apparent after the plants reach physiological maturity. Dead petioles, stems, and pods may be covered with small black specks, which are the fruiting bodies of the fungus (pycnidia). The pycnidia are usually arranged in parallel rows along the stem. During less favorable weather conditions, pycnidia may be confined to small areas of the stem near the soil surface or around the lower nodes of the stem. Pycnidia are also found scattered on discolored, poorly developed pods. Seeds that are infected have a range of symptoms from none to severe. Affected seed are usually cracked, shriveled, and covered with white mold. These severely infected seeds rarely germinate when planted. Less severely infected seed may germinate, but seedlings may show signs of seedling blight. Seedlings developing from moldy seed may have brown to reddish colored lesions on the cotyledons, or reddish-brown streaks may develop on the stem at or below the soil surface.

      Infested crop debris and soil are the major sources of primary inoculum. However, diseased seeds are an important factor in the long-range dissemination of the pathogen. Seed infection tends to be more severe when harvest is delayed, when early-maturing cultivars are grown, or when crops are grown in regions where warm; humid weather prevails at harvest time. More seed decay occurs in plants that are deficient in potassium, infected with one or more viruses, such as soybean mosaic poly virus, or heavily attacked by insects.

For more information visit: http://www.seedbuzz.com/knowledge-center/article/phomopsis-seed-decay