Tests to Assess Weathering Effects on Soybean Seed Quality
Excessive rainfall following soybean maturation, especially for early maturing varieties, often leads to "weathering" of soybeans. Weathering has a negative effect on seed quality, most often detected during seed germination tests.
One common component of weathering in North Carolina is infection of soybeans by Phomopsis longicolla and pathovars of Diaporthe phaseolorum, the fungi causing Phomopsis seed decay. If the reduction in germination observed with weathered soybeans is caused by the Phomopsis seed decay fungi, the quality can be regained with the use of an appropriate fungicidal seed treatment.
Seed Analysts with the NCDA&CS Seed Testing Laboratory observe and note mold, decayed portions of seed and seedlings, broken radicles and other factors limiting germination potential. This additional information can help in assessing the quality of seed. Seed treatments do not correct certain deficiencies; however, they can help reduce or eliminate the negative impacts of most seedborne fungi.
Other tests conducted in the Seed Section provide additional information useful in management decisions. Accelerated Aging is a stress test used to assess seed vigor. The Sand Test can indicate the ability of the seed to overcome stress induced by seedborne fungi. The Agar Test is used to actually identify the fungi present. This test is sensitive for the detection of Phomopsis longicolla and related species of Diaporthe.
Although these tests are not run routinely on every soybean sample submitted to the Seed Testing Laboratory and Seed Pathology Laboratory, they are conducted internally to confirm problems observed. These tests are available by special arrangement with the Seed Section.