Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/12/1995
Publication Date: N/A
Interpretive Summary: Sudden death syndrome (SDS) of soybean is caused by the soilborne fungus, Fusarium solani. The fungus infects roots and produces a toxin that moves in the plant to cause very pronounced symptoms on leaves which leads to early leaf drop and causes seeds to be smaller in size. The disease occurs throughout most of the US soybean production area and appears to be increasingly important constraint to production. When the fungus is grown in pure culture, culture filtrates can be extracted. In this paper, a toxin from the fungal culture extracts was partially characterized. Samples containing a single protein caused browning on soybean calli; necrosis on detached soybean cotyledons and leaves; and caused yellowing, curling, and drying of attached soybean cotyledons and leaves. This study isolated and characterized a protein produced by the fungus that appears to be important in symptom development of SDS of soybeans. This study signifies the first step in identifying the toxin responsible for leaf symptoms and will lead to further research involving selection of plants that are resistant to the toxin as well as genetic studies dealing with the fungal genes involved in toxin production.
Technical Abstract: A phytotoxic polypeptide, identified in culture filtrates of Fusarium solani the causal agent of soybean sudden death syndrome, was heat unstable, negatively charged, absorbed by 10% charcoal and destroyed by proteinase K. The toxicity of the culture filtrates and fractions obtained during purification was bioassayed by measuring browning of soybean calli. Purification of the phytotoxin was achieved by gel filtration Sephadex G-50 chromatography followed by ion exchange chromatography on a DE-52 column. The purified protein migrated as a single band on sodium dodecyl sulfate-polyacrylamide gels with an estimated molecular weight of 17 kD. The sequence of the N-terminal 15 amino acids could be determined indicating that indeed a peptide was present. Samples containing this single protein caused browning on soybean calli; necrosis on detached soybean cotyledons and leaves; and caused yellowing, curling, and drying of attached soybean cotyledons and leaves.