Submitted to: Plant Cell Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/14/1998
Publication Date: N/A
Interpretive Summary: Soybean sudden death syndrome (SDS) is caused by the soilborne fungus, Fusarium solani. The symptoms of SDS include root rot, crown necrosis and vascular discoloration of roots and stems, but the most conspicuous symptoms occur on leaves as yellowing and proceed to premature defoliation. Foliar symptoms are caused by fungal toxins produced in the plant roots and translocated to leaves. The fungal toxin has not been isolated from plants, but has been found in culture filtrates of the fungus growing on liquid medium. The objective of this study was to evaluate the phytotoxicity of fungal culture filtrates using a viability stain of soybean suspension cultured cells and a soybean seedling stem-cutting assay. There was a high correlation between soybean foliar symptom severity and percentage of stained soybean suspension cultured cells and symptom severity of stem cuttings. Both methods were useful to determine the phytotoxicity of fungal culture filtrates. This research is important because it provides a reliable and efficient bioassay when evaluating potential toxins from fungal culture filtrates. These results should be helpful to other public researchers and to private industry researchers working on bioassay of fungal toxins, which can be detrimental to plants and animals.
Technical Abstract: The phytotoxicity of culture filtrates from Fusarium solani f. sp. glycines, the fungus that causes sudden death syndrome (SDS) of soybean (glycine max), was tested using a viability stain and a stem-cutting assay. Soybean suspension cultured cells from a SDS-susceptible cultivar were exposed to cell-free culture filtrates of F. solani f. sp. glycines or F. solani non-SDS isolates for 2, 4, 6 and 8 d and then stained with 0.1% phenosafranin. The percentage of dead soybean suspension cultured cells was significantly greater (P<0.001) using filtrates from SDS than non-SDS isolates, and it increased over time and with higher concentrations of culture filtrate. Cuttings of soybean seedlings with stems immersed in culture filtrates of SDS isolates had SDS-like foliar symptoms, but not when immersed in filtrates of non-SDS isolates. There was a high correlation (r=0.94, P<0.001) between soybean foliar symptom severity and percentage of stained soybean suspension cultured cells. Both methods can be used to determine the phytotoxicity of fungal culture filtrates.