Soybean sudden death syndrome causal agent Fusarium brasiliense present in Michigan

Authors: WANG, JIE - Michigan State University; SANG, HYUNKYU - Michigan State University; JACOBS, JANETTE - Michigan State University; OUDMAN, KJIRSTEN - Michigan State University; Hanson, Linda; CHILVERS, MARTIN - Michigan State University

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/8/2018
Publication Date: 4/1/2019
Citation: Wang, J., Sang, H., Jacobs, J.L., Oudman, K.A., Hanson, L.E., Chilvers, M. 2019. Soybean sudden death syndrome causal agent Fusarium brasiliense present in Michigan. Plant Disease. 103:1234-1243. https://doi.org/10.1094/PDIS-08-18-1332-RE.
DOI: https://doi.org/10.1094/PDIS-08-18-1332-RE

Interpretive Summary: One of the most important disease on soybean worldwide is sudden death syndrome (SDS). This is caused by fungal strains in what used to be called Fusarium solani. Fusarium solani is now known to be a complex of many different species. The main causal agent of SDS known to occur in North America is Fusarium virguliforme, although at least three species cause the disease in other parts of the world. In 2014 and 2016, SDS symptoms were found in two soybean fields on the same farm in Michigan. Analysis of three different genes did not identify the expected F. virguliforme. Instead, the majority of the isolates were Fusarium brasiliense, a species known to cause SDS, especially in South America, but not previously reported from soybean in the USA. In addition, five other Fusarium species were isolated from diseased plants. One of these, an as yet unnamed species, also caused SDS symptoms, and was similar to an isolate associated with SDS in South Africa. The other four species caused root rot symptoms, but not the typical SDS leaf symptoms. One of these, F. phaseoli is known as a pathogen of dry bean. Current SDS management in the USA has focused on F. virguliforme, but these findings indicate that additional species need to be considered for both SDS and root rot management in this important crop.

Technical Abstract: Sudden death syndrome (SDS), caused by members of the Fusarium solani species complex (FSSC) clade 2, is a major and economically important disease in soybean (Glycine max) worldwide. The primary causal agent of SDS isolated to date in North America has been Fusarium virguliforme. In 2014 and 2016, SDS symptoms were found in two soybean fields located on the same farm in Michigan. Forty-five and 25 Fusarium strains were isolated from roots of the SDS-symptomatic soybeans in each field. Phylogenetic analysis of the partial elongation factor (EF-1a), the nuclear ribosomal DNA intergenic spacer region (rDNA IGS), and RNA polymerase second large subunit (RPB2) sequences revealed that the primary FSSC species isolated was Fusarium brasiliense (58% and 36% in each field) and the remaining Fusarium strains were identified as F. cuneirostrum, F. phaseoli, an undescribed Fusarium sp. from FSSC clade 2, and strains in FSSC clade 5 and FSSC clade 11. Molecular identification was supported with morphological analysis and a pathogenicity assay. The soybean seedling pathogenicity assay indicated that F. brasiliense was capable of causing typical foliar SDS symptoms. Both root rot and foliar disease severity was variable by strain, just as it is in F. virguliforme. Both FSSC 5 and FSSC 11 strains were also capable of causing root rot, but SDS symptoms were not detected. Significantly, this is the first report of F. brasiliense causing SDS in soybean in the United States, and the first report of F. cuneirostrum, F. phaseoli, Fusarium sp., FSSC 5, and FSSC 11 associated with or causing root rot of soybean in Michigan.