Submitted to: Mycoscience
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/15/2005
Publication Date: 6/15/2005
Citation: Aoki, T., O Donnell, K., Scandiani, M.M. 2005. Sudden death syndrome of soybean in South America is caused by four species of Fusarium: Fusarium brasiliense sp. nov., F. cuneirostrum sp. nov., F. tucumaniae and F. virguliforme. Mycoscience. 46:162-183. Interpretive Summary: The economically devastating disease of soybean called sudden death syndrome (SDS) causes hundreds of millions U.S. dollar losses in North America and South America due to reduction in yields annually. The fungal pathogen reported to be the cause of SDS has been called Fusarium solani f. sp. glycines based on the perceived host specificity of this pathogen to soybean. However, results published in 2003 by us demonstrated that at least two morphologically and genetically distinct species are responsible for SDS, Fusarium tucumaniae in Argentina and F. virguliforme in the U.S. The primary objectives of this study were to determine: 1) whether more than one species of Fusarium was responsible for SDS in Brazil and Argentina based on additional pathogen surveys, 2) determine whether morphological and DNA characters could be used to reliably distinguish the species causing SDS, and 3) to determine whether strains of the species could induce SDS symptoms in greenhouse experiments. Here we report that four morphologically and genetically distinct species cause SDS in South America. In addition to these four species, a fifth species pathogenic to dry bean was able to induce typical SDS symptoms in the pathogenicity experiment.
Technical Abstract: Soybean sudden death syndrome (SDS) pathogens and dry bean root-rot pathogens were studied taxonomically, phylogenetically and pathologically. Detailed phenotypic comparisons of macro- and microscopic features and phylogenetic analyses of multilocus DNA sequence data, including those on the nuclear ribosomal intergenic spacer region and the single copy nuclear gene translation elongation factor 1-alpha, indicated that they included five distinct species of Fusarium. Two new species that were causing soybean SDS in Brazil, F. brasiliense and F. cuneirostrum, were formally described. Fusarium cuneirostrum is responsible for soybean SDS in Brazil and dry bean or mung bean root-rot in the United States, Canada and Japan. Strains of each species, including F. cuneirostrum isolates from dry bean and mung bean and F. phaseoli isolates from dry bean, were inoculated on soybean cultivar Pioneer 9492RR to determine their pathogenicity. Although intraspecific variation in pathogenicity was observed, all of the species were able to induce typical SDS symptoms on soybean plants in the artificial inoculation tests. Comparisons of the key diagnostic morphological features revealed that all five species can be diagnosed using conidial morphology.