Submitted to: Mycologia
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/15/2003
Publication Date: 7/15/2003
Citation: AOKI, T., O DONNELL, K., HOMMA, Y., LATTANZI, A.R. SUDDEN DEATH SYNDROME OF SOYBEAN IS CAUSED BY TWO MORPHOLOGICALLY AND PHYLOGENETICALLY DISTINCT SPECIES WITHIN THE FUSARIUM SOLANI SPECIES COMPLEX: F. VIRGULIFORME IN NORTH AMERICA AND F. TUCUMANIAE IN SOUTH AMERICA. MYCOLOGIA. 2003. V. 95. P. 660-684. Interpretive Summary: Sudden death syndrome (SDS) of soybean has reached epidemic proportions in North and South America during the past decade. To assess whether the same pathogen is responsible for SDS in both hemispheres, molecular and morphological data were collected and analyzed to examine the evolutionary origins and genetic diversity of the SDS pathogen, Fusarium solani f. sp. glycines. The molecular and morphological data revealed that two separate species are responsible for the SDS disease of soybean: F. virguliforme, formerly known as F. solani f. sp. glycines, in North America and F. tucumaniae in South America. DNA sequence data collected in this study were used to develop a molecular diagnostic test to rapidly detect and distinguish the two SDS pathogens. Results of this study are important to plant pathologists, plant breeders and quarantine officials who need to know that soybean SDS is caused by at least two different pathogens. DNA sequence data collected in this study are being used to develop a molecular diagnostic test to rapidly detect and distinguish the two SDS pathogens.
Technical Abstract: The plant disease called sudden death syndrome has become a serious constraint to commercial production of soybean in North and South America during the past decade. To assess whether the primary etiological agent is panmictic in both hemispheres, morphological and molecular phylogenetic analyses were conducted on strains selected to represent the known pathogenic and genetic diversity of this pathogen. Maximum parsimony analysis of DNA sequences from the nuclear ribosomal intergenic region and the single copy nuclear gene translation elongation factor 1-alpha, together with detailed morphological comparisons of the conidial features, indicate that SDS of soybean in North and South America is caused by two phylogenetically and morphologically distinct species. Fusarium virguliforme sp. nov., formally known as F. solani f. sp. glycines, is described and illustrated for the SDS pathogen in North America, and F. tucumaniae sp. nov. is proposed for the South American pathogen. The molecular phylogenetic results challenge the forma specialis naming system because pathogenicity to soybean may have evolved convergently in F. tucumaniae and F. virguliforme. Phylogenetic evidence indicates the two SDS pathogens do not share a most recent common ancestor since F. tucumaniae was resolved as a sister to a pathogen of Phaseolus vulgaris, F. phaseoli comb. nov. All three pathogens appear to have evolutionary origins in the Southern hemisphere since they are deeply nested within a South American clade of the F. solani species complex.